3367:. As the optical experimental clocks move beyond their microwave counterparts in terms of accuracy and stability performance, this puts them in a position to replace the current standard for time, the caesium fountain clock. In the future this might lead to redefining the caesium microwave-based SI second, and other new dissemination techniques at the highest level of accuracy to transfer clock signals will be required that can be used in both shorter-range and longer-range (frequency) comparisons between better clocks and to explore their fundamental limitations without significantly compromising their performance. The BIPM reported in December 2021 based on the progress of optical standards contributing to TAI the Consultative Committee for Time and Frequency (CCTF) initiated work towards a redefinition of the second expected during the 2030s.
14036:
3849:(2021), 3 options were considered for the redefinition of the second sometime around 2026, 2030, or 2034. The first redefinition approach considered was a definition based on a single atomic reference transition. The second redefinition approach considered was a definition based on a collection of frequencies. The third redefinition approach considered was a definition based on fixing the numerical value of a fundamental constant, such as making the Rydberg constant the basis for the definition. The committee concluded there was no feasible way to redefine the second with the third option, since no physical constant is known to enough digits currently to enable realizing the second with a constant.
382:
860:, which rely on the 1.4 GHz hyperfine transition in atomic hydrogen, are also used in time metrology laboratories. Masers outperform any commercial caesium clock in terms of short-term frequency stability. In the past, these instruments have been used in all applications that require a steady reference across time periods of less than one day (frequency stability of about 1 part in ten for averaging times of a few hours). Because some active hydrogen masers have a modest but predictable frequency drift with time, they have become an important part of the BIPM's ensemble of commercial clocks that implement International Atomic Time.
551:
3169:
3957:. Galileo started offering global Early Operational Capability (EOC) on 15 December 2016, providing the third, and first non-military operated, global navigation satellite system. Galileo System Time (GST) is a continuous time scale which is generated on the ground at the Galileo Control Centre in Fucino, Italy, by the Precise Timing Facility, based on averages of different atomic clocks and maintained by the Galileo Central Segment and synchronised with TAI with a nominal offset below 50 nanoseconds. According to the European GNSS Agency, Galileo offers 30 nanoseconds timing accuracy.
658:
46:
3291:
3935:
2342:
1241:) on a hyperfine transition, the field in the cavity oscillates, and the cavity is tuned for maximum microwave amplitude. Alternatively, in a caesium or rubidium clock, the beam or gas absorbs microwaves and the cavity contains an electronic amplifier to make it oscillate. For both types, the atoms in the gas are prepared in one hyperfine state prior to filling them into the cavity. For the second type, the number of atoms that change hyperfine state is detected and the cavity is tuned for a maximum of detected state changes.
3356:
oscillators are in slightly different environments. These are causing differing reactions to gravity, magnetic fields, or other conditions. This miniaturized clock network approach is novel in that it uses an optical lattice of strontium atoms and a configuration of six clocks that can be used to demonstrate relative stability, fractional uncertainty between clocks and methods for ultra-high-precision comparisons between optical atomic clock ensembles that are located close together in a metrology facility.
4353:(this corresponds to a 1 degree uncertainty in the radiation environment as seen by the atoms in NIST-F1). To improve the performance of the NIST primary frequency standard, we sought to reduce the uncertainty due to the BBR effect. To accomplish this goal and to better understand the accepted model of the BBR shift, we developed NIST-F2, a laser-cooled Cs fountain primary frequency standard in which the microwave cavity structure and flight tube operate at cryogenic temperatures (
14030:
309:
1024:
13719:
4035:. Some manufacturers may label radio clocks as atomic clocks, because the radio signals they receive originate from atomic clocks. Normal low-cost consumer-grade receivers that rely on the amplitude-modulated time signals have a practical accuracy uncertainty of ± 0.1 second. This is sufficient for many consumer applications. Instrument grade time receivers provide higher accuracy. Radio clocks incur a propagation delay of approximately 1
1077:
4110:
726:. The closer the frequency is to the inherent oscillation frequency of the atoms, the more atoms will switch states. Such correlation allows very accurate tuning of the frequency of the microwave radiation. Once the microwave radiation is adjusted to a known frequency where the maximum number of atoms switch states, the atom and thus, its associated transition frequency, can be used as a timekeeping oscillator to measure elapsed time.
2231:
918:
1119:
2373:. The list contains the frequency values and the respective standard uncertainties for the rubidium microwave transition and for several optical transitions. These secondary frequency standards are accurate at the level of 10; however, the uncertainties provided in the list are in the range 10 – 10 since they are limited by the linking to the caesium primary standard that currently (2018) defines the second.
13729:
114:
3919:. Periodic corrections are performed to the on-board clocks in the satellites to keep them synchronized with ground clocks. The GPS navigation message includes the difference between GPST and UTC. As of July 2015, GPST is 17 seconds ahead of UTC because of the leap second added to UTC on 30 June 2015. Receivers subtract this offset from GPS Time to calculate UTC.
3027:
3034:'s strontium optical atomic clock is based on neutral atoms. Shining a blue laser onto ultracold strontium atoms in an optical trap tests how efficiently a previous burst of light from a red laser has boosted the atoms to an excited state. Only those atoms that remain in the lower energy state respond to the blue laser, causing the fluorescence seen here.
1768:("LO") are heterodyned to near zero frequency by harmonics of the repeating variation in feedback sensitivity to the LO frequency. The effect places new and stringent requirements on the LO, which must now have low phase noise in addition to high stability, thereby increasing the cost and complexity of the system. For the case of an LO with
2121:
769:. They do this by designing and building frequency standards that produce electric oscillations at a frequency whose relationship to the transition frequency of caesium 133 is known, in order to achieve a very low uncertainty. These primary frequency standards estimate and correct various frequency shifts, including relativistic
3081:. A major obstacle to developing an optical clock is the difficulty of directly measuring optical frequencies. This problem has been solved with the development of self-referenced mode-locked lasers, commonly referred to as femtosecond frequency combs. Before the demonstration of the frequency comb in 2000,
2688:
ion clock. These were the most accurate clocks that had been constructed, with neither clock gaining nor losing time at a rate that would exceed a second in over a billion years. In
February 2010, NIST physicists described a second, enhanced version of the quantum logic clock based on individual ions
1014:
atom moves at a much slower speed of 130 m/s due to its greater mass. The hyperfine frequency of caesium (~9.19 GHz) is also higher than other elements such as rubidium (~6.8 GHz) and hydrogen (~1.4 GHz). The high frequency of caesium allows for more accurate measurements. Caesium
574:
in the 1990s led to increasing accuracy of atomic clocks. Lasers enable the possibility of optical-range control over atomic states transitions, which has a much higher frequency than that of microwaves; while optical frequency comb measures highly accurately such high frequency oscillation in light.
3960:
The March 2018 Quarterly
Performance Report by the European GNSS Service Centre reported the UTC Time Dissemination Service Accuracy was ≤ 7.6 nanoseconds, computed by accumulating samples over the previous 12 months, and exceeding the ≤ 30 ns target. Each Galileo satellite has two passive
3294:
JILA's 2017 three-dimensional (3-D) quantum gas atomic clock consists of a grid of light formed by three pairs of laser beams. A stack of two tables is used to configure optical components around a vacuum chamber. Shown here is the upper table, where lenses and other optics are mounted. A blue laser
2957:
In a next phase, these labs strive to transmit comparison signals in the visible spectrum through fibre-optic cables. This will allow their experimental optical clocks to be compared with an accuracy similar to the expected accuracies of the optical clocks themselves. Some of these labs have already
1392:
than mechanical devices. Atomic clocks can also be isolated from environmental effects to a much higher degree. Atomic clocks have the benefit that atoms are universal, which means that the oscillation frequency is also universal. This is different from quartz and mechanical time measurement devices
1084:
The BIPM defines the unperturbed ground-state hyperfine transition frequency of the rubidium-87 atom, 6 834 682 610.904 312 6 Hz, in terms of the caesium standard frequency. Atomic clocks based on rubidium standards are therefore regarded as secondary representations of
960:
National metrology institutions maintain an approximation of UTC referred to as UTC(k) for laboratory k. UTC(k) is distributed by the BIPM's
Consultative Committee for Time and Frequency. The offset UTC-UTC(k) is calculated every 5 days, the results are published monthly. Atomic clocks record UTC(k)
3355:
In
February 2022, scientists at the University of Wisconsin-Madison reported a "multiplexed" optical atomic clock, where individual clocks deviated from each other with an accuracy equivalent to losing a second in 300 billion years. The reported minor deviation is explainable as the concerned clock
2653:
Twenty-first century experimental atomic clocks that provide non-caesium-based secondary representations of the second are becoming so precise that they are likely to be used as extremely sensitive detectors for other things besides measuring frequency and time. For example, the frequency of atomic
3997:(DSAC), a miniaturized, ultra-precise mercury-ion atomic clock, into outer space. NASA said that the DSAC would be much more stable than other navigational clocks. The clock was successfully launched on 25 June 2019, activated on 23 August 2019 and deactivated two years later on 18 September 2021.
3968:
The
Galileo navigation message includes the differences between GST, UTC and GPST, to promote interoperability. In the summer of 2021, the European Union settled on a passive hydrogen maser for the second generation of Galileo satellites, starting in 2023, with an expected lifetime of 12 years per
3930:
provides an alternative to the Global
Positioning System (GPS) system and is the second navigational system in operation with global coverage and of comparable precision. GLONASS Time (GLONASST) is generated by the GLONASS Central Synchroniser and is typically better than 1,000 nanoseconds. Unlike
3390:
The most accurate caesium clocks based on the caesium frequency of 9.19 GHz have an accuracy between 10–10. Unfortunately, they are big and only available in large metrology labs and not useful for factories or industrial environments that would use an atomic clock for GPS accuracy but cannot
3351:
over 6 hours. Recently it has been proved that the quantum entanglement can help to further enhance the clock stability. In 2020 optical clocks were researched for space applications like future generations of global navigation satellite systems (GNSSs) as replacements for microwave based clocks.
3299:
In 2017 JILA reported an experimental 3D quantum gas strontium optical lattice clock in which strontium-87 atoms are packed into a tiny three-dimensional (3-D) cube at 1,000 times the density of previous one-dimensional (1-D) clocks, such as the 2015 JILA clock. A comparison between two regions of
3180:
The rare-earth element ytterbium (Yb) is valued not so much for its mechanical properties but for its complement of internal energy levels. "A particular transition in Yb atoms, at a wavelength of 578 nm, currently provides one of the world's most accurate optical atomic frequency standards," said
1396:
A clock's quality can be specified by two parameters: accuracy and stability. Accuracy is a measurement of the degree to which the clock's ticking rate can be counted on to match some absolute standard such as the inherent hyperfine frequency of an isolated atom or ion. Stability describes how the
1322:
changes and are not very accurate. The most accurate clocks use atomic vibrations to keep track of time. Clock transition states in atoms are insensitive to temperature and other environmental factors and the oscillation frequency is much higher than any of the other clocks (in microwave frequency
1274:
Many of the newer clocks, including microwave clocks such as trapped ion or fountain clocks, and optical clocks such as lattice clocks use a sequential interrogation protocol rather than the frequency modulation interrogation described above. An advantage of sequential interrogation is that it can
1142:
Hydrogen masers are used for flywheel oscillators in laser-cooled atomic frequency standards and broadcasting time signals from national standards laboratories, although they need to be corrected as they drift from the correct frequency over time. The hydrogen maser is also useful for experimental
956:
TAI is not distributed in everyday timekeeping. Instead, an integer number of leap seconds are added or subtracted to correct for the Earth's rotation, producing UTC. The number of leap seconds is changed so that mean solar noon at the
Greenwich meridian does not deviate from UTC noon by more than
3259:
excites the atoms between two of their energy levels. Having established the stability of the clocks, the researchers are studying external influences and evaluating the remaining systematic uncertainties, in the hope that they can bring the clock's accuracy down to the level of its stability. An
8170:
Masuda, T.; Yoshimi, A.; Fujieda, A.; Fujimoto, H.; Haba, H.; Hara, H.; Hiraki, T.; Kaino, H.; Kasamatsu, Y.; Kitao, S.; Konashi, K.; Miyamoto, Y.; Okai, K.; Okubo, S.; Sasao, N.; Seto, M.; Schumm, T.; Shigekawa, Y.; Suzuki, K.; Stellmer, S.; Tamasaku, K.; Uetake, S.; Watanabe, M.; Watanabe, T.;
4058:
effect has been well documented. Atomic clocks are effective at testing general relativity on ever smaller scales. A project to observe twelve atomic clocks from 11 November 1999 to
October 2014 resulted in a further demonstration that Einstein's theory of general relativity is accurate at small
3339:
in about two hours. According to Jun Ye, "this represents a significant improvement over any previous demonstrations". Ye further commented "the most important potential of the 3D quantum gas clock is the ability to scale up the atom numbers, which will lead to a huge gain in stability" and "the
1130:
Hydrogen masers have superior short-term stability compared to other standards, but lower long-term accuracy. The long-term stability of hydrogen maser standards decreases because of changes in the cavity's properties over time. The relative error of hydrogen masers is 5 × 10 for periods of 1000
925:
National laboratories usually operate a range of clocks. These are operated independently of one another and their measurements are sometimes combined to generate a scale that is more stable and more accurate than that of any individual contributing clocks. This scale allows for time comparisons
6833:
Liu, Liang; Lü, Desheng; Chen, Weibiao; Li, Tang; Qu, Qiuzhi; Wang, Bin; Li, Lin; Ren, Wei; Dong, Zuoren; Zhao, Jianbo; Xia, Wenbing; Zhao, Xin; Ji, Jingwei; Ye, Meifeng; Sun, Yanguang; Yao, Yuanyuan; Song, Dan; Liang, Zhaogang; Hu, Shanjiang; Yu, Dunhe; Hou, Xia; Shi, Wei; Zang, Huaguo; Xiang,
3085:
techniques were needed to bridge the gap between radio and optical frequencies, and the systems for doing so were cumbersome and complicated. With the refinement of the frequency comb, these measurements have become much more accessible and numerous optical clock systems are now being developed
3399:
In 2022, the best realisation of the second is done with caesium primary standard clocks such as IT-CsF2, NIST-F2, NPL-CsF2, PTB-CSF2, SU–CsFO2 or SYRTE-FO2. These clocks work by laser-cooling a cloud of caesium atoms to a microkelvin in a magneto-optic trap. These cold atoms are then launched
1126:
The BIPM defines the unperturbed optical transition frequency of the hydrogen-1 neutral atom, 1 233 030 706 593 514 Hz, in terms of the caesium standard frequency. Atomic clocks based on hydrogen standards are therefore regarded as secondary representations of the
8044:
von der Wense, Lars; Seiferle, Benedict; Laatiaoui, Mustapha; Neumayr, Jürgen B.; Maier, Hans-Jörg; Wirth, Hans-Friedrich; Mokry, Christoph; Runke, Jörg; Eberhardt, Klaus; Düllmann, Christoph E.; Trautmann, Norbert G.; Thirolf, Peter G. (5 May 2016). "Direct detection of the Th nuclear clock
3906:
provides very accurate timing and frequency signals. A GPS receiver works by measuring the relative time delay of signals from a minimum of four, but usually more, GPS satellites, each of which has at least two onboard caesium and as many as two rubidium atomic clocks. The relative times are
2807:, which was better than existing 2019 optical atomic clock technology. Although a precise clock remains an unrealized theoretical possibility, efforts through the 2010s to measure the transition energy culminated in the 2024 measurement of the optical frequency with sufficient accuracy (
2222:, and, for many of the newer clocks, is significantly larger. Analysis of the effect and its consequence as applied to optical standards has been treated in a major review (Ludlow, et al., 2015) that lamented on "the pernicious influence of the Dick effect", and in several other papers.
1244:
Most of the complexity of the clock lies in this adjustment process. The adjustment tries to correct for unwanted side-effects, such as frequencies from other electron transitions, temperature changes, and the spreading in frequencies caused by the vibration of molecules including
1559:
2654:
clocks is altered slightly by gravity, magnetic fields, electrical fields, force, motion, temperature and other phenomena. The experimental clocks tend to continue to improve, and leadership in performance has shifted back and forth between various types of experimental clocks.
940:
Before TAI is published, the frequency of the result is compared with the SI second at various primary and secondary frequency standards. This requires relativistic corrections to be applied to the location of the primary standard which depend on the distance between the
1096:) and short-term stability. They are used in many commercial, portable and aerospace applications. Modern rubidium standard tubes last more than ten years, and can cost as little as US$ 50. Some commercial applications use a rubidium standard periodically corrected by a
842:
Primary frequency standards can be used to calibrate the frequency of other clocks used in national laboratories. These are usually commercial caesium clocks having very good long-term frequency stability, maintaining a frequency with a stability better than 1 part in
3612:, or even higher. They have better stabilities than microwave clocks, which means that they can facilitate evaluation of lower uncertainties. They also have better time resolution, which means the clock "ticks" faster. Optical clocks use either a single ion, or an
897:
when averaged over 15 minutes. Receivers allow the simultaneous reception of signals from several satellites, and make use of signals transmitted on two frequencies. As more satellites are launched and start operations, time measurements will become more accurate.
331:
in his 1873 Treatise on
Electricity and Magnetism: 'A more universal unit of time might be found by taking the periodic time of vibration of the particular kind of light whose wave length is the unit of length.' Maxwell argued this would be more accurate than the
3980:. BeiDou Time (BDT) is a continuous time scale starting at 1 January 2006 at 0:00:00 UTC and is synchronised with UTC within 100 ns. BeiDou became operational in China in December 2011, with 10 satellites in use, and began offering services to customers in the
1955:
3984:
region in
December 2012. On 27 December 2018 the BeiDou Navigation Satellite System started to provide global services with a reported timing accuracy of 20 ns. The final, 35th, BeiDou-3 satellite for global coverage was launched into orbit on 23 June 2020.
8409:
Elwell, R.; Schneider, Christian; Jeet, Justin; Terhune, J. E. S.; Morgan, H. W. T.; Alexandrova, A. N.; Tran Tan, Hoang Bao; Derevianko, Andrei; Hudson, Eric R. (2 July 2024). "Laser excitation of the Th nuclear isomeric transition in a solid-state host".
10973:
Grebing, Christian; Al-Masoudi, Ali; Dörscher, Sören; Häfner, Sebastian; Gerginov, Vladislav; Weyers, Stefan; Lipphardt, Burghard; Riehle, Fritz; Sterr, Uwe; Lisdat, Christian (2016). "Realization of a timescale with an accurate optical lattice clock".
2298:
technology. Such clocks are also called optical clocks where the energy level transitions used are in the optical regime (giving rise to even higher oscillation frequency), which thus, have much higher accuracy as compared to traditional atomic clocks.
10580:
Schuldt, Thilo; Gohlke, Martin; Oswald, Markus; Wüst, Jan; Blomberg, Tim; Döringshoff, Klaus; Bawamia, Ahmad; Wicht, Andreas; Lezius, Matthias; Voss, Kai; Krutzik, Markus; Herrmann, Sven; Kovalchuk, Evgeny; Peters, Achim; Braxmaier, Claus (July 2021).
3763:
2246:
developed a series of seven caesium-133 microwave clocks named NBS-1 to NBS-6 and NIST-7 after the agency changed its name from the National Bureau of Standards to the National Institute of Standards and Technology. The first clock had an accuracy of
892:
The signal received from one satellite in a metrology laboratory equipped with a receiver with an accurately known position allows the time difference between the local time scale and the GNSS system time to be determined with an uncertainty of a few
633:. The second is expected to be redefined when the field of optical clocks matures, sometime around the year 2030 or 2034. In order for this to occur, optical clocks must be consistently capable of measuring frequency with accuracy at or better than
2954:. These four European labs are developing and host a variety of experimental optical clocks that harness different elements in different experimental set-ups and want to compare their optical clocks against each other and check whether they agree.
3833:
The only viable way to fix the Rydberg constant involves trapping and cooling hydrogen. Unfortunately, this is difficult because it is very light and the atoms move very fast, causing Doppler shifts. The radiation needed to cool the hydrogen
3059:, is a pioneer in exploiting the properties of a single ion held in a trap to develop clocks of the highest stability. The development of the first optical clock was started at NIST in 2000 and finished in 2006. See for a review up to 2020.
766:
1015:
reference tubes suitable for national standards currently last about seven years and cost about US$ 35,000. Primary frequency and time standards like the United States Time Standard atomic clocks, NIST-F1 and NIST-F2, use far higher power.
2974:
In August 2016 the French LNE-SYRTE in Paris and the German PTB in Braunschweig reported the comparison and agreement of two fully independent experimental strontium lattice optical clocks in Paris and Braunschweig at an uncertainty of
2950:; and Italy's Istituto Nazionale di Ricerca Metrologica (INRiM) in Turin labs have started tests to improve the accuracy of current state-of-the-art satellite comparisons by a factor of 10, but it will still be limited to one part in
2970:
but these span much shorter distances than the European network and are between just two labs. According to Fritz Riehle, a physicist at PTB, "Europe is in a unique position as it has a high density of the best clocks in the world".
2241:
The accuracy of atomic clocks has improved continuously since the first prototype in the 1950s. The first generation of atomic clocks were based on measuring caesium, rubidium, and hydrogen atoms. In a time period from 1959 to 1998,
3042:
was proposed by Russian physicist Vladilen Letokhov in the 1960s. The theoretical move from microwaves as the atomic "escapement" for clocks to light in the optical range, harder to measure but offering better performance, earned
1759:
Modern clocks such as atomic fountains or optical lattices that use sequential interrogation are found to generate type of noise that mimics and adds to the instability inherent in atom or ion counting. This effect is called the
868:
The time readings of clocks operated in metrology labs operating with the BIPM need to be known very accurately. Some operations require synchronization of atomic clocks separated by great distances over thousands of kilometers.
12307:
11102:
Roslund, Jonathan D.; Cingöz, Arman; Lunden, William D.; Partridge, Guthrie B.; Kowligy, Abijith S.; Roller, Frank; Sheredy, Daniel B.; Skulason, Gunnar E.; Song, Joe P.; Abo-Shaeer, Jamil R.; Boyd, Martin M. (23 August 2023).
8234:
Seiferle, B.; von der Wense, L.; Bilous, P.V.; Amersdorffer, I.; Lemell, C.; Libisch, F.; Stellmer, S.; Schumm, T.; Düllmann, C.E.; Pálffy, A.; Thirolf, P.G. (12 September 2019). "Energy of the Th nuclear clock transition".
3412:
systematic uncertainty, which is equivalent to 50 picoseconds per day. A system of several fountains worldwide contributes to International Atomic Time. These caesium clocks also underpin optical frequency measurements.
641:. In addition, methods for reliably comparing different optical clocks around the world in national metrology labs must be demonstrated, and the comparison must show relative clock frequency accuracies at or better than
3212:. There are two reasons for the possibly better precision. Firstly, the frequency is measured using light, which has a much higher frequency than microwaves, and secondly, by using many atoms, any errors are averaged.
12579:
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample".
8969:
Beloy, Kyle; Bodine, Martha I.; Bothwell, Tobias; Brewer, Samuel M.; Bromley, Sarah L.; Chen, Jwo-Sy; Deschênes, Jean-Daniel; Diddams, Scott A.; Fasano, Robert J.; Fortier, Tara M.; Hassan, Youssef S. (25 March 2021).
2928:
Insensitivity to environmental effects. Due to its small size and the shielding effect of the surrounding electrons, an atomic nucleus is much less sensitive to ambient electromagnetic fields than is an electron in an
3881:
radio transmitters. They are used at some long-wave and medium-wave broadcasting stations to deliver a very precise carrier frequency. Atomic clocks are used in many scientific disciplines, such as for long-baseline
3576:
3181:
Marianna Safronova. The estimated uncertainty achieved corresponds to about one second over the lifetime of the universe so far, 15 billion years, according to scientists at the Joint Quantum Institute (JQI) and the
680:. The atomic clock was about the size of a grain of rice with a frequency of about 9 GHz. This technology became available commercially in 2011. Atomic clocks on the scale of one chip require less than 30
1055:). The output of the frequency synthesizer is amplified and applied to a chamber containing caesium gas which absorbs the microwaves. The output current of the caesium chamber increases as absorption increases.
3472:
8108:
Thielking, J.; Okhapkin, M.V.; Glowacki, P.; Meier, D.M.; von der Wense, L.; Seiferle, B.; Düllmann, C.E.; Thirolf, P.G.; Peik, E. (2018). "Laser spectroscopic characterization of the nuclear-clock isomer Th".
10502:
Pedrozo-Peñafiel, Edwin; Colombo, Simone; Shu, Chi; Adiyatullin, Albert F.; Li, Zeyang; Mendez, Enrique; Braverman, Boris; Kawasaki, Akio; Akamatsu, Daisuke; Xiao, Yanhong; Vuletić, Vladan (16 December 2020).
534:. Timekeeping researchers are currently working on developing an even more stable atomic reference for the second, with a plan to find a more precise definition of the second as atomic clocks improve based on
2958:
established fibre-optic links, and tests have begun on sections between Paris and Teddington, and Paris and Braunschweig. Fibre-optic links between experimental optical clocks also exist between the American
1449:
3914:
GPST is related to but differs from TAI (International Atomic Time) and UTC (Coordinated Universal Time). GPST remains at a constant offset from TAI (TAI – GPST = 19 seconds) and like TAI does not implement
2932:
Greater number of atoms. Because of the aforementioned insensitivity to ambient fields, it is not necessary to have the clock atoms well-separated in a dilute gas. Current measurements take advantage of the
8947:
3828:
984:
The SI second is defined as a certain number of unperturbed ground-state hyperfine transitions of the caesium-133 atom. Caesium standards are therefore regarded as primary time and frequency standards.
7693:
Brewer, S. M.; Chen, J.-S.; Hankin, A. M.; Clements, E. R.; Chou, C. W.; Wineland, D. J.; Hume, D. B.; Leibrandt, D. R. (15 July 2019). "Al Quantum-Logic Clock with a Systematic Uncertainty below 10".
661:
The heart of NIST's next-generation miniature atomic clock – ticking at high "optical" frequencies – is this vapor cell on a chip, shown next to a coffee bean for scale.
12285:
2777:" in the ultraviolet frequency range. In 2003, Ekkehard Peik and Christian Tamm noted this makes a clock possible with current optical frequency-measurement techniques. In 2012, it was shown that a
13758:
4009:
announced a drive to upgrade to the U.S. military timekeeping systems for greater precision over time when sensors do not have access to GPS satellites, with a plan to reach precision of 1 part in
3857:
A redefinition must include improved optical clock reliability. TAI must be contributed to by optical clocks before the BIPM affirms a redefinition. A consistent method of sending signals, such as
7569:
6444:
Santarelli, G.; Audoin, C.; Makdissi, A.; Laurent, P.; Dick, G.J.; Clairon, A. (1998). "Frequency stability degradation of an oscillator slaved to a periodically interrogated atomic resonator".
6536:
6446:
2220:
10333:
9713:
1283:(LO) for a time of perhaps a second or so. Analysis of the final state of the atoms is then used to generate a correction signal to keep the LO frequency locked to that of the atoms or ions.
2116:{\displaystyle \sigma _{y,\,{\rm {Dick}}}(\tau )\approx {\frac {\sigma _{y}^{\rm {LO}}}{\sqrt {2\ln(2)}}}\cdot \left|{\frac {\sin(\pi d)}{\pi d}}\right|\cdot {\sqrt {\frac {T_{c}}{\tau }}}.}
578:
The first advance beyond the precision of caesium clocks occurred at NIST in 2010 with the demonstration of a "quantum logic" optical clock that used aluminum ions to achieve a precision of
11974:
8753:
3089:
As in the radio range, absorption spectroscopy is used to stabilize an oscillator—in this case, a laser. When the optical frequency is divided down into a countable radio frequency using a
2329:
The performance of primary and secondary frequency standards contributing to International Atomic Time (TAI) is evaluated. The evaluation reports of individual (mainly primary) clocks are
1816:
12315:
9653:
10212:
7377:
7286:
7195:
5539:
Dimarcq, Noel; Gertsvolf, Marina; Mileti, Gaetano; Bize, Sebastien; Oates, Christopher; Peik, Ekkehard; Calonico, Davide; Ido, Tetsuya; Tavella, Patrizia; Meynadier, Frédéric (2024).
3907:
mathematically transformed into three absolute spatial coordinates and one absolute time coordinate. GPS Time (GPST) is a continuous time scale and theoretically accurate to about 14
362:
is reduced by temperature fluctuations. This led to the idea of measuring the frequency of an atom's vibrations to keep time much more accurately, as proposed by James Clerk Maxwell,
10700:
McGrew, W. F.; Zhang, X.; Fasano, R. J.; Schaffer, S. A.; Beloy, K.; Nicolodi, D.; Brown, R. C.; Hinkley, N.; Milani, G.; Schioppo, M.; Yoon, T. H.; Ludlow, A. D. (6 December 2018).
7916:
3973:
193:
416:
nowadays, for higher frequencies and narrower resonances in the oscillating fields. Kolsky, Phipps, Ramsey, and Silsbee used this technique for molecular beam spectroscopy in 1950.
8515:
Zhang, Chuankun; Ooi, Tian; Higgins, Jacob S.; Doyle, Jack F.; von der Wense, Lars; Beeks, Kjeld; Leitner, Adrian; Kazakov, Georgy; Li, Peng; Thirolf, Peter G.; Schumm, Thorsten;
4618:
4094:. Accurate timekeeping is needed to prevent illegal trading ahead of time, in addition to ensuring fairness to traders on the other side of the globe. The current system known as
3639:
3391:
afford to build a whole metrology laboratory for one atomic clock. Researchers have designed a strontium optical clock that can be moved around in an air-conditioned car trailer.
3165:
depends on the element that is stimulated. For example, calcium optical clocks resonate when red light is produced, and ytterbium clocks resonate in the presence of violet light.
2925:
Higher frequency. All other things being equal, a higher-frequency transition offers greater stability for simple statistical reasons (fluctuations are averaged over more cycles).
9873:
1441:
3295:
beam excites a cube-shaped cloud of strontium atoms located behind the round window in the middle of the table. Strontium atoms fluoresce strongly when excited with blue light.
2946:
In June 2015, the National Physical Laboratory (NPL) in Teddington, UK; the French department of Time-Space Reference Systems at the Paris Observatory (LNE-SYRTE); the German
933:(TAI), then adding leap seconds as necessary. TAI is a weighted average of around 450 clocks in some 80 time institutions. The relative stability of TAI is around one part in
1943:
1058:
The remainder of the circuitry simply adjusts the running frequency of the VCXO to maximize the output current of the caesium chamber which keeps the oscillator tuned to the
10120:
9953:
5260:
Nicholson, T.L.; Campbell, S.L.; Hutson, R.B.; Marti, G.E.; Bloom, B.J.; McNally, R.L.; Zhang, W.; Barrett, M.D.; Safronova, M.S.; Strouse, G.F.; Tew, W.L. (21 April 2015).
2161:
1911:
1636:
815:
microwave transition and other optical transitions, including neutral atoms and single trapped ions. These secondary frequency standards can be as accurate as one part in
691:
The National Institute of Standards and Technology created a program NIST on a chip to develop compact ways of measuring time with a device just a few millimeters across.
10446:
5876:
1703:
1679:
1585:
1384:
9978:
T.L. Nicholson; S.L. Campbell; R.B. Hutson; G.E. Marti; B.J. Bloom; R.L. McNally; W. Zhang; M.D. Barrett; M.S. Safronova; G.F. Strouse; W.L. Tew; J. Ye (21 April 2015).
2369:
A list of frequencies recommended for secondary representations of the second is maintained by the International Bureau of Weights and Measures (BIPM) since 2006 and is
11539:
11170:
7759:
251:
of the involved atomic clocks is important because the smaller the error in time measurement, the smaller the error in distance obtained by multiplying the time by the
13934:
10480:
9070:
4078:
seconds. Given its quantum nature and the fact that time is a relativistic quantity, atomic clocks can be used to see how time is influenced by general relativity and
3606:
1754:
1357:
11771:
5585:
4310:
Thomas P. Heavner; Elizabeth A. Donley; Filippo Levi; Giovanni Costanzo; Thomas E. Parker; Jon H. Shirley; Neil Ashby; Stephan Barlow; Steven R. Jefferts (May 2014).
3492:
3359:
Optical clocks are currently (2022) still primarily research projects, less mature than rubidium and caesium microwave standards, which regularly deliver time to the
5825:
12193:"Definition and Realization of the System Time of COMPASS/BeiDou Navigation Satellite System, Chunhao Han, Beijing Global Information Center,(BGIC), Beijing, China"
7983:
Campbell, C.; Radnaev, A.G.; Kuzmich, A.; Dzuba, V.A.; Flambaum, V.V.; Derevianko, A. (2012). "A single ion nuclear clock for metrology at the 19th decimal place".
1863:
1836:
1727:
1656:
13857:
11829:
11765:"GLONASS Interface Control Document, Navigation radiosignal In bands L1, L2 (ICD L1, L2 GLONASS), Russian Institute of Space Device Engineering, Edition 5.1, 2008"
8943:
2753:
which current atomic clocks measure. Most nuclear transitions operate at far too high a frequency to be measured, but the exceptionally low excitation energy of
7456:
1609:
1279:, during which the atom or ion collections are analyzed, renewed and driven into a proper quantum state, after which they are interrogated with a signal from a
6172:
Jain, Pratik; Priya, Priyanka; Ram, T. V. S.; Parikh, K. S.; Bandi, Thejesh N. (1 December 2021). "Digital lock-in amplifier for space rubidium atomic clock".
5158:
1271:. When a clock is first turned on, it takes a while for the oscillator to stabilize. In practice, the feedback and monitoring mechanism is much more complex.
1267:
properties of the atomic transition frequency of the caesium can be used to tune the microwave oscillator to the same frequency, except for a small amount of
718:
An atomic clock is based on a system of atoms which may be in one of two possible energy states. A group of atoms in one state is prepared, then subjected to
12180:
6495:
6428:
J. A. Barnes, A. R. Chi, L. S. Cutler, D. J. Healey, D. B. Leeson, T. E. McGunigal, J. A. Mullen, W. L. Smith, R. Sydnor, R. F. C. Vessot, G. M. R. Winkler:
2357:, more stable and more reliable. The Cold Atom Clock Experiment in Space (CACES) testing a Cold Atom Clock in Earth orbit in microgravity conditions and the
12277:
5235:
665:
In addition to increased accuracy, the development of chip-scale atomic clocks has expanded the number of places atomic clocks can be used. In August 2004,
11800:
9036:
3101:
is also divided by that factor. Although the bandwidth of laser phase noise is generally greater than stable microwave sources, after division it is less.
12063:
9735:
3227:
over a 7-hour period was published on 22 August 2013. At this stability, the two optical lattice clocks working independently from each other used by the
50:
NIST physicists Steve Jefferts (foreground) and Tom Heavner with the NIST-F2 caesium fountain atomic clock, a civilian time standard for the United States
13765:
12644:
11851:
7561:
3340:
ability to scale up both the atom number and coherence time will make this new-generation clock qualitatively different from the previous generation".
3010:) apart at the NIST lab, its partner lab JILA, and the University of Colorado all in Boulder, Colorado over air and fiber optic cable to a precision of
781:
shift) and several other factors. The best primary standards currently produce the SI second with an accuracy approaching an uncertainty of one part in
11448:
9817:
7134:
3208:, which is as accurate as the experiment could measure. These clocks have been shown to keep pace with all three of the caesium fountain clocks at the
5440:
Bothwell, Tobias; Kennedy, Colin J.; Aeppli, Alexander; Kedar, Dhruv; Robinson, John M.; Oelker, Eric; Staron, Alexander; Ye, Jun (16 February 2022).
3188:
In 2013 optical lattice clocks (OLCs) were shown to be as good as or better than caesium fountain clocks. Two optical lattice clocks containing about
10329:
9709:
8171:
Yasuda, Y.; Yamaguchi, A.; Yoda, Y.; Yokokita, T.; Yoshimura, M.; Yoshimura, K. (12 September 2019). "X-ray pumping of the Th nuclear clock isomer".
1729:
over which the measurements are averaged increases from seconds to hours to days. The stability is most heavily affected by the oscillator frequency
6009:
3118:
These techniques allow the atoms or ions to be highly isolated from external perturbations, thus producing an extremely stable frequency reference.
145:. Electron states in an atom are associated with different energy levels, and in transitions between such states they interact with a very specific
11919:
11597:
10307:
6035:
4369:
1189:
11967:
11375:"Consultative Committee for Units (CCU) Report of the 25th meeting (21-23 September 2021) to the International Committee for Weights and Measures"
1199:
This definition makes the caesium oscillator the primary standard for time and frequency measurements, called the caesium standard. Following the
7535:
228:
to within one second while being based on clocks that are based on the definition of the second, though leap seconds will be phased out in 2035.
1764:
and is typically the primary stability limitation for the newer atomic clocks. It is an aliasing effect; high frequency noise components in the
499:
vibrations of the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom. Prior to that it was defined by there being
129:(formerly HP) 5071A caesium beam clocks. The black units in the foreground are Microsemi (formerly Sigma-Tau) MHM-2010 hydrogen maser standards.
11884:"1 The Definition and Implementation of Galileo System Time (GST). ICG-4 WG-D on GNSS time scales. Jérôme Delporte. CNES – French Space Agency"
11682:
6918:
5624:
4664:
3505:
3287:". At this frequency uncertainty, this JILA optical lattice clock is expected to neither gain nor lose a second in more than 15 billion years.
3228:
2243:
742:
666:
420:
285:
11999:
11627:
9895:
Bloom, B. J.; Nicholson, T. L.; Williams, J. R.; Campbell, S. L.; Bishof, M.; Zhang, X.; Zhang, W.; Bromley, S. L.; Ye, J. (22 January 2014).
9374:
6811:
3400:
vertically by laser light. The atoms then undergo Ramsey excitation in a microwave cavity. The fraction of excited atoms are then detected by
965:, time signal transmitters, and speaking clocks. In addition, GNSS provides time information accurate to a few tens of nanoseconds or better.
873:(GNSS) provide a satisfactory solution to the problem of time transfer. Atomic clocks are used to broadcast time signals in the United States
9649:
6122:
2307:
762:
432:
371:
316:
10271:
10211:
S. L. Campbell; R. B. Hutson; G. E. Marti; A. Goban; N. Darkwah Oppong; R. L. McNally; L. Sonderhouse; W. Zhang; B. J. Bloom; J. Ye (2017).
9598:
7850:
Gao, Qi; Zhou, Min; Han, Chengyin; Li, Shangyan; Zhang, Shuang; Yao, Yuan; Li, Bo; Qiao, Hao; Ai, Di; Lou, Ge; Zhang, Mengya (22 May 2018).
7373:
7282:
7191:
6984:
6780:
5986:
961:
to no more than 100 nanoseconds. In some countries, UTC(k) is the legal time that is distributed by radio, television, telephone, Internet,
13850:
12669:
9627:
7955:
7166:
6099:
5821:
3360:
804:
3419:
1554:{\displaystyle \sigma _{y,\,{\rm {atoms}}}(\tau )\approx {\frac {\Delta \nu }{\nu _{0}{\sqrt {N}}}}{\sqrt {\frac {T_{\text{c}}}{\tau }}},}
11708:
10364:
10089:
5004:
3308:
in 1 hour of averaging time. This precision value does not represent the absolute accuracy or precision of the clock, which remain above
11945:
11742:
10631:
Brewer, S. M.; Chen, J.-S.; Hankin, A. M.; Clements, E. R.; Chou, C. W.; Wineland, D. J.; Hume, D. B.; Leibrandt, D. R. (15 July 2019).
7013:
5371:
Brewer, S. M.; Chen, J.-S.; Hankin, A. M.; Clements, E. R.; Chou, C. W.; Wineland, D. J.; Hume, D. B.; Leibrandt, D. R. (15 July 2019).
4289:
610:
in 2015. Scientists at NIST developed a quantum logic clock that measured a single aluminum ion in 2019 with a frequency uncertainty of
12033:
9433:
4668:
2353:
Most research focuses on the often conflicting goals of making the clocks smaller, cheaper, more portable, more energy efficient, more
12641:
12092:
9869:
9092:
9033:
7593:
5705:
5677:
5343:
4070:
between two layers of atoms separated by one millimeter using a strontium optical clock cooled to 100 nanokelvins with a precision of
11656:
582:. Optical clocks are a very active area of research in the field of metrology as scientists work to develop clocks based on elements
12419:
6744:
1104:). This achieves excellent short-term accuracy, with long-term accuracy equal to (and traceable to) the US national time standards.
14388:
12723:
9770:
5513:
11445:
10112:
10054:
9896:
5620:
5346:
3768:
13843:
13328:
13164:
5928:
4149:
1188:
of radiation corresponding to the transition between two energy levels of the ground state of the caesium-133 atom. In 1997, the
1044:
12348:
12199:
4747:
1756:. This is why optical clocks such as strontium clocks (429 terahertz) are much more stable than caesium clocks (9.19 GHz).
11374:
10558:
10387:
5849:
5592:
4824:
3946:
2712:, which is the first demonstration of such a clock with uncertainty below 10 and remains the most accurate clock in the world.
13788:
11890:
2282:. The goal is to redefine the second when clocks become so accurate that they will not lose or gain more than a second in the
12793:
12759:
11528:
11485:
9847:
9342:
9062:
7755:
7668:
5862:
5042:
4934:
4240:
4090:
Atomic clocks keep accurate records of transactions between buyers and sellers to the millisecond or better, particularly in
2947:
1036:
738:
424:
12695:
10472:
5733:
5059:
1291:
All timekeeping devices use oscillatory phenomena to accurately measure time, whether it is the rotation of the Earth for a
14357:
12546:
12520:
12371:
12254:
12228:
11764:
11568:
11196:
Koller, S. B.; Grotti, J.; Vogt, St.; Al-Masoudi, A.; Dörscher, S.; Häfner, S.; Sterr, U.; Lisdat, Ch. (13 February 2017).
8829:"Hyper-precise atomic clocks face off to redefine time – Next-generation timekeepers can only be tested against each other"
8780:"Hyper-precise atomic clocks face off to redefine time – Next-generation timekeepers can only be tested against each other"
5812:
3869:
The development of atomic clocks has led to many scientific and technological advances such as precise global and regional
3331:(a quantum gas for Fermi particles). The experimental data shows the 3D quantum gas clock achieved a residual precision of
9227:
3352:
Ye's strontium-87 clock has not surpassed the aluminum-27 or ytterbium-171 optical clocks in terms of frequency accuracy.
926:
between different clocks in the laboratory. These atomic time scales are generally referred to as TA(k) for laboratory k.
165:
The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency,
4263:
3977:
3379:
621:
At JILA in September 2021, scientists demonstrated an optical strontium clock with a differential frequency precision of
405:
and microwave absorption signals. Unfortunately, this caused a side effect with a light shift of the resonant frequency.
12148:
12000:"Galileo Open Service and Search and Rescue – Quarterly Performance Reports, containing measured performance statistics"
11825:
3911:. However, most receivers lose accuracy in the interpretation of the signals and are only accurate to 100 nanoseconds.
2166:
1275:
accommodate much higher Q's, with ringing times of seconds rather than milliseconds. These clocks also typically have a
1039:(VCXO) that is tunable over a narrow range. The output frequency of the VCXO (typically 5 MHz) is multiplied by a
15080:
14626:
13751:
5736:
3374:
molecules were demonstrated at-sea on a naval vessel and operated continuously in the Pacific Ocean for 20 days in the
12502:
10582:
5646:
4627:
3324:
respectively. The 3D quantum gas strontium optical lattice clock's centerpiece is an unusual state of matter called a
15090:
14108:
6116:
5183:
4456:
2370:
1136:
363:
10826:
8669:
Seiferle, Benedict; von der Wense, Lars; Thirolf, Peter G. (2017). "Lifetime measurement of the Th nuclear isomer".
125:, which provides the time standard for the U.S. Department of Defense. The rack mounted units in the background are
3927:
3846:
1775:
428:
7041:; Donaldson, R W; Hope, E G; Bangham, M J (July 1973). "Hydrogen Maser Work at the National Physical Laboratory".
3002:
In 2021, NIST compared transmission of signals from a series of experimental atomic clocks located about 1.5
13278:
12933:
12117:
7815:
6607:
4904:"Paper 1.15: "Experiments with Separated Oscillatory Fields and Hydrogen Masers," (Nobel Lecture), N. F. Ramsey,
4195:
118:
11796:
9120:
8331:
4921:, World Scientific Series in 20th Century Physics, vol. 21, WORLD SCIENTIFIC, pp. 115–127, June 1998,
953:. The TAI time-scale is deferred by a few weeks as the average of atomic clocks around the world is calculated.
929:
Coordinated Universal Time (UTC) is the result of comparing clocks in national laboratories around the world to
401:
for electron energy level transitions in atoms using light. This technique is useful for creating much stronger
15008:
14835:
14181:
13157:
12055:
11852:"European GNSS (Galileo) Open Service Signal-In-Space Operational Status Definition, Issue 1.0, September 2015"
11388:
Ren, Wei; Li, Tang; Qu, Qiuzhi; Wang, Bin; Li, Lin; Lü, Desheng; Chen, Weibiao; Liu, Liang (18 December 2020).
9526:
Golovizin, A.; Tregubov, D.; Mishin, D.; Provorchenko, D.; Kolachevsky, N.; Kolachevsky, N. (25 October 2021).
6855:
Ren, Wei; Li, Tang; Qu, Qiuzhi; Wang, Bin; Li, Lin; Lü, Desheng; Chen, Weibiao; Liu, Liang (18 December 2020).
3943:
2358:
882:
758:
240:
10905:
5902:
808:
14362:
11858:
9505:
Schmittberger, Bonnie L. (21 April 2020). "A Review of Contemporary Atomic Frequency Standards". p. 13.
8649:
3765:. The Rydberg constant describes the energy levels in a hydrogen atom with the nonrelativistic approximation
3758:{\displaystyle R_{\infty }={\frac {m_{e}e^{4}}{8\varepsilon _{0}^{2}h^{3}c}}={\frac {m_{e}c\alpha ^{2}}{2h}}}
3094:
3073:
has led to a new generation of atomic clocks. These clocks are based on atomic transitions that emit visible
1249:. One way of doing this is to sweep the microwave oscillator's frequency across a narrow range to generate a
168:
154:
28:
12748:
Geng, Yilong; Liu, Shiyu; Yin, Zi; Naik, Ashish; Prabhakar, Balaji; Rosenblum, Mendel; Vahdat, Amin (2018).
11501:
11027:
Ludlow, Andrew D; Boyd, Martin M; Ye, Jun; Peik, Ekkehard; Schmidt, Piet O (2015). "Optical atomic clocks".
9793:
7085:
5708:
1397:
clock performs when averaged over time to reduce the impact of noise and other short-term fluctuations (see
827:. This is because the uncertainty in the central caesium standard against which the secondary standards are
381:
13240:
10142:
N. Huntemann; C. Sanner; B. Lipphardt; Chr. Tamm; E. Peik (8 February 2016). "Single-Ion Atomic Clock with
8487:. This feature is assigned to the excitation of the Th nuclear isomeric state, whose energy is found to be
2693:
and aluminium. Considered the world's most precise clock in 2010 with a fractional frequency inaccuracy of
2322:
cooling of the microwave interaction region; the largest source of uncertainty in NIST-F1 is the effect of
949:
of Earth. The values of the rotating geoid and the TAI change slightly each month and are available in the
355:
8330:
Tiedau, J.; Okhapkin, M. V.; Zhang, K.; Thielking, J.; Zitzer, G.; Peik, E.; et al. (29 April 2024).
3938:
Space Passive Hydrogen Maser used in ESA Galileo satellites as a master clock for an onboard timing system
2983:
via a newly established phase-coherent frequency link connecting Paris and Braunschweig, using 1,415
315:(right) and Jack Parry (left) standing next to the world's first caesium-133 atomic clock in 1955, at the
14317:
14297:
14243:
14128:
13964:
13531:
11473:
10297:
9472:
9066:
6634:
5030:
3581:
Optical clocks are based on forbidden optical transitions in ions or atoms. They have frequencies around
3276:
1088:
Rubidium standard clocks are prized for their low cost, small size (commercial standards are as small as
11915:
11593:
8744:
6489:
Quessada, A.; Kovacich, R. P.; Courtillot, I.; Clairon, A.; Santarelli, G.; Lemonde, P. (2 April 2003).
4013:. The Robust Optical Clock Network will balance usability and accuracy as it is developed over 4 years.
1410:
722:
radiation. If the radiation is of the correct frequency, a number of atoms will transition to the other
141:
that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different
14789:
14766:
13984:
13969:
13907:
13886:
12883:
12863:
12396:
10632:
7483:
5372:
3279:
for an elevation change of 2 cm (0.79 in) on planet Earth that according to JILA/NIST Fellow
2914:. It is the large ratio between transition frequency and isomer lifetime which gives the clock a high
2750:
1101:
217:
10757:
Zheng, Xin; Dolde, Jonathan; Lochab, Varun; Merriman, Brett N.; Li, Haoran; Kolkowitz, Shimon (2022).
550:
14671:
14138:
13949:
13594:
13443:
13323:
12873:
12786:
8519:(4 September 2024). "Frequency ratio of the Th nuclear isomeric transition and the Sr atomic clock".
6288:
5953:
3903:
3899:
3364:
3162:
1916:
1097:
930:
874:
673:
that was 100 times smaller than an ordinary atomic clock and had a much smaller power consumption of
436:
370:
in 1949. This led to the first practical accurate atomic clock with caesium atoms being built at the
366:, and Isidor Rabi. He proposed the concept in 1945, which led to a demonstration of a clock based on
328:
269:
second) translates into an almost 30-centimetre (11.8 in) distance and hence positional error).
213:
150:
83:
12444:
6907:
6803:
2704:
In July 2019, NIST scientists demonstrated such an Al quantum logic clock with total uncertainty of
13293:
12003:
11686:
11619:
7852:"Systematic evaluation of a Yb optical clock by synchronous comparison between two lattice systems"
7086:"Proton Zemach radius from measurements of the hyperfine splitting of hydrogen and muonic hydrogen"
6286:
Ludlow, A.D.; Boyd, M.M.; Ye, J.; Peik, E.; Schmidt, P.O. (26 June 2015). "Optical atomic clocks".
5791:
4772:; Parry, J. V. L. (1955). "An Atomic Standard of Frequency and Time Interval: A Cæsium Resonator".
4696:; Parry, J. V. L. (1955). "An Atomic Standard of Frequency and Time Interval: A Cæsium Resonator".
3877:, which depend critically on frequency and time standards. Atomic clocks are installed at sites of
2129:
1868:
921:
Data points representing atomic clocks around the world that define International Atomic Time (TAI)
11325:
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
11271:
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
6772:
6103:
5978:
5761:
5680:
1614:
14398:
14176:
14078:
13994:
13989:
13549:
13200:
12470:
10395:
9591:
9382:
8671:
8412:
8339:
6972:
5662:
Lutwak, Robert (26–29 November 2007). "The Chip-Scale Atomic Clock — Prototype Evaluation".
4309:
3994:
3839:
1684:
1661:
1567:
1366:
1200:
1152:
670:
531:
293:
9623:
9146:
9095:
7159:
4384:
4345:
and is dominated by the uncertainty in the blackbody radiation (BBR) shift correction, which is
2991:) of telecom fibre-optic cable. The fractional uncertainty of the whole link was assessed to be
1192:(CIPM) added that the preceding definition refers to a caesium atom at rest at a temperature of
15070:
14666:
14619:
12903:
10081:
9736:"Ytterbium in quantum gases and atomic clocks: van der Waals interactions and blackbody shifts"
4091:
4067:
4055:
4031:
is a clock that automatically synchronizes itself by means of radio time signals received by a
3182:
3168:
3052:
1769:
1398:
767:
All-Russian Scientific Research Institute for Physical-Engineering and Radiotechnical Metrology
467:
456:
452:
406:
248:
12698:
11941:
11712:
10386:
G. Edward Marti; Ross B. Hutson; Akihisa Goban; Sara L. Campbell; Nicola Poli; Jun Ye (2018).
10356:
6684:
6410:
5540:
5209:
5085:
5008:
3588:
1732:
1335:
1326:
One of the most important factors in a clock's performance is the atomic line quality factor,
15013:
14551:
13732:
13364:
13309:
13263:
13248:
12893:
12749:
11734:
7816:"Recent Advances Concerning the Sr Optical Lattice Clock at the National Time Service Center"
7562:"Press release: NIST 'Quantum Logic Clock' Rivals Mercury Ion as World's Most Accurate Clock"
7006:
5236:"NIST's Second 'Quantum Logic Clock' Based on Aluminum Ion is Now World's Most Precise Clock"
4363:
4144:
4139:
4095:
3954:
3477:
2720:
2616:
2579:
2502:
1706:
1040:
847:
over a few months. The uncertainty of the primary standard frequencies is around one part in
413:
195:, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be
12025:
11269:
National Physical Laboratory (2011). "When should we change the definition of the second?".
9527:
9444:
9415:
7590:
6747:
14921:
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14812:
14802:
14731:
14378:
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11126:
11046:
10993:
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10723:
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10526:
10414:
10239:
10169:
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9921:
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8899:
8840:
8791:
8690:
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8256:
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8128:
8066:
8002:
7931:
7863:
7712:
7636:
7591:
NIST's Second 'Quantum Logic Clock' Based on Aluminum Ion is Now World's Most Precise Clock
7508:
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657:
232:
216:(TAI), which is maintained by an ensemble of atomic clocks around the world. The system of
87:
11649:
11197:
10385:
7610:
C.W Chou; D. Hume; J.C.J. Koelemeij; D.J. Wineland & T. Rosenband (17 February 2010).
3343:
In 2018, JILA reported the 3D quantum gas clock reached a residual frequency precision of
3048:
3026:
8:
14588:
14383:
14238:
14103:
14055:
13489:
12948:
12908:
11968:"Galileo Initial Services – Open Service – Quarterly Performance Report Oct–Nov–Dec 2017"
9762:
6010:"Clock Experiment Shows a Fundamental Connection Between Energy Consumption and Accuracy"
3232:
3082:
2937:
and place the thorium ions in a solid, which allows billions of atoms to be interrogated.
2867:
2677:
2402:
2283:
1268:
1002:
Caesium has several properties that make it a good choice for an atomic clock. Whereas a
942:
789:
333:
324:
225:
13924:
12754:. 15th USENIX Symposium on Networked Systems Design and Implementation. pp. 81–94.
12603:
11336:
11323:
Gill, Patrick (28 October 2011). "When should we change the definition of the second?".
11282:
11147:
11130:
11104:
11050:
10997:
10943:
10871:
10784:
10727:
10601:
10530:
10418:
10243:
10173:
10013:
9925:
9543:
9395:
9283:
9189:
8987:
8903:
8844:
8795:
8694:
8352:
8260:
8196:
8132:
8070:
8006:
7935:
7867:
7716:
7640:
7335:
7244:
7114:
7054:
6660:"The atomic clock with the world's best long-term accuracy is revealed after evaluation"
6508:
6364:
6311:
6253:
6185:
5467:
5295:
5171:
5111:
4973:
4785:
4709:
4568:
4521:
3267:
evaluated the absolute frequency uncertainty of a strontium-87 optical lattice clock at
2934:
811:. This list contains the frequency values and respective standard uncertainties for the
15085:
14699:
14563:
14337:
14261:
14191:
13438:
13416:
13283:
13107:
13078:
13013:
13006:
12623:
12589:
11422:
11356:
11302:
11251:
11217:
11116:
11062:
11036:
11009:
10983:
10955:
10883:
10857:
10804:
10770:
10713:
10682:
10648:
10613:
10550:
10516:
10438:
10404:
10263:
10229:
10193:
10159:
10030:
9999:
9979:
9945:
9911:
9809:
9573:
9506:
9348:
9303:
9269:
9015:
8920:
8889:
8877:
8714:
8680:
8530:
8421:
8304:
8280:
8246:
8216:
8182:
8152:
8118:
8090:
8056:
8026:
7992:
7947:
7892:
7851:
7736:
7702:
7660:
7626:
7438:
7412:
7355:
7321:
7264:
7230:
7126:
7100:
7066:
6883:
6856:
6835:
6571:
6545:
6471:
6376:
6350:
6323:
6297:
6265:
6239:
6205:
6036:"New experiment: Clocks consuming more energy are more accurate… 'cause thermodynamics"
5628:
5552:
5495:
5453:
5422:
5388:
5320:
5281:
5261:
5131:
5097:
4880:
4797:
4721:
4478:
4448:
4412:
4115:
4051:
3416:
The advantage of optical clocks can be explained by the statement that the instability
2741:
One theoretical possibility for improving the performance of atomic clocks is to use a
1594:
1246:
1148:
1144:
962:
906:
902:
793:
402:
348:
231:
The accurate timekeeping capabilities of atomic clocks are also used for navigation by
69:
45:
10848:
N. Poli; C. W. Oates; P. Gill; G. M. Tino (13 January 2014). "Optical atomic clocks".
10058:
9173:
4436:
3290:
2715:
The accuracy of experimental quantum clocks has since been superseded by experimental
15033:
14612:
14411:
14276:
14093:
13798:
13793:
13519:
13398:
13298:
13151:
13054:
12958:
12755:
12627:
12615:
12554:
12338:
12192:
12156:
11481:
11427:
11409:
11348:
11294:
11243:
11235:
11152:
11066:
11013:
10959:
10887:
10808:
10796:
10758:
10739:
10686:
10674:
10666:
10617:
10554:
10542:
10430:
10267:
10255:
10220:
10185:
10035:
9937:
9813:
9684:
9577:
9565:
9557:
9480:
9407:
9352:
9338:
9307:
9295:
9209:
9201:
9037:"NIST Team Compares 3 Top Atomic Clocks With Record Accuracy Over Both Fiber and Air"
9019:
9007:
8999:
8971:
8925:
8858:
8809:
8706:
8364:
8284:
8272:
8220:
8208:
8144:
8094:
8082:
8018:
7951:
7897:
7879:
7740:
7728:
7652:
7430:
7347:
7268:
7256:
7070:
6888:
6719:
6563:
6490:
6463:
6380:
6327:
6269:
6209:
6197:
6112:
5868:
5858:
5499:
5487:
5479:
5426:
5414:
5406:
5325:
5307:
5135:
5123:
5038:
4985:
4930:
4885:
4867:
4739:
4582:
4533:
4452:
4416:
4404:
4400:
4332:
4079:
4040:
3962:
3934:
3325:
3209:
3134:
3056:
2967:
2889:
2685:
2264:
1300:
1264:
1071:
792:
in the device cannot be ignored. The standard is then considered in the framework of
774:
734:
697:
are currently (2022) designing atomic clocks that implement new developments such as
587:
448:
344:
337:
12751:
Exploiting a Natural Network Effect for Scalable, Fine-grained Clock Synchronization
11255:
10701:
10504:
10388:"Imaging Optical Frequencies with 100 μHz Precision and 1.1 μm Resolution"
10197:
9257:
8718:
8030:
7664:
7442:
7359:
7062:
6575:
6531:
6516:
6488:
6475:
4816:
4437:"James Clerk Maxwell, A treatise on electricity and magnetism, first edition (1873)"
3104:
The primary systems under consideration for use in optical frequency standards are:
2420:
514:
1900. The 1968 definition was updated in 2019 to reflect the new definitions of the
14556:
14302:
14281:
14233:
14196:
14009:
13637:
13625:
13453:
13421:
13253:
13122:
13038:
13028:
12943:
12607:
11883:
11417:
11401:
11360:
11340:
11306:
11286:
11231:
11227:
11142:
11134:
11054:
11001:
10947:
10875:
10788:
10731:
10662:
10658:
10605:
10534:
10442:
10426:
10422:
10247:
10181:
10177:
10025:
10017:
9949:
9929:
9839:
9801:
9547:
9399:
9330:
9287:
9193:
8991:
8915:
8907:
8848:
8799:
8702:
8698:
8540:
8521:
8435:
8431:
8360:
8356:
8309:
8264:
8237:
8200:
8173:
8156:
8136:
8074:
8047:
8014:
8010:
7939:
7887:
7871:
7830:
7794:
7724:
7720:
7648:
7644:
7422:
7343:
7339:
7252:
7248:
7130:
7118:
7058:
6952:
6878:
6868:
6834:
Jingfeng; Peng, Xiangkai; Wang, Yuzhu (2017). "Tests of Cold Atom Clock in Orbit".
6711:
6555:
6512:
6455:
6368:
6315:
6257:
6189:
5562:
5471:
5402:
5398:
5315:
5299:
5175:
5115:
4977:
4922:
4875:
4859:
4801:
4789:
4725:
4713:
4572:
4525:
4444:
4396:
4328:
4236:
4124:
3633:
3382:
have led to the world's first commercial rackmount optical clock in November 2023.
3090:
1765:
1224:
979:
539:
122:
11080:
9403:
9334:
8972:"Frequency ratio measurements at 18-digit accuracy using an optical clock network"
7611:
6659:
6593:
5664:
36th Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting
4311:
15075:
15049:
15018:
14916:
14779:
14287:
14266:
14098:
14070:
13835:
13699:
13564:
13541:
13509:
13461:
13448:
13411:
13393:
13023:
13018:
12506:
12250:
12224:
10113:"The most accurate clock ever built only loses one second every 15 billion years"
9528:"Compact magneto-optical trap of thulium atoms for a transportable optical clock"
7597:
7309:
7218:
5650:
3613:
3375:
3070:
2390:
2319:
2311:
2295:
2256:
1946:
1405:
1220:
1208:
1132:
685:
475:
460:
440:
398:
11557:
10879:
9977:
9258:"20 years of developments in optical frequency comb technology and applications"
8944:"Optical fibre link opens a new era of time-frequency metrology, 19 August 2016"
7943:
6372:
6261:
6060:
5514:"An atomic clock measured how general relativity warps time across a millimeter"
5441:
4903:
2341:
14878:
14719:
14704:
14676:
14651:
14643:
14583:
14342:
14332:
14271:
14228:
14060:
14050:
14019:
13919:
13891:
13774:
13642:
13632:
13431:
13303:
13273:
13258:
13043:
13001:
12996:
12868:
12611:
11138:
10927:
10792:
10609:
9322:
8995:
8544:
7875:
7426:
7122:
6685:"2016 Gets Longer with Extra Second Added to New Year Countdown | Sci-News.com"
6443:
6430:
5857:. Vol. 15. International Bureau of Weights and Measures. 2020. p. 9.
5566:
5475:
5119:
4926:
4164:
4159:
4032:
3887:
3883:
3066:
2915:
2746:
1443:. The limiting instability due to atom or ion counting statistics is given by
1228:
1113:
788:
It is important to note that at this level of accuracy, the differences in the
770:
702:
571:
390:
252:
236:
24:
12645:"JILA Atomic Clocks Measure Einstein's General Relativity at Millimeter Scale"
12278:"China's BeiDou navigation satellite, rival to US GPS, starts global services"
11058:
10735:
10538:
9805:
9763:"JILA Strontium Atomic Clock Sets New Records in Both Precision and Stability"
9291:
8268:
8204:
8140:
7084:
Dupays, Arnaud; Beswick, Alberto; Lepetit, Bruno; Rizzo, Carlo (August 2003).
6319:
5442:"Resolving the gravitational redshift across a millimetre-scale atomic sample"
5179:
1658:
is the averaging period. This means instability is smaller when the linewidth
1027:
Simplified block diagram of typical commercial cesium beam frequency reference
950:
15064:
15028:
14873:
14868:
14807:
14741:
14470:
14421:
14406:
14352:
14123:
13959:
13954:
13870:
13722:
13672:
13620:
13554:
13526:
13514:
13504:
13494:
13376:
13220:
13146:
13095:
13048:
12963:
12923:
12918:
12913:
12846:
12558:
12160:
11413:
11239:
10670:
10210:
9688:
9561:
9484:
9299:
9205:
9003:
8645:
7883:
7484:"What the world's most accurate clock can tell us about Earth and the cosmos"
7400:
6723:
5872:
5483:
5410:
5311:
5127:
4989:
4871:
4586:
4537:
4408:
4207:
One second in 13.8 billion years, the age of the universe, is an accuracy of
4174:
4169:
3858:
3216:
2778:
2736:
2724:
2669:
2663:
1193:
511:
385:
A caesium atomic clock from 1975 (upper unit) and battery backup (lower unit)
281:
13743:
11005:
10251:
9197:
7609:
7399:
Leute, J.; Huntemann, N.; Lipphardt, B.; Tamm, Christian (3 February 2016).
6957:
6944:
6559:
6098:
5586:"SA.45s CSAC Chip Scale Atomic Clock (archived version of the original pdf)"
5151:"Optical frequency combs: From frequency metrology to optical phase control"
4505:
14863:
14774:
14709:
14568:
14455:
14450:
14445:
14432:
13814:
13694:
13688:
13354:
13288:
13210:
13141:
12991:
12938:
12878:
12619:
11431:
11352:
11344:
11298:
11290:
11247:
11156:
10800:
10743:
10678:
10546:
10434:
10259:
10189:
10039:
9941:
9676:
9569:
9411:
9213:
9063:"Coping With Unusual Atomic Collisions Makes an Atomic Clock More Accurate"
9011:
8929:
8862:
8813:
8710:
8368:
8276:
8212:
8148:
8086:
8022:
7901:
7732:
7656:
7434:
7351:
7260:
6892:
6567:
6467:
6224:
6201:
6147:
5491:
5418:
5329:
4889:
4577:
4552:
4529:
4198:
have demonstrated a clock that will not lose a second in 300 billion years.
4154:
4054:
predicts that clocks tick slower deeper in a gravitational field, and this
3981:
3916:
3197:
3044:
2755:
1588:
1315:
1257:
1035:
beam frequency reference, timing signals are derived from a high stability
723:
394:
359:
308:
277:
221:
142:
12499:
11405:
10330:"JILA's 3-D Quantum Gas Atomic Clock Offers New Dimensions in Measurement"
10141:
10082:"Getting Better All the Time: JILA Strontium Atomic Clock Sets New Record"
9174:"Optical frequency combs: Coherently uniting the electromagnetic spectrum"
8313:
8299:
7799:
7782:
7401:"Frequency Comparison of Yb Ion Optical Clocks at PTB and NPL via GPS PPP"
6873:
5642:
5150:
5086:"On a definition of the SI second with a set of optical clock transitions"
4956:
Hellwig, Helmut; Evenson, Kenneth M.; Wineland, David J. (December 1978).
4847:
4610:
4551:
Rabi, I. I.; Zacharias, J. R.; Millman, S.; Kusch, P. (15 February 1938).
3838:— is also difficult. Another hurdle involves improving the uncertainty in
3200:
were able to stay in synchrony with each other at a precision of at least
901:
These methods of time comparison must make corrections for the effects of
15023:
14939:
14931:
14853:
14797:
14756:
14578:
14573:
14218:
14201:
14133:
14113:
13999:
13881:
13824:
13704:
13682:
13589:
13574:
13369:
13349:
13339:
13268:
13225:
13205:
13134:
12953:
12855:
12670:"An Ultra-Precise Clock Shows How to Link the Quantum World With Gravity"
10822:
10759:"Differential clock comparisons with a multiplexed optical lattice clock"
8654:
7105:
7038:
6412:
Local oscillator induced instabilities in trapped ion frequency standards
4863:
4769:
4693:
4134:
4129:
4036:
4028:
4022:
3878:
3571:{\displaystyle \sigma (\tau )={\frac {1}{2\pi f{\sqrt {NT_{int}\tau }}}}}
3098:
3063:
2270:
The next step in atomic clock advances involves going from accuracies of
1761:
1319:
1204:
828:
797:
527:
375:
312:
97:
20:
12308:"China puts final satellite for Beidou network into orbit – state media"
9933:
9710:"Blackbody Radiation Shift: Quantum Thermodynamics Will Redefine Clocks"
8911:
8078:
7308:
Huntemann, N.; Sanner, C.; Lipphardt, B.; Tamm, Chr. (8 February 2016).
6712:"How the U.S. Built the World's Most Ridiculously Accurate Atomic Clock"
6529:
3969:
satellite. The masers are about 2 feet long with a weight of 40 pounds.
2330:
2286:. To do so, scientists must demonstrate the accuracy of clocks that use
14982:
14944:
14858:
14830:
14593:
14546:
14530:
14416:
14322:
14143:
14004:
13974:
13912:
13599:
13499:
13406:
13381:
13184:
12968:
12125:
10021:
8233:
7835:
7405:
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
6537:
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
6447:
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
6399:, pages 221–230. Proceedings of the IEEE, Vol. 54, No 2, February 1966.
6394:
6148:"NIST Primary Frequency Standards and the Realization of the SI Second"
5303:
4957:
4611:"NIST Primary Frequency Standards and the Realization of the SI Second"
4319:
3908:
3078:
2921:
A nuclear energy transition offers the following potential advantages:
1250:
894:
778:
471:
256:
23:. For the clock as a measure for risk of catastrophic destruction, see
11389:
11171:"Vector Atomic brings world's first rackmount optical clock to market"
10951:
10702:"Atomic clock performance enabling geodesy below the centimetre level"
9897:"An optical lattice clock with accuracy and stability at the 10 level"
9552:
6945:"With better atomic clocks, scientists prepare to redefine the second"
6459:
6222:
6193:
4981:
4608:
3260:
improved optical lattice clock was described in a 2014 Nature paper.
1260:
to apply feedback to control long-term drift in the radio frequency.
1023:
14959:
14490:
14327:
14211:
14186:
14166:
14083:
14035:
14029:
14014:
13662:
13579:
13215:
13127:
13102:
13083:
12973:
10501:
9323:"Towards a High-Performance Optical Clock Based on Single 171-Yb Ion"
8043:
4793:
4717:
3328:
3154:
3146:
3138:
3130:
3003:
2984:
2845:) that an experimental optical nuclear clock can now be constructed.
2774:
2690:
2681:
2346:
2291:
2287:
1360:
1232:
1076:
1059:
741:(PTB) in Germany, the National Institute of Standards and Technology
730:
719:
694:
676:
603:
595:
591:
583:
555:
146:
126:
12420:"Working Overtime: NASA's Deep Space Atomic Clock Completes Mission"
10583:"Optical clock technologies for global navigation satellite systems"
8853:
8828:
8804:
8779:
6285:
3467:{\displaystyle \sigma \propto {\frac {\Delta f}{f}}{\frac {1}{S/N}}}
409:
and others managed to reduce the light shifts to acceptable levels.
14964:
14954:
14883:
14736:
14525:
14505:
14347:
14253:
14153:
13944:
13939:
13230:
13073:
12983:
12841:
12831:
12594:
11222:
11121:
10988:
10901:
10847:
10775:
10718:
10653:
10521:
10409:
10302:
10234:
10164:
9677:"How Super-Precise Atomic Clocks Will Change the World in a Decade"
9525:
9511:
9274:
8894:
8685:
8535:
8426:
8251:
8187:
8123:
8061:
7707:
7417:
7326:
7235:
6840:
5557:
5458:
5393:
5102:
4109:
3874:
2354:
1296:
1007:
1003:
854:
812:
750:
746:
698:
523:
419:
After 1956, atomic clocks were studied by many groups, such as the
11041:
10862:
10004:
9916:
7997:
7631:
7536:"The most precise atomic clock ever made is a cube of quantum gas"
7217:
Brewer, S.; Chen, J.-S.; Hankin, A.; Clements, E. (15 July 2019).
6550:
6418:. Precise Time and Time Interval (PTTI) Conference. Redondo Beach.
6355:
6302:
6244:
5286:
4043:. Many governments operate transmitters for timekeeping purposes.
1080:
A team of United States Air Force airmen carrying a rubidium clock
917:
14974:
14893:
14845:
14635:
14520:
14510:
14440:
14312:
14223:
14088:
13569:
13559:
13481:
13472:
13457:
13344:
13189:
13112:
12821:
11505:
5005:"Atomichron: The Atomic Clock from Concept to Commercial Product"
3923:
3284:
3158:
3150:
2315:
2230:
1308:
1292:
1118:
1032:
1011:
996:
992:
988:
878:
367:
289:
273:
73:
13359:
8875:
7917:"Nuclear laser spectroscopy of the 3.5 eV transition in Th"
6915:
ERASMUS Centre – Directorate of Human Spaceflight and Operations
6223:
N. Poli; C. W. Oates; ), P. Gill; G. M. Tino (13 January 2014).
3114:
atoms packed in a three-dimensional quantum gas optical lattice.
14911:
14751:
14661:
14515:
14465:
14460:
13667:
12826:
10972:
10633:"Al+27 Quantum-Logic Clock with a Systematic Uncertainty below
9172:
Diddams, Scott A.; Vahala, Kerry; Udem, Thomas (17 July 2020).
8516:
7219:"Al Quantum-Logic Clock with a Systematic Uncertainty below 10"
6085:
5373:"Al+27 Quantum-Logic Clock with a Systematic Uncertainty below
5060:"New Atomic Clocks May Someday Redefine the Length of a Second"
3931:
GPS, the GLONASS time scale implements leap seconds, like UTC.
3371:
3280:
3142:
3119:
1312:
1253:
1169:
886:
567:
559:
519:
515:
158:
12724:"TimeChainZ – Regulatory Reporting For High-Frequency Trading"
12471:"DARPA to launch programme for creating optical atomic clocks"
10052:
9894:
8107:
6594:"Ultraprecise atomic clock poised for new physics discoveries"
5979:"NIST Launches a New U.S. Time Standard: NIST-F2 Atomic Clock"
4290:"NIST Launches a New U.S. Time Standard: NIST-F2 Atomic Clock"
2318:. The increase in precision from NIST-F1 to NIST-F2 is due to
15003:
14998:
14949:
14686:
14656:
14495:
14307:
14206:
14161:
13677:
13426:
13117:
13065:
12547:"These Physicists Watched a Clock Tick for 14 Years Straight"
12181:
China Satellite Navigation Office, Version 2.0, December 2013
11558:"The Role of GPS in Precise Time and Frequency Dissemination"
8650:"A nuclear clock prototype hints at ultraprecise timekeeping"
7612:"Frequency Comparison of Two High-Accuracy Al Optical Clocks"
6635:"Accuracy of the NPL caesium fountain clock further improved"
5801:. Consultative Committee for Time and Frequency. 20 May 2019.
5792:"Mise en pratique for the definition of the second in the SI"
4654:"Time and frequency measurement at NIST: The first 100 years"
4006:
3401:
3074:
3039:
2799:
ion could provide a total fractional frequency inaccuracy of
1611:
is the number of atoms or ions used in a single measurement,
1304:
1237:
1174:
Since 1968, the SI has defined the second as the duration of
946:
857:
138:
59:
11268:
11101:
10298:"A Fermi-degenerate three-dimensional optical lattice clock"
10213:"A Fermi-degenerate three-dimensional optical lattice clock"
8668:
8329:
8169:
7307:
6773:"NIST launches a new US time standard: NIST-F2 atomic clock"
6083:
5259:
5148:
4039:
for every 300 kilometres (186 mi) of distance from the
3823:{\displaystyle E_{n}\approx -{\frac {R_{\infty }ch}{n^{2}}}}
2999:, making comparisons of even more accurate clocks possible.
2701:, it offers more than twice the precision of the original.
2333:
by the International Bureau of Weights and Measures (BIPM).
1043:
to obtain microwaves at the frequency of the caesium atomic
545:
423:(formerly the National Bureau of Standards) in the USA, the
14906:
14901:
14746:
14723:
14604:
14500:
14485:
14475:
13929:
13866:
12816:
12802:
12343:
12118:"ESA Adds System Time Offset to Galileo Navigation Message"
7982:
7398:
6980:
6591:
6530:
Westergaard, P.G.; Lodewyck, J.; Lemonde, P. (March 2010).
4337:
Currently, the type B fractional uncertainty in NIST-F1 is
4063:
3264:
3173:
3031:
3007:
2988:
2963:
2959:
2235:
1163:
754:
681:
599:
13935:
International Earth Rotation and Reference Systems Service
12578:
12445:"DARPA Aims for More Accurate Atomic Clock to Replace GPS"
11195:
8408:
7310:"Single-Ion Atomic Clock with 3×10 Systematic Uncertainty"
6061:"A Cesium Beam Frequency Reference for Severe Environment"
5538:
5439:
3993:
In April 2015, NASA announced that it planned to deploy a
3502:
is the signal-to-noise ratio. This leads to the equation
3283:
is "getting really close to being useful for relativistic
2364:
1332:, which is defined as the ratio of the absolute frequency
113:
14480:
12149:"Trying to Get Somewhere? An Atomic Clock May Be Helping"
10699:
8968:
8752:. EMMI Workshop: The Th Nuclear Isomer Clock. Darmstadt.
7509:"New type of atomic clock keeps time even more precisely"
7083:
7037:
4550:
2948:
German National Metrology Institute (PTB) in Braunschweig
2673:
819:; however, the uncertainties in the list are one part in
244:
12640:
12372:"NASA Technology Missions Launch on SpaceX Falcon Heavy"
12225:"China GPS rival Beidou starts offering navigation data"
10756:
10630:
9091:
9032:
8300:"Shedding Light on the Thorium-229 Nuclear Clock Isomer"
7692:
7216:
6532:"Minimizing the Dick effect in an optical lattice clock"
5704:
5676:
5370:
5342:
2263:, and laser cooling of atoms, which was demonstrated by
478:
released the 5060 rack-mounted model of caesium clocks.
12771:
12509:, National Institute of Standards and Technology, 2010.
12251:"China's Beidou GPS-substitute opens to public in Asia"
11820:
11818:
10579:
9840:"NIST Ytterbium Atomic Clocks Set Record for Stability"
9473:"The most accurate clock ever made runs on quantum gas"
6743:
5347:"NIST's Quantum Logic Clock Returns to Top Performance"
4852:
Journal of Research of the National Bureau of Standards
3231:
research team would differ less than a second over the
3176:'s 2013 pair of ytterbium optical lattice atomic clocks
3038:
The idea of trapping atoms in an optical lattice using
2383:
1404:
The instability of an atomic clock is specified by its
1006:
atom moves at 1,600 m/s at room temperature and a
470:
sold more than 50 units of the first atomic clock, the
296:
of 1 second in 300 million years (relative uncertainty
11444:
10473:"JILA Team Invents New Way to 'See' the Quantum World"
9441:
Physikalisch-Technische Bundesanstalt, Division Optics
9228:"Femtosecond-Laser Frequency Combs for Optical Clocks"
8746:
Concepts and Prospects for a Thorium-229 Nuclear Clock
8440:
a narrow, laser-linewidth-limited spectral feature at
7783:"Viewpoint: Ion Clock Busts into New Precision Regime"
5159:
IEEE Journal of Selected Topics in Quantum Electronics
4955:
4066:
measured the difference in the passage of time due to
3893:
3219:
atoms, a new record for stability with a precision of
2892:
is greater than the nuclear excitation energy, giving
486:
In 1968, the duration of the second was defined to be
11908:
9327:
2021 IEEE 6th Optoelectronics Global Conference (OGC)
8878:"A clock network for geodesy and fundamental science"
6608:"What Are Optical Clocks and Why Are They Important?"
6523:
6496:
Journal of Optics B: Quantum and Semiclassical Optics
3771:
3642:
3591:
3508:
3480:
3422:
3247:
better than previous experiments. The clocks rely on
2169:
2132:
1958:
1919:
1871:
1844:
1824:
1778:
1735:
1715:
1687:
1664:
1644:
1617:
1597:
1570:
1452:
1413:
1369:
1338:
286:
National Institute of Standards and Technology (NIST)
171:
11815:
11711:. GPS Operations Center. 30 May 2012. Archived from
10505:"Entanglement on an optical atomic-clock transition"
8514:
4817:"President Piñera Receives ESO's First Atomic Clock"
4105:
3861:, must be developed before the second is redefined.
3300:
the same 3D lattice yielded a residual precision of
807:(BIPM) provides a list of frequencies that serve as
208:
when expressed in the unit Hz, which is equal to s.
12694:
11556:Dana, Peter H.; Bruce M. Penro (July–August 1990).
9702:
8876:Paul-Eric Pottie, Gesine Grosche (19 August 2016).
6491:"The Dick effect for an optical frequency standard"
6281:
6279:
5732:
5580:
5578:
5576:
4661:
2001 IEEE International Frequency Control Symposium
4609:M.A. Lombardi; T.P. Heavner; S.R. Jefferts (2007).
4553:"A New Method of Measuring Nuclear Magnetic Moment"
3636:would involve fixing the value to a certain value:
3126:are used to cool the atoms for improved precision.
2306:accuracy was first reached at the United Kingdom's
1256:at the detector. The detector's signal can then be
16:
Clock that monitors the resonant frequency of atoms
13865:
11555:
11472:
9769:. National Institute of Standards and Technology.
9256:Fortier, Tara; Baumann, Esther (6 December 2019).
8389:, and the fluorescence lifetime in the crystal is
6482:
6171:
5029:
4441:Landmark Writings in Western Mathematics 1640–1940
3822:
3757:
3600:
3570:
3486:
3466:
3378:2022. These technologies originally funded by the
2730:
2215:{\displaystyle \sigma _{y,\,{\rm {atoms}}}(\tau )}
2214:
2155:
2115:
1937:
1905:
1857:
1830:
1810:
1748:
1721:
1697:
1673:
1650:
1630:
1603:
1579:
1553:
1435:
1378:
1351:
863:
532:2019 revision of the International System of Units
284:. The primary standard for the United States, the
187:
12243:
11960:
11709:"Notice Advisory to Navstar Users (NANU) 2012034"
9171:
6422:
4506:"Space Quantization in a Gyrating Magnetic Field"
4016:
3608:of typically 1 Hz, so the Q-factor is about
15062:
11934:
11026:
10930:(12 January 2014). "Timekeepers of the future".
10053:JILA Scientific Communications (21 April 2015).
9870:"New atomic clock sets the record for stability"
7978:
7976:
7513:MIT News | Massachusetts Institute of Technology
6276:
5573:
5541:"Roadmap towards the redefinition of the second"
1709:) is larger. The stability improves as the time
1190:International Committee for Weights and Measures
11973:. European GNSS Service Centre. 28 March 2018.
9467:
9465:
9321:Zuo, Yani; Dai, Shaoyao; Chen, Shiying (2021).
9054:
8373:The nuclear resonance for the Th ions in Th:CaF
8227:
6437:
5737:"Ion Optical Clocks and Precision Measurements"
3976:satellite navigation system is operated by the
3111:neutral atoms trapped in an optical lattice and
1203:, the definition of every base unit except the
733:laboratories maintain atomic clocks: including
327:proposed measuring time with the vibrations of
300:). NIST-F2 was brought online on 3 April 2014.
212:This definition is the basis for the system of
12747:
12330:
11526:
9375:"Single-atom optical clock with high accuracy"
9255:
8325:
8323:
8101:
4264:"The world is doing away with the leap second"
3255:and trapped in an optical lattice. A laser at
2941:
2870:, this pathway is energetically prohibited in
2668:In March 2008, physicists at NIST described a
2234:The historical accuracy of atomic clocks from
1318:. However all of these are easily affected by
421:National Institute of Standards and Technology
153:. This phenomenon serves as the basis for the
14620:
13851:
13773:
13759:
12787:
11826:"Galileo's contribution to the MEOSAR system"
10110:
9980:"Systematic evaluation of an atomic clock at
9504:
8662:
7973:
5615:
5613:
5262:"Systematic evaluation of an atomic clock at
4651:
3385:
3370:In July 2022, atomic optical clocks based on
2126:This expression shows the same dependence on
1811:{\displaystyle \sigma _{y}^{\rm {LO}}(\tau )}
1131:seconds. This makes hydrogen masers good for
412:Ramsey developed a method, commonly known as
11789:
10823:"BIPM Time Coordinated Universal Time (UTC)"
9462:
9434:"On Secondary Representations of the Second"
8291:
7849:
7501:
6100:International Bureau of Weights and Measures
5822:International Bureau of Weights and Measures
4368:: CS1 maint: DOI inactive as of June 2024 (
3494:is the instability, f is the frequency, and
3361:International Bureau of Weights and Measures
1037:voltage-controlled quartz crystal oscillator
912:
879:Global Navigation Satellite System (GLONASS)
805:International Bureau of Weights and Measures
12500:"How Accurate is a Radio Controlled Clock?"
11387:
8320:
8163:
7756:"Optical Clock Precision Breaks New Ground"
7374:"Ytterbium 171 ion (688 THz) BIPM document"
7283:"Ytterbium 171 ion (642 THz) BIPM document"
6854:
6832:
4604:
4602:
4600:
4598:
4596:
3988:
3129:Atomic systems under consideration include
1303:, the vibrations of springs and gears in a
1158:
652:
481:
220:that is the basis of civil time implements
14627:
14613:
13858:
13844:
13766:
13752:
12794:
12780:
11944:. European GNSS Agency. 15 December 2016.
11478:TIME—From Earth Rotation to Atomic Physics
11198:"Transportable Optical Lattice Clock with
9862:
9785:
9372:
9320:
9060:
8508:
8393:, corresponding to an isomer half-life of
8037:
6408:
6007:
5954:"Temperature and Kinetic Energy – Answers"
5610:
5035:TIME—From Earth Rotation to Atomic Physics
4958:"Time, frequency and physical measurement"
4768:
4692:
4305:
4303:
3055:in 2005. One of 2012's Physics Nobelists,
1214:
44:
19:For a clock updated by radio signals, see
12593:
12217:
11683:"NOTICE ADVISORY TO NAVSTAR USERS (NANU)"
11650:"NAVSTAR GPS User Equipment Introduction"
11421:
11221:
11146:
11120:
11040:
10987:
10861:
10774:
10717:
10652:
10520:
10408:
10233:
10163:
10079:
10029:
10003:
9915:
9832:
9551:
9510:
9273:
8919:
8893:
8852:
8803:
8684:
8534:
8425:
8250:
8186:
8122:
8060:
7996:
7908:
7891:
7834:
7798:
7706:
7630:
7416:
7325:
7234:
7104:
6956:
6942:
6882:
6872:
6839:
6801:
6549:
6402:
6387:
6354:
6341:Poli, N (2014). "Optical atomic clocks".
6301:
6243:
5842:
5814:Explanatory Supplement of BIPM Circular T
5655:
5556:
5457:
5392:
5319:
5285:
5149:J. Ye; H. Schnatz; L.W. Hollberg (2003).
5101:
5037:. Weinheim: Wiley-VCH. pp. 191–195.
4879:
4576:
4282:
3845:In the Report of the 25th meeting of the
2181:
1970:
1464:
1363:to the linewidth of the resonance itself
708:
546:Metrology advancements and optical clocks
343:During the 1930s, the American physicist
14389:International Commission on Stratigraphy
12518:
12494:
12492:
12397:"NASA Activates Deep Space Atomic Clock"
11494:
11449:"Help with WWVB Radio Controlled Clocks"
11390:"Development of a space cold atom clock"
10926:
10354:
9794:"Precise atomic clock may redefine time"
9650:"PTB Optical nuclear spectroscopy of Th"
9431:
9368:
9366:
9364:
9362:
8332:"Laser Excitation of the Th-229 Nucleus"
7915:Peik, E.; Tamm, Chr. (15 January 2003).
7914:
7533:
6857:"Development of a space cold atom clock"
6396:Statistics of Atomic Frequency Standards
6033:
5681:"Success Story: Chip-Scale Atomic Clock"
5142:
5083:
4593:
4296:. 3 April 2014 – via www.nist.gov.
4261:
3933:
3394:
3289:
3167:
3025:
2340:
2251:, and the last clock had an accuracy of
2229:
1638:is the time required for one cycle, and
1393:that do not have a universal frequency.
1211:relies on the definition of the second.
1164:International System of Units definition
1117:
1075:
1022:
916:
656:
549:
380:
307:
224:to allow clock time to track changes in
117:The master atomic clock ensemble at the
112:
12417:
12369:
12146:
11318:
11316:
10332:(Press release). NIST. 5 October 2017.
9624:"PTB Time and Frequency Department 4.4"
8743:Peik, Ekkehard (25–27 September 2012).
8644:
8297:
7559:
6908:"Atomic clock ensemble in space (ACES)"
6587:
6585:
6431:Characterization of Frequency Stability
5900:
5786:
5784:
5782:
5233:
4300:
4150:Primary Atomic Reference Clock in Space
2365:Secondary representations of the second
1062:frequency of the hyperfine transition.
809:secondary representations of the second
259:or 1 billionth of a second (10 or
188:{\displaystyle \Delta \nu _{\text{Cs}}}
15063:
13789:Synchronous Motor and the Master Clock
12399:. NASA Jet Propulsion Laboratory (JPL)
12336:
11803:from the original on 13 September 2019
11594:"GPS time accurate to 100 nanoseconds"
9959:from the original on 17 September 2016
9251:
9249:
8826:
8777:
7019:from the original on 23 September 2015
6632:
6105:The International System of Units (SI)
5929:"NIST-F1 Cesium Fountain Atomic Clock"
5926:
5661:
5084:Lodewyck, Jérôme (16 September 2019).
5002:
4845:
4434:
4382:
4312:"First Accuracy Evaluation of NIST-F2"
2910:ions a long half-life on the order of
629:between atomic ensembles separated by
602:demonstrated a strontium clock with a
272:The main variety of atomic clock uses
14608:
13839:
13747:
12775:
12489:
12351:from the original on 10 December 2015
12288:from the original on 27 December 2018
12275:
12257:from the original on 27 December 2012
12056:"Rb Atomic Frequency Standard (RAFS)"
11574:from the original on 15 December 2012
11545:from the original on 25 October 2012.
10367:from the original on 14 December 2017
10295:
9716:from the original on 18 December 2012
9359:
8950:from the original on 14 November 2016
8549:The transition frequency between the
7753:
6987:from the original on 19 November 2011
6924:from the original on 25 December 2015
6084:National Physical Laboratory (2019).
6008:University, Lancaster (11 May 2021).
5851:BIPM Annual Report on Time Activities
5799:Bureau International Poids et Mesures
4674:from the original on 29 December 2019
4633:from the original on 12 February 2021
4479:"Milestones:First Atomic Clock, 1948"
4046:
2745:energy transition (between different
2255:. The clocks were the first to use a
1386:. Atomic resonance has a much higher
871:Global Navigational Satellite Systems
765:(NPL) in the United Kingdom, and the
739:Physikalisch-Technische Bundesanstalt
425:Physikalisch-Technische Bundesanstalt
13728:
12276:Varma, K. J. M. (27 December 2018).
12231:from the original on 3 February 2012
12205:from the original on 29 October 2020
12098:from the original on 28 October 2020
12066:from the original on 6 November 2018
11948:from the original on 15 January 2021
11896:from the original on 6 November 2016
11662:from the original on 21 October 2013
11480:. Weinheim: Wiley-VCH. p. 266.
11322:
11313:
10829:from the original on 4 November 2013
10561:from the original on 4 February 2021
10123:from the original on 27 January 2018
9876:from the original on 2 February 2014
9791:
9773:from the original on 8 December 2014
9656:from the original on 7 November 2017
9630:from the original on 7 November 2017
8759:from the original on 10 October 2021
8742:
7813:
7780:
7140:from the original on 14 January 2019
6689:Breaking Science News | Sci-News.com
6582:
6340:
6145:
5779:
5207:
4919:Spectroscopy With Coherent Radiation
4750:from the original on 17 October 2017
4503:
4430:
4428:
4426:
4262:Brumfiel, Geoff (27 November 2022).
4243:from the original on 7 December 2010
4181:
4085:
3275:, which corresponds to a measurable
3108:single ions isolated in an ion trap;
2684:. This clock was compared to NIST's
12634:
12337:Landau, Elizabeth (27 April 2015).
11980:from the original on 26 August 2019
11922:from the original on 29 August 2019
10470:
10355:Phillips, Julie (10 October 2017).
10336:from the original on 5 October 2017
10310:from the original on 6 October 2017
10092:from the original on 9 October 2015
9850:from the original on 23 August 2013
9820:from the original on 25 August 2013
9760:
9246:
9121:"The Prize's Legacy: Dave Wineland"
7762:from the original on 26 August 2019
6814:from the original on 9 October 2015
5989:from the original on 19 August 2016
5882:from the original on 14 August 2021
5831:from the original on 9 October 2022
5621:"Chip-Scale Atomic Devices at NIST"
4098:is only accurate to a millisecond.
3978:China National Space Administration
3965:atomic clocks for onboard timing.
3894:Global navigation satellite systems
3627:
2716:
566:Technological developments such as
535:
13:
12147:Belcher, David (1 November 2021).
11797:"Galileo begins serving the globe"
11777:from the original on 14 April 2016
11630:from the original on 21 March 2017
10357:"The Clock that Changed the World"
9674:
7814:Wang, Yebing (27 September 2018).
7807:
7774:
7747:
7686:
7534:Woodward, Aylin (5 October 2017).
7380:from the original on 2 August 2022
7289:from the original on 2 August 2022
7198:from the original on 2 August 2022
6703:
6139:
5077:
3947:Global Navigation Satellite System
3924:GLObal NAvigation Satellite System
3796:
3648:
3592:
3432:
2196:
2193:
2190:
2187:
2184:
2017:
2014:
1982:
1979:
1976:
1973:
1793:
1790:
1665:
1571:
1501:
1479:
1476:
1473:
1470:
1467:
1436:{\displaystyle \sigma _{y}(\tau )}
1370:
1286:
995:clock, developed in 1999, and the
463:and Frequency & Time Systems.
378:in collaboration with Jack Parry.
172:
14:
15102:
14109:Discrete time and continuous time
12418:Hartono, Naomi (1 October 2021).
12036:from the original on 6 March 2019
10908:from the original on 26 June 2015
10296:Beall, Abigail (5 October 2017).
9604:from the original on 27 June 2015
9147:"Optical Lattices: Webs of Light"
9096:"Optical Lattices: Webs of Light"
8827:Gibney, Elizabeth (2 June 2015).
8778:Gibney, Elizabeth (2 June 2015).
8475:) that decays with a lifetime of
8397:for a nucleus isolated in vacuum.
7674:from the original on 21 July 2011
7481:
7172:from the original on 4 March 2016
6943:Cartlidge, Edwin (1 March 2018).
6783:from the original on 6 April 2014
6592:University of Wisconsin-Madison.
5189:from the original on 6 March 2016
4908:(1989, The Nobel Foundation) and
4827:from the original on 1 April 2014
4423:
4000:
3021:
2657:
2302:The goal of an atomic clock with
1137:very long baseline interferometry
713:
374:in the United Kingdom in 1955 by
14034:
14028:
13727:
13718:
13717:
12741:
12716:
12688:
12662:
12572:
12544:
12538:
12512:
12463:
12437:
12411:
12389:
12363:
12300:
12269:
12185:
12174:
12140:
12110:
12078:
12048:
12030:Safran - Navigation & Timing
12018:
11992:
11876:
11844:
11832:from the original on 9 July 2016
11757:
11745:from the original on 2 June 2018
11727:
11701:
11675:
11642:
11612:
11600:from the original on 14 May 2012
11586:
11549:
11520:
11466:
11438:
11381:
11367:
11262:
11189:
11163:
11095:
11073:
11020:
10966:
10920:
10894:
10841:
10815:
10750:
10693:
10624:
10573:
10495:
10483:from the original on 17 May 2019
10464:
10452:from the original on 2 June 2020
10379:
10348:
10322:
10289:
10204:
10135:
10104:
10073:
10046:
9971:
9888:
9754:
9728:
9668:
9642:
9616:
9584:
9519:
9498:
9425:
9373:W.H. Oskay; et al. (2006).
9314:
9220:
9165:
9139:
9113:
9085:
9073:from the original on 5 June 2011
9026:
8962:
8936:
8869:
8820:
8771:
8736:
8638:
8563:excited state is determined as:
8402:
8298:Thirolf, Peter (29 April 2024).
7572:from the original on 2 June 2017
6709:
6174:Review of Scientific Instruments
6128:from the original on 4 June 2021
4449:10.1016/b978-044450871-3/50125-x
4385:"History of early atomic clocks"
4108:
4062:In 2021 a team of scientists at
3928:Russian Aerospace Defence Forces
3847:Consultative Committee for Units
2361:are examples of clock research.
1018:
347:built equipment for atomic beam
288:'s caesium fountain clock named
218:Coordinated Universal Time (UTC)
12370:Northon, Karen (25 June 2019).
10111:James Vincent (22 April 2015).
7843:
7603:
7584:
7553:
7527:
7475:
7449:
7392:
7366:
7301:
7275:
7210:
7184:
7152:
7077:
7031:
6999:
6965:
6936:
6905:
6899:
6848:
6826:
6795:
6765:
6737:
6677:
6652:
6633:Laboratory, National Physical.
6626:
6600:
6434:, NBS Technical Note 394, 1970.
6334:
6216:
6165:
6092:
6088:. National Physical laboratory.
6077:
6053:
6034:Vleugels, Anouk (23 May 2021).
6027:
6001:
5971:
5946:
5920:
5903:"NIST-F1 Cesium Fountain Clock"
5894:
5805:
5754:
5726:
5698:
5670:
5532:
5506:
5433:
5364:
5336:
5253:
5227:
5201:
5057:
5051:
5023:
4996:
4949:
4896:
4846:Ramsey, N.F. (September 1983).
4839:
4809:
4762:
4732:
4686:
4645:
4201:
4196:University of Wisconsin-Madison
4188:
3864:
3852:
3365:International Atomic Time (TAI)
2888:ions, as the second and higher
2866:atoms decay in microseconds by
2731:Nuclear (optical) clock concept
1938:{\displaystyle 0.4<d<0.7}
1591:linewidth of the clock system,
875:Global Positioning System (GPS)
864:Synchronization with satellites
445:Bureau International de l'Heure
14182:History of timekeeping devices
12519:lombardi (24 September 2009).
12314:. 23 June 2020. Archived from
12026:"Passive Hydrogen Maser (PHM)"
11232:10.1103/PhysRevLett.118.073601
10663:10.1103/physrevlett.123.033201
10427:10.1103/PhysRevLett.120.103201
10182:10.1103/PhysRevLett.116.063001
9761:Ost, Laura (22 January 2014).
8703:10.1103/PhysRevLett.118.042501
8436:10.1103/PhysRevLett.133.013201
8377:is measured at the wavelength
8361:10.1103/PhysRevLett.132.182501
8015:10.1103/PhysRevLett.108.120802
7725:10.1103/PhysRevLett.123.033201
7649:10.1103/PhysRevLett.104.070802
7560:Swenson, Gayle (7 June 2010).
7344:10.1103/PhysRevLett.116.063001
7253:10.1103/PhysRevLett.123.033201
5403:10.1103/physrevlett.123.033201
4740:"60 years of the Atomic Clock"
4619:Journal of Measurement Science
4544:
4497:
4471:
4443:, Elsevier, pp. 564–587,
4383:Ramsey, Norman F (June 2006).
4376:
4255:
4229:
4017:Time signal radio transmitters
3518:
3512:
2359:Atomic Clock Ensemble in Space
2209:
2203:
2070:
2061:
2039:
2033:
1995:
1989:
1805:
1799:
1492:
1486:
1430:
1424:
1010:atom moves at 510 m/s, a
759:University of Colorado Boulder
1:
9404:10.1103/PhysRevLett.97.020801
9335:10.1109/OGC52961.2021.9654373
7781:Dubé, Pierre (15 July 2019).
6804:"A New Era for Atomic Clocks"
6802:Laura Ost (4 February 2014).
4504:Rabi, I. I. (15 April 1937).
4222:
2326:from the warm chamber walls.
2314:clock and the United States'
2156:{\displaystyle T_{c}/{\tau }}
1906:{\displaystyle d=T_{i}/T_{c}}
773:linked to atomic motion, the
705:to reach greater accuracies.
397:developed a technique called
155:International System of Units
29:Atomic Clock (disambiguation)
14634:
12086:"GNSS Timescale Description"
12060:safran-navigation-timing.com
11620:"UTC to GPS Time Correction"
11529:"The Science of Timekeeping"
11476:; Seidelmann, P. K. (2009).
9792:Ball, Philip (9 July 2013).
7754:Wills, Stewart (July 2019).
7192:"Aluminum ion BIPM document"
6343:La Rivista del Nuovo Cimento
5901:swenson (29 December 1999).
5762:"How Do Atomic Clocks Work?"
5033:; Seidelmann, P. K. (2009).
4744:National Physical Laboratory
3871:navigation satellite systems
2308:National Physical Laboratory
2267:and his colleagues in 1978.
1865:, and where the duty factor
1838:, the interrogation time is
1631:{\displaystyle T_{\text{c}}}
1219:The core of the traditional
763:National Physical Laboratory
433:National Physical Laboratory
372:National Physical Laboratory
354:The accuracy of mechanical,
317:National Physical Laboratory
7:
14790:Internal combustion engines
14767:External combustion engines
14129:Gravitational time dilation
13965:Barycentric Coordinate Time
13532:Geological history of Earth
11502:"Global Positioning System"
11081:"BIPM work programme: Time"
10902:"BIPM work programme: Time"
10471:Ost, Laura (5 March 2018).
10080:Laura Ost (21 April 2015).
9067:National Science Foundation
5234:swenson (4 February 2010).
4101:
3585:, with a natural linewidth
3277:gravitational time dilation
2942:Clock comparison techniques
2751:atomic electron transitions
2336:
2225:
1698:{\displaystyle {\sqrt {N}}}
1674:{\displaystyle \Delta \nu }
1580:{\displaystyle \Delta \nu }
1379:{\displaystyle \Delta \nu }
1107:
1065:
951:BIPM Circular T publication
877:, the Russian Federation's
447:, abbreviated BIH), at the
10:
15107:
13985:Geocentric Coordinate Time
13970:Barycentric Dynamical Time
13908:Coordinated Universal Time
12884:Orders of magnitude (time)
12612:10.1038/s41586-021-04349-7
11685:. May 2017. Archived from
11139:10.1038/s41586-024-07225-2
10793:10.1038/s41586-021-04344-y
10610:10.1007/s10291-021-01113-2
9061:D. Lindley (20 May 2009).
8996:10.1038/s41586-021-03253-4
8545:10.1038/s41586-024-07839-6
7876:10.1038/s41598-018-26365-w
7427:10.1109/TUFFC.2016.2524988
7123:10.1103/PhysRevA.68.052503
6779:. nist.gov. 3 April 2014.
6155:NCSL International Measure
5476:10.1038/s41586-021-04349-7
4927:10.1142/9789812795717_0015
4848:"History of Atomic Clocks"
4401:10.1088/0026-1394/42/3/s01
4333:10.1088/0026-1394/51/3/174
4020:
3926:(GLONASS) operated by the
3873:, and applications in the
3632:A definition based on the
3380:U.S. Department of Defense
2734:
2661:
2259:, which was introduced by
1223:atomic clock is a tunable
1167:
1111:
1102:GPS disciplined oscillator
1069:
999:clock, developed in 2013.
977:
973:
669:scientists demonstrated a
303:
18:
15081:Electronic test equipment
15042:
14991:
14973:
14930:
14892:
14844:
14821:
14788:
14765:
14718:
14685:
14644:Classical simple machines
14642:
14539:
14430:
14397:
14371:
14252:
14152:
14139:Time-translation symmetry
14069:
14043:
14026:
13950:International Atomic Time
13900:
13877:
13807:
13781:
13775:Electric clock technology
13713:
13655:
13608:
13595:Time translation symmetry
13540:
13480:
13470:
13392:
13319:
13239:
13180:
13064:
12982:
12892:
12854:
12840:
12809:
12339:"Deep Space Atomic Clock"
12253:. BBC. 27 December 2012.
12227:. BBC. 27 December 2011.
11918:. European Space Agency.
11799:. European Space Agency.
11735:"Time References in GNSS"
11538:(1289). Hewlett Packard.
11504:. Gps.gov. Archived from
11059:10.1103/RevModPhys.87.637
11029:Reviews of Modern Physics
10880:10.1393/ncr/i2013-10095-x
10850:Rivista del Nuovo Cimento
10736:10.1038/s41586-018-0738-2
10539:10.1038/s41586-020-3006-1
10150:Systematic Uncertainty".
9806:10.1038/nature.2013.13363
9592:"Ytterbium BIPM document"
9292:10.1038/s42005-019-0249-y
8269:10.1038/s41586-019-1533-4
8205:10.1038/s41586-019-1542-3
8141:10.1038/s41586-018-0011-8
7944:10.1209/epl/i2003-00210-x
7160:"Strontium BIPM document"
7063:10.1088/0026-1394/9/3/004
6517:10.1088/1464-4266/5/2/373
6373:10.1393/ncr/i2013-10095-x
6320:10.1103/RevModPhys.87.637
6289:Reviews of Modern Physics
6262:10.1393/ncr/i2013-10095-x
6232:Rivista del Nuovo Cimento
5927:mweiss (26 August 2009).
5210:"Optical Frequency Combs"
5208:NIST (31 December 2009).
5180:10.1109/JSTQE.2003.819109
4335:(inactive 23 June 2024).
3904:United States Space Force
3900:Global Positioning System
3404:beams. These clocks have
3163:electromagnetic radiation
3161:. The color of a clock's
1098:global positioning system
931:International Atomic Time
913:International timekeeping
562:to measure time precisely
437:International Time Bureau
429:National Research Council
214:International Atomic Time
151:electromagnetic radiation
103:
93:
79:
65:
55:
43:
38:
15091:Time measurement systems
12801:
9329:. IEEE. pp. 92–95.
8497:(10)</sys> eV
7596:5 September 2010 at the
7007:"Rubidium BIPM document"
5567:10.1088/1681-7575/ad17d2
5120:10.1088/1681-7575/ab3a82
3989:Experimental space clock
3601:{\displaystyle \Delta f}
3386:Chip-scale atomic clocks
3363:(BIPM) for establishing
2962:lab and its partner lab
1949:can be approximated as
1749:{\displaystyle \nu _{0}}
1352:{\displaystyle \nu _{0}}
1159:Time measuring mechanism
1143:tests of the effects of
968:
653:Chip-scale atomic clocks
558:lattice clock that uses
482:Definition of the second
474:. In 1964, engineers at
292:, measures time with an
255:is (a timing error of a
27:. For other topics, see
15029:Check weighing machines
14399:Astronomical chronology
14372:Archaeology and geology
14079:Absolute space and time
13995:IERS Reference Meridian
13990:International Date Line
13901:International standards
13550:Absolute space and time
13201:Astronomical chronology
11828:. European Commission.
11527:David W. Allan (1997).
11394:National Science Review
11210:Physical Review Letters
11105:"Optical Clocks at Sea"
11006:10.1364/OPTICA.3.000563
10641:Physical Review Letters
10396:Physical Review Letters
10252:10.1126/science.aam5538
10152:Physical Review Letters
9740:Joint Quantum Institute
9383:Physical Review Letters
9198:10.1126/science.aay3676
8672:Physical Review Letters
8413:Physical Review Letters
8340:Physical Review Letters
7695:Physical Review Letters
7619:Physical Review Letters
7600:, NIST, 4 February 2010
7461:www.laserfocusworld.com
7314:Physical Review Letters
7223:Physical Review Letters
6973:"Unit of time (second)"
6958:10.1126/science.aat4586
6861:National Science Review
6560:10.1109/TUFFC.2010.1457
6225:"Optical Atomic Clocks"
5381:Physical Review Letters
4270:. National Public Radio
3995:Deep Space Atomic Clock
3961:hydrogen maser and two
3840:quantum electrodynamics
3487:{\displaystyle \sigma }
1770:Flicker frequency noise
1227:containing a gas. In a
1215:Tuning and optimization
1201:2019 revision of the SI
1153:gravitational red shift
943:equal gravity potential
881:, the European Union's
671:chip-scale atomic clock
572:optical frequency combs
435:in the United Kingdom,
323:The Scottish physicist
243:and the United States'
157:' (SI) definition of a
13782:Powerline synchronized
13600:Time reversal symmetry
12904:Italian six-hour clock
12699:"Keeping Time at NIST"
12505:7 January 2021 at the
11345:10.1098/rsta.2011.0237
11291:10.1098/rsta.2011.0237
9262:Communications Physics
6146:NIST (December 2007).
5649:7 January 2021 at the
5641:Available on-line at:
5627:. 2007. Archived from
5591:. 2011. Archived from
4652:D.B. Sullivan (2001).
4578:10.1103/physrev.53.318
4530:10.1103/physrev.51.652
4268:Weekend Edition Sunday
4092:high-frequency trading
4068:gravitational redshift
4056:gravitational redshift
3939:
3902:(GPS) operated by the
3824:
3759:
3602:
3572:
3488:
3468:
3296:
3183:University of Delaware
3177:
3053:Nobel Prize in Physics
3035:
2717:optical lattice clocks
2350:
2238:
2216:
2157:
2117:
1939:
1907:
1859:
1832:
1812:
1750:
1723:
1699:
1675:
1652:
1632:
1605:
1581:
1555:
1437:
1380:
1353:
1123:
1081:
1028:
922:
909:of a few nanoseconds.
709:How atomic clocks work
662:
563:
468:National Radio Company
466:During the 1950s, the
453:National Radio Company
427:(PTB) in Germany, the
407:Claude Cohen-Tannoudji
386:
320:
210:
189:
130:
119:U.S. Naval Observatory
15014:Seed-counting machine
14358:Weekday determination
14244:Sundial markup schema
13365:Time and fate deities
13310:The Unreality of Time
13249:A series and B series
12498:Michael A. Lombardi,
9992:Nature Communications
9094:(29 September 2020).
8882:Nature Communications
8556:ground state and the
8314:10.1103/Physics.17.71
7800:10.1103/physics.12.79
5274:Nature Communications
5003:Forman, Paul (1998).
4145:Network Time Protocol
4140:List of atomic clocks
3955:European Space Agency
3937:
3825:
3760:
3603:
3573:
3489:
3469:
3395:Redefining the second
3293:
3171:
3124:magneto-optical traps
3029:
2662:Further information:
2344:
2233:
2217:
2158:
2118:
1940:
1908:
1860:
1858:{\displaystyle T_{i}}
1833:
1831:{\displaystyle \tau }
1813:
1751:
1724:
1722:{\displaystyle \tau }
1707:signal to noise ratio
1700:
1676:
1653:
1651:{\displaystyle \tau }
1633:
1606:
1582:
1556:
1438:
1381:
1354:
1323:regime and higher).
1121:
1079:
1041:frequency synthesizer
1026:
920:
800:at a specific point.
729:A number of national
660:
553:
431:(NRC) in Canada, the
414:Ramsey interferometry
384:
311:
190:
163:
116:
14813:Nutating disc engine
14803:Reciprocating engine
14379:Chronological dating
14119:Theory of relativity
13980:Daylight saving time
13616:Chronological dating
13585:Theory of relativity
12929:Daylight saving time
12643:(16 February 2022).
11447:(11 February 2010).
11175:www.businesswire.com
10061:on 19 September 2015
8648:(4 September 2024).
6748:"Second: The Future"
5707:(11 December 2019).
5064:Smithsonian Magazine
4864:10.6028/jres.088.015
4823:. 15 November 2013.
3951:European GNSS Agency
3769:
3640:
3589:
3506:
3478:
3420:
2672:based on individual
2349:-based optical clock
2324:black-body radiation
2167:
2130:
1956:
1917:
1869:
1842:
1822:
1776:
1733:
1713:
1685:
1681:is smaller and when
1662:
1642:
1615:
1595:
1568:
1450:
1411:
1367:
1336:
1295:, the swinging of a
1231:clock the gas emits
1135:, in particular for
1045:hyperfine transition
777:of the environment (
530:decided upon at the
336:, which defines the
169:
88:satellite navigation
14589:Time value of money
14384:Geologic time scale
14239:History of sundials
14104:Cosmological decade
14056:Greenwich Mean Time
13887:Orders of magnitude
12909:Thai six-hour clock
12604:2022Natur.602..420B
12521:"Radio Station WWV"
12475:Airforce Technology
11942:"Galileo Goes Live"
11406:10.1093/nsr/nwaa215
11337:2011RSPTA.369.4109G
11331:(1953): 4109–4130.
11283:2011RSPTA.369.4109G
11277:(1953): 4109–4130.
11131:2024Natur.628..736R
11051:2015RvMP...87..637L
10998:2016Optic...3..563G
10944:2014NatPh..10...82M
10872:2013NCimR..36..555P
10785:2022Natur.602..425Z
10728:2018Natur.564...87M
10602:2021GPSS...25...83S
10531:2020Natur.588..414P
10419:2018PhRvL.120j3201M
10277:on 15 December 2019
10244:2017Sci...358...90C
10174:2016PhRvL.116f3001H
10014:2015NatCo...6.6896N
9934:10.1038/nature12941
9926:2014Natur.506...71B
9544:2021OExpr..2936734G
9538:(22): 36734–36744.
9396:2006PhRvL..97b0801O
9284:2019CmPhy...2..153F
9190:2020Sci...369..367D
9153:. 29 September 2020
8988:2021Natur.591..564B
8912:10.1038/ncomms12443
8904:2016NatCo...712443L
8845:2015Natur.522...16G
8796:2015Natur.522...16G
8695:2017PhRvL.118d2501S
8379:148.3821(5) nm
8353:2024PhRvL.132r2501T
8261:2019Natur.573..243S
8197:2019Natur.573..238M
8133:2018Natur.556..321T
8079:10.1038/nature17669
8071:2016Natur.533...47V
8007:2012PhRvL.108l0802C
7961:on 16 December 2013
7936:2003EL.....61..181P
7924:Europhysics Letters
7868:2018NatSR...8.8022G
7717:2019PhRvL.123c3201B
7641:2010PhRvL.104g0802C
7336:2016PhRvL.116f3001H
7245:2019PhRvL.123c3201B
7115:2003PhRvA..68e2503D
7055:1973Metro...9..128E
6874:10.1093/nsr/nwaa215
6509:2003JOptB...5S.150Q
6409:Dick, G.J. (1987).
6365:2013NCimR..36..555P
6312:2015RvMP...87..637L
6254:2013NCimR..36..555P
6186:2021RScI...92l4705J
5766:www.timeanddate.com
5735:(29 October 2016).
5709:"Chip-Scale Clocks"
5679:(2 December 2020).
5468:2022Natur.602..420B
5296:2015NatCo...6.6896N
5172:2003IJSTQ...9.1041Y
5112:2019Metro..56e5009L
4974:1978PhT....31l..23H
4786:1955Natur.176..280E
4710:1955Natur.176..280E
4569:1938PhRv...53..318R
4522:1937PhRv...51..652R
4435:Achard, F. (2005),
4237:"USNO Master Clock"
4194:Researchers at the
3949:is operated by the
3842:/QED calculations.
3698:
3233:age of the universe
3062:The development of
2868:internal conversion
2670:quantum logic clock
2421: by definition
2382:Working frequency (
2284:age of the universe
2022:
1913:has typical values
1798:
991:clocks include the
885:system and China's
790:gravitational field
325:James Clerk Maxwell
14836:Peaucellier-Lipkin
14564:Mental chronometry
14192:Marine chronometer
14044:Obsolete standards
13439:Rosy retrospection
13417:Mental chronometry
13241:Philosophy of time
12318:on 28 October 2020
12153:The New York Times
11916:"Galileo's clocks"
11177:. 13 November 2023
10022:10.1038/ncomms7896
9988:total uncertainty"
9872:. 27 August 2013.
9846:. 22 August 2013.
9234:. 18 December 2009
7856:Scientific Reports
7836:10.3390/app8112194
7515:. 16 December 2020
6691:. 23 December 2016
5304:10.1038/ncomms7896
5270:total uncertainty"
5011:on 21 October 2007
4116:Electronics portal
4082:at the same time.
4052:General relativity
4047:General relativity
3940:
3820:
3755:
3684:
3598:
3568:
3484:
3464:
3297:
3185:in December 2012.
3178:
3086:around the world.
3036:
2781:based on a single
2749:) rather than the
2351:
2239:
2212:
2153:
2113:
2003:
1935:
1903:
1855:
1828:
1818:is independent of
1808:
1779:
1746:
1719:
1695:
1671:
1648:
1628:
1601:
1577:
1551:
1433:
1376:
1349:
1269:experimental error
1265:quantum-mechanical
1247:Doppler broadening
1149:general relativity
1145:special relativity
1124:
1082:
1029:
963:fiber-optic cables
923:
907:general relativity
903:special relativity
794:general relativity
663:
564:
403:magnetic resonance
387:
351:frequency clocks.
349:magnetic resonance
321:
247:. The timekeeping
233:satellite networks
185:
131:
70:Telecommunications
15058:
15057:
15034:Riveting machines
14732:Archimedes' screw
14602:
14601:
14412:Nuclear timescale
14094:Continuous signal
13833:
13832:
13799:Synchronous motor
13794:Utility frequency
13741:
13740:
13651:
13650:
13626:Circadian rhythms
13444:Tense–aspect–mood
13299:Temporal finitism
13176:
13175:
13152:Grandfather clock
12761:978-1-939133-01-4
12676:. 25 October 2021
12588:(7897): 420–424.
12477:. 21 January 2022
12451:. 1 February 2022
12006:on 26 August 2019
11864:on 9 January 2017
11487:978-3-527-40780-4
11400:(12): 1828–1836.
11115:(8009): 736–740.
10952:10.1038/nphys2834
10769:(7897): 425–430.
10515:(7838): 414–418.
9742:. 5 December 2012
9553:10.1364/OE.435105
9421:on 17 April 2007.
9344:978-1-6654-3194-1
9035:(24 March 2021).
8982:(7851): 564–569.
8731:has been measured
8245:(7773): 243–246.
8181:(7773): 238–242.
8117:(7701): 321–325.
7093:Physical Review A
6867:(12): 1828–1836.
6460:10.1109/58.710548
6194:10.1063/5.0061727
5864:978-92-822-2280-5
5631:on 7 January 2008
5520:. 18 October 2021
5452:(7897): 420–424.
5044:978-3-527-40780-4
4982:10.1063/1.2994867
4936:978-981-02-3250-4
4915:, 541–552 (1990)"
4704:(4476): 280–282.
4667:. pp. 4–17.
4182:Explanatory notes
4086:Financial systems
4080:quantum mechanics
4041:radio transmitter
3974:BeiDou-2/BeiDou-3
3818:
3753:
3713:
3566:
3563:
3462:
3442:
3210:Paris Observatory
3057:David J. Wineland
3049:Theodor W. Hänsch
2968:Boulder, Colorado
2890:ionization energy
2848:Although neutral
2651:
2650:
2394:(typical clocks)
2274:to accuracies of
2108:
2107:
2082:
2043:
2042:
1693:
1625:
1604:{\displaystyle N}
1546:
1545:
1539:
1527:
1524:
1301:grandfather clock
1263:In this way, the
1207:and almost every
1072:Rubidium standard
775:thermal radiation
735:Paris Observatory
449:Paris Observatory
356:electromechanical
345:Isidor Isaac Rabi
340:for timekeeping.
338:mean solar second
241:Galileo Programme
182:
111:
110:
15098:
14737:Eductor-jet pump
14629:
14622:
14615:
14606:
14605:
14303:Dominical letter
14234:Equation of time
14197:Marine sandglass
14038:
14032:
14010:Terrestrial Time
13867:Time measurement
13860:
13853:
13846:
13837:
13836:
13768:
13761:
13754:
13745:
13744:
13731:
13730:
13721:
13720:
13638:Glottochronology
13478:
13477:
13394:Human experience
13254:B-theory of time
12852:
12851:
12796:
12789:
12782:
12773:
12772:
12766:
12765:
12745:
12739:
12738:
12736:
12734:
12720:
12714:
12713:
12711:
12709:
12697:(18 June 2020).
12692:
12686:
12685:
12683:
12681:
12666:
12660:
12659:
12657:
12655:
12638:
12632:
12631:
12597:
12576:
12570:
12569:
12567:
12565:
12542:
12536:
12535:
12533:
12531:
12516:
12510:
12496:
12487:
12486:
12484:
12482:
12467:
12461:
12460:
12458:
12456:
12449:The Defense Post
12441:
12435:
12434:
12432:
12430:
12415:
12409:
12408:
12406:
12404:
12393:
12387:
12386:
12384:
12382:
12367:
12361:
12360:
12358:
12356:
12334:
12328:
12327:
12325:
12323:
12304:
12298:
12297:
12295:
12293:
12273:
12267:
12266:
12264:
12262:
12247:
12241:
12240:
12238:
12236:
12221:
12215:
12214:
12212:
12210:
12204:
12197:
12189:
12183:
12178:
12172:
12171:
12169:
12167:
12144:
12138:
12137:
12135:
12133:
12128:on 28 March 2018
12124:. Archived from
12114:
12108:
12107:
12105:
12103:
12097:
12090:
12082:
12076:
12075:
12073:
12071:
12052:
12046:
12045:
12043:
12041:
12022:
12016:
12015:
12013:
12011:
12002:. Archived from
11996:
11990:
11989:
11987:
11985:
11979:
11972:
11964:
11958:
11957:
11955:
11953:
11938:
11932:
11931:
11929:
11927:
11912:
11906:
11905:
11903:
11901:
11895:
11888:
11880:
11874:
11873:
11871:
11869:
11863:
11857:. Archived from
11856:
11848:
11842:
11841:
11839:
11837:
11822:
11813:
11812:
11810:
11808:
11793:
11787:
11786:
11784:
11782:
11776:
11769:
11761:
11755:
11754:
11752:
11750:
11731:
11725:
11724:
11722:
11720:
11705:
11699:
11698:
11696:
11694:
11679:
11673:
11671:
11669:
11667:
11661:
11654:
11646:
11640:
11639:
11637:
11635:
11616:
11610:
11609:
11607:
11605:
11590:
11584:
11583:
11581:
11579:
11573:
11562:
11553:
11547:
11546:
11544:
11536:Application Note
11533:
11524:
11518:
11517:
11515:
11513:
11498:
11492:
11491:
11470:
11464:
11463:
11461:
11459:
11442:
11436:
11435:
11425:
11385:
11379:
11378:
11371:
11365:
11364:
11320:
11311:
11310:
11266:
11260:
11259:
11225:
11205:
11203:
11193:
11187:
11186:
11184:
11182:
11167:
11161:
11160:
11150:
11124:
11099:
11093:
11092:
11090:
11088:
11077:
11071:
11070:
11044:
11024:
11018:
11017:
10991:
10970:
10964:
10963:
10924:
10918:
10917:
10915:
10913:
10898:
10892:
10891:
10865:
10845:
10839:
10838:
10836:
10834:
10819:
10813:
10812:
10778:
10754:
10748:
10747:
10721:
10697:
10691:
10690:
10656:
10636:
10628:
10622:
10621:
10587:
10577:
10571:
10570:
10568:
10566:
10524:
10499:
10493:
10492:
10490:
10488:
10468:
10462:
10461:
10459:
10457:
10451:
10412:
10392:
10383:
10377:
10376:
10374:
10372:
10352:
10346:
10345:
10343:
10341:
10326:
10320:
10319:
10317:
10315:
10293:
10287:
10286:
10284:
10282:
10276:
10270:. Archived from
10237:
10217:
10208:
10202:
10201:
10167:
10149:
10147:
10139:
10133:
10132:
10130:
10128:
10108:
10102:
10101:
10099:
10097:
10077:
10071:
10070:
10068:
10066:
10057:. Archived from
10050:
10044:
10043:
10033:
10007:
9987:
9985:
9975:
9969:
9968:
9966:
9964:
9958:
9919:
9901:
9892:
9886:
9885:
9883:
9881:
9866:
9860:
9859:
9857:
9855:
9836:
9830:
9829:
9827:
9825:
9789:
9783:
9782:
9780:
9778:
9758:
9752:
9751:
9749:
9747:
9732:
9726:
9725:
9723:
9721:
9706:
9700:
9699:
9697:
9695:
9672:
9666:
9665:
9663:
9661:
9646:
9640:
9639:
9637:
9635:
9620:
9614:
9613:
9611:
9609:
9603:
9596:
9588:
9582:
9581:
9555:
9523:
9517:
9516:
9514:
9502:
9496:
9495:
9493:
9491:
9469:
9460:
9459:
9457:
9455:
9449:
9443:. Archived from
9438:
9429:
9423:
9422:
9420:
9414:. Archived from
9379:
9370:
9357:
9356:
9318:
9312:
9311:
9277:
9253:
9244:
9243:
9241:
9239:
9224:
9218:
9217:
9169:
9163:
9162:
9160:
9158:
9143:
9137:
9136:
9134:
9132:
9117:
9111:
9110:
9108:
9106:
9089:
9083:
9082:
9080:
9078:
9058:
9052:
9051:
9049:
9047:
9030:
9024:
9023:
8966:
8960:
8959:
8957:
8955:
8940:
8934:
8933:
8923:
8897:
8873:
8867:
8866:
8856:
8824:
8818:
8817:
8807:
8775:
8769:
8768:
8766:
8764:
8758:
8751:
8740:
8734:
8733:
8730:
8728:
8688:
8666:
8660:
8659:
8642:
8636:
8635:
8632:
8631:
8629:
8626:
8623:
8620:
8586:
8584:
8583:
8580:
8577:
8562:
8555:
8538:
8512:
8506:
8505:
8498:
8492:
8486:
8474:
8464:
8461:
8455:
8445:
8429:
8406:
8400:
8399:
8396:
8392:
8388:
8387:.409(7) THz
8386:
8380:
8336:
8327:
8318:
8317:
8308:. Vol. 17.
8295:
8289:
8288:
8254:
8231:
8225:
8224:
8190:
8167:
8161:
8160:
8126:
8105:
8099:
8098:
8064:
8041:
8035:
8034:
8000:
7980:
7971:
7970:
7968:
7966:
7960:
7954:. Archived from
7921:
7912:
7906:
7905:
7895:
7847:
7841:
7840:
7838:
7823:Applied Sciences
7820:
7811:
7805:
7804:
7802:
7778:
7772:
7771:
7769:
7767:
7751:
7745:
7744:
7710:
7690:
7684:
7683:
7681:
7679:
7673:
7634:
7616:
7607:
7601:
7588:
7582:
7581:
7579:
7577:
7557:
7551:
7550:
7548:
7546:
7531:
7525:
7524:
7522:
7520:
7505:
7499:
7498:
7496:
7494:
7479:
7473:
7472:
7470:
7468:
7463:. September 2001
7453:
7447:
7446:
7420:
7396:
7390:
7389:
7387:
7385:
7370:
7364:
7363:
7329:
7305:
7299:
7298:
7296:
7294:
7279:
7273:
7272:
7238:
7214:
7208:
7207:
7205:
7203:
7188:
7182:
7181:
7179:
7177:
7171:
7164:
7156:
7150:
7149:
7147:
7145:
7139:
7108:
7106:quant-ph/0308136
7090:
7081:
7075:
7074:
7035:
7029:
7028:
7026:
7024:
7018:
7011:
7003:
6997:
6996:
6994:
6992:
6969:
6963:
6962:
6960:
6940:
6934:
6933:
6931:
6929:
6923:
6912:
6903:
6897:
6896:
6886:
6876:
6852:
6846:
6845:
6843:
6830:
6824:
6823:
6821:
6819:
6799:
6793:
6792:
6790:
6788:
6769:
6763:
6762:
6760:
6758:
6746:(9 April 2019).
6741:
6735:
6734:
6732:
6730:
6707:
6701:
6700:
6698:
6696:
6681:
6675:
6674:
6672:
6670:
6656:
6650:
6649:
6647:
6645:
6630:
6624:
6623:
6621:
6619:
6612:Revolutionalized
6604:
6598:
6597:
6589:
6580:
6579:
6553:
6527:
6521:
6520:
6503:(2): S150–S154.
6486:
6480:
6479:
6441:
6435:
6426:
6420:
6419:
6417:
6406:
6400:
6391:
6385:
6384:
6358:
6338:
6332:
6331:
6305:
6283:
6274:
6273:
6247:
6229:
6220:
6214:
6213:
6169:
6163:
6162:
6152:
6143:
6137:
6136:
6135:
6133:
6127:
6111:(8th ed.),
6110:
6096:
6090:
6089:
6081:
6075:
6074:
6072:
6070:
6065:
6057:
6051:
6050:
6048:
6046:
6031:
6025:
6024:
6022:
6020:
6005:
5999:
5998:
5996:
5994:
5985:. 3 April 2014.
5975:
5969:
5968:
5966:
5964:
5958:www.grc.nasa.gov
5950:
5944:
5943:
5941:
5939:
5924:
5918:
5917:
5915:
5913:
5898:
5892:
5891:
5889:
5887:
5881:
5856:
5846:
5840:
5839:
5838:
5836:
5830:
5824:, 12 July 2021,
5819:
5809:
5803:
5802:
5796:
5788:
5777:
5776:
5774:
5772:
5758:
5752:
5751:
5749:
5747:
5730:
5724:
5723:
5721:
5719:
5702:
5696:
5695:
5693:
5691:
5674:
5668:
5667:
5659:
5653:
5640:
5638:
5636:
5617:
5608:
5607:
5605:
5603:
5597:
5590:
5582:
5571:
5570:
5560:
5536:
5530:
5529:
5527:
5525:
5510:
5504:
5503:
5461:
5437:
5431:
5430:
5396:
5376:
5368:
5362:
5361:
5359:
5357:
5345:(15 July 2019).
5340:
5334:
5333:
5323:
5289:
5269:
5267:
5257:
5251:
5250:
5248:
5246:
5231:
5225:
5224:
5222:
5220:
5205:
5199:
5198:
5196:
5194:
5188:
5166:(4): 1041–1058.
5155:
5146:
5140:
5139:
5105:
5081:
5075:
5074:
5072:
5070:
5055:
5049:
5048:
5027:
5021:
5020:
5018:
5016:
5007:. Archived from
5000:
4994:
4993:
4953:
4947:
4946:
4945:
4943:
4900:
4894:
4893:
4883:
4843:
4837:
4836:
4834:
4832:
4821:ESO Announcement
4813:
4807:
4805:
4794:10.1038/176280a0
4766:
4760:
4759:
4757:
4755:
4736:
4730:
4729:
4718:10.1038/176280a0
4690:
4684:
4683:
4681:
4679:
4673:
4658:
4649:
4643:
4642:
4640:
4638:
4632:
4615:
4606:
4591:
4590:
4580:
4548:
4542:
4541:
4501:
4495:
4494:
4492:
4490:
4475:
4469:
4468:
4467:
4465:
4432:
4421:
4420:
4380:
4374:
4373:
4367:
4359:
4356:
4352:
4350:
4344:
4342:
4316:
4307:
4298:
4297:
4286:
4280:
4279:
4277:
4275:
4259:
4253:
4252:
4250:
4248:
4233:
4216:
4214:
4212:
4205:
4199:
4192:
4125:Caesium standard
4118:
4113:
4112:
4077:
4075:
4012:
3837:
3829:
3827:
3826:
3821:
3819:
3817:
3816:
3807:
3800:
3799:
3789:
3781:
3780:
3764:
3762:
3761:
3756:
3754:
3752:
3744:
3743:
3742:
3730:
3729:
3719:
3714:
3712:
3708:
3707:
3697:
3692:
3679:
3678:
3677:
3668:
3667:
3657:
3652:
3651:
3634:Rydberg constant
3628:Rydberg constant
3623:
3619:
3611:
3607:
3605:
3604:
3599:
3584:
3577:
3575:
3574:
3569:
3567:
3565:
3564:
3559:
3558:
3540:
3525:
3493:
3491:
3490:
3485:
3473:
3471:
3470:
3465:
3463:
3461:
3457:
3445:
3443:
3438:
3430:
3411:
3409:
3350:
3348:
3338:
3336:
3323:
3321:
3315:
3313:
3307:
3305:
3274:
3272:
3258:
3254:
3251:atoms cooled to
3250:
3249:10 000 ytterbium
3246:
3242:
3240:
3226:
3224:
3207:
3205:
3195:
3193:
3091:femtosecond comb
3071:optical lattices
3017:
3015:
2998:
2996:
2982:
2980:
2953:
2935:Mössbauer effect
2913:
2909:
2908:
2907:
2900:
2899:
2887:
2886:
2885:
2878:
2877:
2865:
2864:
2863:
2856:
2855:
2844:
2842:
2838:
2835:
2832:
2826:
2824:
2821:
2818:
2815:
2812:
2806:
2804:
2798:
2797:
2796:
2789:
2788:
2772:
2770:
2769:
2762:
2761:
2711:
2709:
2700:
2698:
2645:
2640:
2638:
2635:
2632:
2629:
2626:
2608:
2603:
2601:
2598:
2595:
2592:
2589:
2571:
2566:
2564:
2561:
2558:
2555:
2552:
2549:
2531:
2526:
2524:
2521:
2518:
2515:
2512:
2494:
2489:
2487:
2484:
2481:
2478:
2462:
2457:
2455:
2452:
2449:
2446:
2443:
2427:
2419:
2417:
2414:
2411:
2376:
2375:
2371:available online
2345:An experimental
2331:published online
2312:caesium fountain
2305:
2281:
2277:
2273:
2261:Jerrod Zacharias
2257:caesium fountain
2254:
2250:
2221:
2219:
2218:
2213:
2202:
2201:
2200:
2199:
2162:
2160:
2159:
2154:
2152:
2147:
2142:
2141:
2122:
2120:
2119:
2114:
2109:
2103:
2102:
2093:
2092:
2087:
2083:
2081:
2073:
2053:
2044:
2023:
2021:
2020:
2011:
2002:
1988:
1987:
1986:
1985:
1944:
1942:
1941:
1936:
1912:
1910:
1909:
1904:
1902:
1901:
1892:
1887:
1886:
1864:
1862:
1861:
1856:
1854:
1853:
1837:
1835:
1834:
1829:
1817:
1815:
1814:
1809:
1797:
1796:
1787:
1766:local oscillator
1755:
1753:
1752:
1747:
1745:
1744:
1728:
1726:
1725:
1720:
1704:
1702:
1701:
1696:
1694:
1689:
1680:
1678:
1677:
1672:
1657:
1655:
1654:
1649:
1637:
1635:
1634:
1629:
1627:
1626:
1623:
1610:
1608:
1607:
1602:
1586:
1584:
1583:
1578:
1560:
1558:
1557:
1552:
1547:
1541:
1540:
1537:
1531:
1530:
1528:
1526:
1525:
1520:
1518:
1517:
1507:
1499:
1485:
1484:
1483:
1482:
1442:
1440:
1439:
1434:
1423:
1422:
1391:
1385:
1383:
1382:
1377:
1358:
1356:
1355:
1350:
1348:
1347:
1331:
1281:local oscillator
1225:microwave cavity
1187:
1185:
1182:
1179:
1122:A hydrogen maser
1095:
1093:
1054:
1052:
980:Caesium standard
936:
850:
846:
838:
834:
826:
822:
818:
784:
679:
648:
646:
640:
638:
632:
628:
626:
617:
615:
609:
598:. Scientists at
581:
540:Rydberg constant
509:
507:
504:
498:
497:
494:
491:
334:Earth's rotation
299:
276:atoms cooled to
268:
267:
263:
226:Earth's rotation
207:
206:
203:
200:
194:
192:
191:
186:
184:
183:
180:
123:Washington, D.C.
48:
36:
35:
15106:
15105:
15101:
15100:
15099:
15097:
15096:
15095:
15061:
15060:
15059:
15054:
15050:Spring (device)
15038:
15019:Vending machine
14987:
14969:
14926:
14888:
14840:
14817:
14784:
14780:Stirling engine
14761:
14714:
14681:
14638:
14633:
14603:
14598:
14535:
14426:
14393:
14367:
14248:
14148:
14099:Coordinate time
14071:Time in physics
14065:
14039:
14033:
14024:
13896:
13873:
13864:
13834:
13829:
13803:
13777:
13772:
13742:
13737:
13709:
13700:Time immemorial
13647:
13604:
13565:Coordinate time
13536:
13490:Geological time
13466:
13449:Time management
13412:Generation time
13396:
13388:
13333:
13315:
13235:
13194:
13172:
13060:
12978:
12895:
12888:
12844:
12836:
12805:
12800:
12770:
12769:
12762:
12746:
12742:
12732:
12730:
12728:www.chainzy.com
12722:
12721:
12717:
12707:
12705:
12693:
12689:
12679:
12677:
12674:Quanta Magazine
12668:
12667:
12663:
12653:
12651:
12639:
12635:
12577:
12573:
12563:
12561:
12543:
12539:
12529:
12527:
12517:
12513:
12507:Wayback Machine
12497:
12490:
12480:
12478:
12469:
12468:
12464:
12454:
12452:
12443:
12442:
12438:
12428:
12426:
12416:
12412:
12402:
12400:
12395:
12394:
12390:
12380:
12378:
12368:
12364:
12354:
12352:
12335:
12331:
12321:
12319:
12306:
12305:
12301:
12291:
12289:
12274:
12270:
12260:
12258:
12249:
12248:
12244:
12234:
12232:
12223:
12222:
12218:
12208:
12206:
12202:
12195:
12191:
12190:
12186:
12179:
12175:
12165:
12163:
12145:
12141:
12131:
12129:
12116:
12115:
12111:
12101:
12099:
12095:
12088:
12084:
12083:
12079:
12069:
12067:
12054:
12053:
12049:
12039:
12037:
12024:
12023:
12019:
12009:
12007:
11998:
11997:
11993:
11983:
11981:
11977:
11970:
11966:
11965:
11961:
11951:
11949:
11940:
11939:
11935:
11925:
11923:
11914:
11913:
11909:
11899:
11897:
11893:
11886:
11882:
11881:
11877:
11867:
11865:
11861:
11854:
11850:
11849:
11845:
11835:
11833:
11824:
11823:
11816:
11806:
11804:
11795:
11794:
11790:
11780:
11778:
11774:
11767:
11763:
11762:
11758:
11748:
11746:
11733:
11732:
11728:
11718:
11716:
11715:on 8 April 2013
11707:
11706:
11702:
11692:
11690:
11681:
11680:
11676:
11665:
11663:
11659:
11652:
11648:
11647:
11643:
11633:
11631:
11618:
11617:
11613:
11603:
11601:
11592:
11591:
11587:
11577:
11575:
11571:
11560:
11554:
11550:
11542:
11531:
11525:
11521:
11511:
11509:
11508:on 30 July 2010
11500:
11499:
11495:
11488:
11474:McCarthy, D. D.
11471:
11467:
11457:
11455:
11443:
11439:
11386:
11382:
11373:
11372:
11368:
11321:
11314:
11267:
11263:
11201:
11199:
11194:
11190:
11180:
11178:
11169:
11168:
11164:
11100:
11096:
11086:
11084:
11079:
11078:
11074:
11025:
11021:
10971:
10967:
10928:Margolis, Helen
10925:
10921:
10911:
10909:
10900:
10899:
10895:
10856:(12): 555–624.
10846:
10842:
10832:
10830:
10821:
10820:
10816:
10755:
10751:
10712:(7734): 87–90.
10698:
10694:
10634:
10629:
10625:
10585:
10578:
10574:
10564:
10562:
10500:
10496:
10486:
10484:
10469:
10465:
10455:
10453:
10449:
10390:
10384:
10380:
10370:
10368:
10353:
10349:
10339:
10337:
10328:
10327:
10323:
10313:
10311:
10294:
10290:
10280:
10278:
10274:
10228:(6359): 90–94.
10215:
10209:
10205:
10145:
10143:
10140:
10136:
10126:
10124:
10109:
10105:
10095:
10093:
10078:
10074:
10064:
10062:
10051:
10047:
9983:
9981:
9976:
9972:
9962:
9960:
9956:
9899:
9893:
9889:
9879:
9877:
9868:
9867:
9863:
9853:
9851:
9838:
9837:
9833:
9823:
9821:
9790:
9786:
9776:
9774:
9759:
9755:
9745:
9743:
9734:
9733:
9729:
9719:
9717:
9708:
9707:
9703:
9693:
9691:
9675:Norton, Quinn.
9673:
9669:
9659:
9657:
9648:
9647:
9643:
9633:
9631:
9622:
9621:
9617:
9607:
9605:
9601:
9594:
9590:
9589:
9585:
9524:
9520:
9503:
9499:
9489:
9487:
9471:
9470:
9463:
9453:
9451:
9450:on 23 June 2015
9447:
9436:
9430:
9426:
9418:
9377:
9371:
9360:
9345:
9319:
9315:
9254:
9247:
9237:
9235:
9226:
9225:
9221:
9170:
9166:
9156:
9154:
9145:
9144:
9140:
9130:
9128:
9119:
9118:
9114:
9104:
9102:
9090:
9086:
9076:
9074:
9059:
9055:
9045:
9043:
9031:
9027:
8967:
8963:
8953:
8951:
8942:
8941:
8937:
8874:
8870:
8854:10.1038/522016a
8839:(7554): 16–17.
8825:
8821:
8805:10.1038/522016a
8790:(7554): 16–17.
8776:
8772:
8762:
8760:
8756:
8749:
8741:
8737:
8726:
8724:
8723:A half-life of
8667:
8663:
8643:
8639:
8627:
8624:
8621:
8618:
8616:
8614:
8607:
8600:
8593:
8581:
8578:
8575:
8574:
8572:
8570:
8564:
8557:
8550:
8529:(8028): 63–70.
8513:
8509:
8502:
8496:
8490:
8488:
8484:
8480:
8476:
8472:
8468:
8462:
8459:
8457:
8453:
8449:
8443:
8441:
8407:
8403:
8395:1740(50) s
8394:
8390:
8384:
8382:
8378:
8376:
8334:
8328:
8321:
8296:
8292:
8232:
8228:
8168:
8164:
8106:
8102:
8055:(7601): 47–51.
8042:
8038:
7985:Phys. Rev. Lett
7981:
7974:
7964:
7962:
7958:
7919:
7913:
7909:
7848:
7844:
7818:
7812:
7808:
7779:
7775:
7765:
7763:
7752:
7748:
7691:
7687:
7677:
7675:
7671:
7614:
7608:
7604:
7598:Wayback Machine
7589:
7585:
7575:
7573:
7558:
7554:
7544:
7542:
7532:
7528:
7518:
7516:
7507:
7506:
7502:
7492:
7490:
7480:
7476:
7466:
7464:
7455:
7454:
7450:
7397:
7393:
7383:
7381:
7372:
7371:
7367:
7306:
7302:
7292:
7290:
7281:
7280:
7276:
7215:
7211:
7201:
7199:
7190:
7189:
7185:
7175:
7173:
7169:
7162:
7158:
7157:
7153:
7143:
7141:
7137:
7088:
7082:
7078:
7036:
7032:
7022:
7020:
7016:
7009:
7005:
7004:
7000:
6990:
6988:
6971:
6970:
6966:
6941:
6937:
6927:
6925:
6921:
6910:
6904:
6900:
6853:
6849:
6831:
6827:
6817:
6815:
6800:
6796:
6786:
6784:
6771:
6770:
6766:
6756:
6754:
6742:
6738:
6728:
6726:
6708:
6704:
6694:
6692:
6683:
6682:
6678:
6668:
6666:
6658:
6657:
6653:
6643:
6641:
6631:
6627:
6617:
6615:
6606:
6605:
6601:
6590:
6583:
6528:
6524:
6487:
6483:
6442:
6438:
6427:
6423:
6415:
6407:
6403:
6392:
6388:
6339:
6335:
6284:
6277:
6238:(12): 555–624.
6227:
6221:
6217:
6170:
6166:
6150:
6144:
6140:
6131:
6129:
6125:
6119:
6108:
6097:
6093:
6082:
6078:
6068:
6066:
6063:
6059:
6058:
6054:
6044:
6042:
6032:
6028:
6018:
6016:
6006:
6002:
5992:
5990:
5977:
5976:
5972:
5962:
5960:
5952:
5951:
5947:
5937:
5935:
5925:
5921:
5911:
5909:
5899:
5895:
5885:
5883:
5879:
5865:
5854:
5848:
5847:
5843:
5834:
5832:
5828:
5817:
5811:
5810:
5806:
5794:
5790:
5789:
5780:
5770:
5768:
5760:
5759:
5755:
5745:
5743:
5731:
5727:
5717:
5715:
5703:
5699:
5689:
5687:
5675:
5671:
5660:
5656:
5651:Wayback Machine
5634:
5632:
5619:
5618:
5611:
5601:
5599:
5595:
5588:
5584:
5583:
5574:
5537:
5533:
5523:
5521:
5512:
5511:
5507:
5438:
5434:
5374:
5369:
5365:
5355:
5353:
5341:
5337:
5265:
5263:
5258:
5254:
5244:
5242:
5232:
5228:
5218:
5216:
5206:
5202:
5192:
5190:
5186:
5153:
5147:
5143:
5082:
5078:
5068:
5066:
5056:
5052:
5045:
5031:McCarthy, D. D.
5028:
5024:
5014:
5012:
5001:
4997:
4954:
4950:
4941:
4939:
4937:
4910:Rev. Mod. Phys.
4902:
4901:
4897:
4844:
4840:
4830:
4828:
4815:
4814:
4810:
4767:
4763:
4753:
4751:
4738:
4737:
4733:
4691:
4687:
4677:
4675:
4671:
4656:
4650:
4646:
4636:
4634:
4630:
4613:
4607:
4594:
4557:Physical Review
4549:
4545:
4510:Physical Review
4502:
4498:
4488:
4486:
4477:
4476:
4472:
4463:
4461:
4459:
4433:
4424:
4381:
4377:
4361:
4360:
4354:
4348:
4346:
4340:
4338:
4314:
4308:
4301:
4288:
4287:
4283:
4273:
4271:
4260:
4256:
4246:
4244:
4235:
4234:
4230:
4225:
4220:
4219:
4210:
4208:
4206:
4202:
4193:
4189:
4184:
4179:
4114:
4107:
4104:
4088:
4073:
4071:
4049:
4025:
4019:
4010:
4003:
3991:
3896:
3888:radio astronomy
3867:
3855:
3835:
3812:
3808:
3795:
3791:
3790:
3788:
3776:
3772:
3770:
3767:
3766:
3745:
3738:
3734:
3725:
3721:
3720:
3718:
3703:
3699:
3693:
3688:
3680:
3673:
3669:
3663:
3659:
3658:
3656:
3647:
3643:
3641:
3638:
3637:
3630:
3621:
3617:
3614:optical lattice
3609:
3590:
3587:
3586:
3582:
3548:
3544:
3539:
3529:
3524:
3507:
3504:
3503:
3479:
3476:
3475:
3453:
3449:
3444:
3431:
3429:
3421:
3418:
3417:
3407:
3405:
3397:
3388:
3376:Exercise RIMPAC
3346:
3344:
3334:
3332:
3319:
3317:
3311:
3309:
3303:
3301:
3270:
3268:
3256:
3252:
3248:
3244:
3238:
3236:
3222:
3220:
3203:
3201:
3191:
3189:
3067:frequency combs
3024:
3013:
3011:
2994:
2992:
2978:
2976:
2951:
2944:
2911:
2906:
2904:
2903:
2902:
2898:
2896:
2895:
2894:
2893:
2884:
2882:
2881:
2880:
2876:
2874:
2873:
2872:
2871:
2862:
2860:
2859:
2858:
2854:
2852:
2851:
2850:
2849:
2840:
2836:
2833:
2830:
2828:
2822:
2819:
2816:
2813:
2810:
2808:
2802:
2800:
2795:
2793:
2792:
2791:
2787:
2785:
2784:
2783:
2782:
2768:
2766:
2765:
2764:
2760:
2758:
2757:
2756:
2754:
2747:nuclear isomers
2739:
2733:
2707:
2705:
2696:
2694:
2666:
2660:
2643:
2636:
2633:
2630:
2627:
2624:
2622:
2615:Optical clock (
2606:
2599:
2596:
2593:
2590:
2587:
2585:
2578:Optical clock (
2569:
2562:
2559:
2556:
2553:
2550:
2547:
2545:
2538:Optical clock (
2529:
2522:
2519:
2516:
2513:
2510:
2508:
2501:Optical clock (
2492:
2485:
2482:
2479:
2476:
2474:
2460:
2453:
2450:
2447:
2444:
2441:
2439:
2425:
2415:
2412:
2409:
2407:
2393:
2391:Allan deviation
2367:
2339:
2320:liquid nitrogen
2303:
2296:optical lattice
2279:
2275:
2271:
2252:
2248:
2228:
2183:
2182:
2174:
2170:
2168:
2165:
2164:
2148:
2143:
2137:
2133:
2131:
2128:
2127:
2098:
2094:
2091:
2074:
2054:
2052:
2048:
2013:
2012:
2007:
2001:
1972:
1971:
1963:
1959:
1957:
1954:
1953:
1947:Allan deviation
1918:
1915:
1914:
1897:
1893:
1888:
1882:
1878:
1870:
1867:
1866:
1849:
1845:
1843:
1840:
1839:
1823:
1820:
1819:
1789:
1788:
1783:
1777:
1774:
1773:
1740:
1736:
1734:
1731:
1730:
1714:
1711:
1710:
1688:
1686:
1683:
1682:
1663:
1660:
1659:
1643:
1640:
1639:
1622:
1618:
1616:
1613:
1612:
1596:
1593:
1592:
1569:
1566:
1565:
1536:
1532:
1529:
1519:
1513:
1509:
1508:
1500:
1498:
1466:
1465:
1457:
1453:
1451:
1448:
1447:
1418:
1414:
1412:
1409:
1408:
1406:Allan deviation
1387:
1368:
1365:
1364:
1343:
1339:
1337:
1334:
1333:
1327:
1289:
1287:Clock mechanism
1221:radio frequency
1217:
1183:
1180:
1177:
1175:
1172:
1166:
1161:
1133:radio astronomy
1116:
1110:
1091:
1089:
1074:
1068:
1050:
1048:
1021:
982:
976:
971:
934:
915:
866:
848:
844:
836:
832:
831:is one part in
824:
820:
816:
782:
716:
711:
674:
655:
644:
642:
636:
634:
630:
624:
622:
613:
611:
607:
579:
548:
510:seconds in the
505:
502:
500:
495:
492:
489:
487:
484:
476:Hewlett-Packard
461:Hewlett–Packard
399:optical pumping
319:in west London.
306:
297:
265:
261:
260:
204:
201:
198:
196:
179:
175:
170:
167:
166:
51:
32:
17:
12:
11:
5:
15104:
15094:
15093:
15088:
15083:
15078:
15073:
15056:
15055:
15053:
15052:
15046:
15044:
15040:
15039:
15037:
15036:
15031:
15026:
15021:
15016:
15011:
15006:
15001:
14995:
14993:
14989:
14988:
14986:
14985:
14979:
14977:
14971:
14970:
14968:
14967:
14962:
14957:
14952:
14947:
14942:
14936:
14934:
14928:
14927:
14925:
14924:
14919:
14914:
14909:
14904:
14898:
14896:
14890:
14889:
14887:
14886:
14881:
14879:Wind generator
14876:
14871:
14866:
14861:
14856:
14850:
14848:
14842:
14841:
14839:
14838:
14833:
14827:
14825:
14819:
14818:
14816:
14815:
14810:
14805:
14800:
14794:
14792:
14786:
14785:
14783:
14782:
14777:
14771:
14769:
14763:
14762:
14760:
14759:
14754:
14749:
14744:
14739:
14734:
14728:
14726:
14716:
14715:
14713:
14712:
14707:
14705:Pendulum clock
14702:
14697:
14691:
14689:
14683:
14682:
14680:
14679:
14677:Wheel and axle
14674:
14669:
14664:
14659:
14654:
14652:Inclined plane
14648:
14646:
14640:
14639:
14632:
14631:
14624:
14617:
14609:
14600:
14599:
14597:
14596:
14591:
14586:
14584:Time metrology
14581:
14576:
14571:
14566:
14561:
14560:
14559:
14549:
14543:
14541:
14540:Related topics
14537:
14536:
14534:
14533:
14528:
14523:
14518:
14513:
14508:
14503:
14498:
14493:
14488:
14483:
14478:
14473:
14468:
14463:
14458:
14453:
14448:
14443:
14437:
14435:
14428:
14427:
14425:
14424:
14419:
14414:
14409:
14403:
14401:
14395:
14394:
14392:
14391:
14386:
14381:
14375:
14373:
14369:
14368:
14366:
14365:
14360:
14355:
14350:
14345:
14340:
14335:
14330:
14325:
14320:
14315:
14310:
14305:
14300:
14295:
14290:
14285:
14279:
14274:
14269:
14264:
14258:
14256:
14250:
14249:
14247:
14246:
14241:
14236:
14231:
14229:Dialing scales
14226:
14221:
14216:
14215:
14214:
14204:
14199:
14194:
14189:
14184:
14179:
14174:
14169:
14164:
14158:
14156:
14150:
14149:
14147:
14146:
14141:
14136:
14131:
14126:
14121:
14116:
14111:
14106:
14101:
14096:
14091:
14086:
14081:
14075:
14073:
14067:
14066:
14064:
14063:
14061:Prime meridian
14058:
14053:
14051:Ephemeris time
14047:
14045:
14041:
14040:
14027:
14025:
14023:
14022:
14020:180th meridian
14017:
14012:
14007:
14002:
13997:
13992:
13987:
13982:
13977:
13972:
13967:
13962:
13957:
13952:
13947:
13942:
13937:
13932:
13927:
13922:
13917:
13916:
13915:
13904:
13902:
13898:
13897:
13895:
13894:
13889:
13884:
13878:
13875:
13874:
13863:
13862:
13855:
13848:
13840:
13831:
13830:
13828:
13827:
13822:
13817:
13811:
13809:
13805:
13804:
13802:
13801:
13796:
13791:
13785:
13783:
13779:
13778:
13771:
13770:
13763:
13756:
13748:
13739:
13738:
13736:
13735:
13725:
13714:
13711:
13710:
13708:
13707:
13702:
13697:
13692:
13685:
13680:
13675:
13670:
13665:
13659:
13657:
13653:
13652:
13649:
13648:
13646:
13645:
13643:Time geography
13640:
13635:
13633:Clock reaction
13630:
13629:
13628:
13618:
13612:
13610:
13606:
13605:
13603:
13602:
13597:
13592:
13587:
13582:
13577:
13572:
13567:
13562:
13557:
13552:
13546:
13544:
13538:
13537:
13535:
13534:
13529:
13524:
13523:
13522:
13517:
13512:
13507:
13502:
13497:
13486:
13484:
13475:
13468:
13467:
13465:
13464:
13451:
13446:
13441:
13436:
13435:
13434:
13432:time signature
13429:
13419:
13414:
13409:
13403:
13401:
13390:
13389:
13387:
13386:
13385:
13384:
13374:
13373:
13372:
13362:
13357:
13352:
13347:
13342:
13336:
13334:
13332:
13331:
13326:
13320:
13317:
13316:
13314:
13313:
13306:
13304:Temporal parts
13301:
13296:
13291:
13286:
13281:
13276:
13274:Eternal return
13271:
13266:
13261:
13259:Chronocentrism
13256:
13251:
13245:
13243:
13237:
13236:
13234:
13233:
13228:
13223:
13218:
13213:
13208:
13203:
13197:
13195:
13193:
13192:
13187:
13181:
13178:
13177:
13174:
13173:
13171:
13170:
13169:
13168:
13154:
13149:
13144:
13139:
13138:
13137:
13132:
13131:
13130:
13125:
13115:
13110:
13105:
13100:
13099:
13098:
13088:
13087:
13086:
13070:
13068:
13062:
13061:
13059:
13058:
13051:
13046:
13044:Hindu Panchang
13041:
13036:
13031:
13026:
13021:
13016:
13011:
13010:
13009:
13004:
12999:
12988:
12986:
12980:
12979:
12977:
12976:
12971:
12966:
12961:
12956:
12951:
12946:
12941:
12936:
12931:
12926:
12921:
12916:
12911:
12906:
12900:
12898:
12890:
12889:
12887:
12886:
12881:
12876:
12871:
12866:
12860:
12858:
12849:
12838:
12837:
12835:
12834:
12829:
12824:
12819:
12813:
12811:
12807:
12806:
12799:
12798:
12791:
12784:
12776:
12768:
12767:
12760:
12740:
12715:
12687:
12661:
12633:
12571:
12545:Chen, Sophia.
12537:
12511:
12488:
12462:
12436:
12410:
12388:
12362:
12329:
12299:
12268:
12242:
12216:
12184:
12173:
12139:
12122:insidegnss.com
12109:
12077:
12047:
12017:
11991:
11959:
11933:
11907:
11875:
11843:
11814:
11788:
11756:
11726:
11700:
11689:on 28 May 2017
11674:
11641:
11611:
11585:
11548:
11519:
11493:
11486:
11465:
11437:
11380:
11366:
11312:
11261:
11188:
11162:
11094:
11072:
11019:
10982:(6): 563–569.
10965:
10932:Nature Physics
10919:
10893:
10840:
10814:
10749:
10692:
10623:
10572:
10494:
10463:
10403:(10): 103201.
10378:
10347:
10321:
10288:
10203:
10134:
10103:
10072:
10045:
9998:(6896): 6896.
9970:
9910:(7486): 71–5.
9887:
9861:
9831:
9784:
9753:
9727:
9701:
9667:
9641:
9615:
9583:
9532:Optics Express
9518:
9497:
9461:
9432:Fritz Riehle.
9424:
9358:
9343:
9313:
9245:
9219:
9164:
9138:
9127:. 3 March 2017
9112:
9084:
9053:
9025:
8961:
8935:
8868:
8819:
8770:
8735:
8661:
8646:Conover, Emily
8637:
8612:
8605:
8598:
8591:
8568:
8507:
8500:
8494:
8482:
8478:
8470:
8466:
8451:
8447:
8401:
8391:630(15) s
8374:
8319:
8290:
8226:
8162:
8100:
8036:
7972:
7930:(2): 181–186.
7907:
7842:
7806:
7773:
7746:
7685:
7602:
7583:
7552:
7526:
7500:
7482:Ahmed, Issam.
7474:
7448:
7411:(7): 981–985.
7391:
7365:
7300:
7274:
7209:
7183:
7151:
7076:
7049:(3): 128–137.
7030:
6998:
6964:
6935:
6898:
6847:
6825:
6794:
6764:
6736:
6702:
6676:
6651:
6625:
6614:. 20 July 2021
6599:
6581:
6544:(3): 623–628.
6522:
6481:
6454:(4): 887–894.
6436:
6421:
6401:
6386:
6333:
6296:(2): 637–701.
6275:
6215:
6164:
6138:
6117:
6091:
6076:
6052:
6026:
6000:
5970:
5945:
5919:
5893:
5863:
5841:
5804:
5778:
5753:
5725:
5697:
5669:
5654:
5609:
5598:on 25 May 2013
5572:
5531:
5505:
5432:
5363:
5335:
5252:
5226:
5200:
5141:
5076:
5050:
5043:
5022:
4995:
4948:
4935:
4906:Les Prix Nobel
4895:
4858:(5): 301–320.
4838:
4808:
4761:
4731:
4685:
4644:
4592:
4543:
4516:(8): 652–654.
4496:
4485:. 14 June 2022
4470:
4457:
4422:
4375:
4327:(3): 174–182.
4299:
4281:
4254:
4227:
4226:
4224:
4221:
4218:
4217:
4200:
4186:
4185:
4183:
4180:
4178:
4177:
4172:
4167:
4165:Time metrology
4162:
4160:Speaking clock
4157:
4152:
4147:
4142:
4137:
4132:
4127:
4121:
4120:
4119:
4103:
4100:
4087:
4084:
4048:
4045:
4033:radio receiver
4021:Main article:
4018:
4015:
4002:
4001:Military usage
3999:
3990:
3987:
3895:
3892:
3884:interferometry
3866:
3863:
3854:
3851:
3815:
3811:
3806:
3803:
3798:
3794:
3787:
3784:
3779:
3775:
3751:
3748:
3741:
3737:
3733:
3728:
3724:
3717:
3711:
3706:
3702:
3696:
3691:
3687:
3683:
3676:
3672:
3666:
3662:
3655:
3650:
3646:
3629:
3626:
3597:
3594:
3562:
3557:
3554:
3551:
3547:
3543:
3538:
3535:
3532:
3528:
3523:
3520:
3517:
3514:
3511:
3483:
3460:
3456:
3452:
3448:
3441:
3437:
3434:
3428:
3425:
3396:
3393:
3387:
3384:
3253:10 microkelvin
3116:
3115:
3112:
3109:
3023:
3022:Optical clocks
3020:
2943:
2940:
2939:
2938:
2930:
2926:
2916:quality factor
2905:
2897:
2883:
2875:
2861:
2853:
2794:
2786:
2767:
2759:
2735:Main article:
2732:
2729:
2659:
2658:Quantum clocks
2656:
2649:
2648:
2646:
2641:
2620:
2612:
2611:
2609:
2604:
2583:
2575:
2574:
2572:
2567:
2543:
2535:
2534:
2532:
2527:
2506:
2498:
2497:
2495:
2490:
2472:
2466:
2465:
2463:
2458:
2437:
2431:
2430:
2428:
2423:
2405:
2399:
2398:
2395:
2387:
2380:
2366:
2363:
2338:
2335:
2227:
2224:
2211:
2208:
2205:
2198:
2195:
2192:
2189:
2186:
2180:
2177:
2173:
2151:
2146:
2140:
2136:
2124:
2123:
2112:
2106:
2101:
2097:
2090:
2086:
2080:
2077:
2072:
2069:
2066:
2063:
2060:
2057:
2051:
2047:
2041:
2038:
2035:
2032:
2029:
2026:
2019:
2016:
2010:
2006:
2000:
1997:
1994:
1991:
1984:
1981:
1978:
1975:
1969:
1966:
1962:
1934:
1931:
1928:
1925:
1922:
1900:
1896:
1891:
1885:
1881:
1877:
1874:
1852:
1848:
1827:
1807:
1804:
1801:
1795:
1792:
1786:
1782:
1743:
1739:
1718:
1692:
1670:
1667:
1647:
1621:
1600:
1576:
1573:
1562:
1561:
1550:
1544:
1535:
1523:
1516:
1512:
1506:
1503:
1497:
1494:
1491:
1488:
1481:
1478:
1475:
1472:
1469:
1463:
1460:
1456:
1432:
1429:
1426:
1421:
1417:
1375:
1372:
1346:
1342:
1288:
1285:
1229:hydrogen maser
1216:
1213:
1168:Main article:
1165:
1162:
1160:
1157:
1114:Hydrogen maser
1112:Main article:
1109:
1106:
1100:receiver (see
1070:Main article:
1067:
1064:
1053:.6317 MHz
1020:
1017:
978:Main article:
975:
972:
970:
967:
947:rotating geoid
914:
911:
865:
862:
771:Doppler shifts
715:
714:Time standards
712:
710:
707:
654:
651:
547:
544:
536:optical clocks
483:
480:
391:Alfred Kastler
305:
302:
280:that approach
253:speed of light
237:European Union
178:
174:
109:
108:
105:
101:
100:
95:
91:
90:
81:
77:
76:
67:
63:
62:
57:
56:Classification
53:
52:
49:
41:
40:
25:Doomsday Clock
15:
9:
6:
4:
3:
2:
15103:
15092:
15089:
15087:
15084:
15082:
15079:
15077:
15074:
15072:
15071:Atomic clocks
15069:
15068:
15066:
15051:
15048:
15047:
15045:
15041:
15035:
15032:
15030:
15027:
15025:
15022:
15020:
15017:
15015:
15012:
15010:
15007:
15005:
15002:
15000:
14997:
14996:
14994:
14992:Miscellaneous
14990:
14984:
14981:
14980:
14978:
14976:
14972:
14966:
14963:
14961:
14958:
14956:
14953:
14951:
14948:
14946:
14943:
14941:
14938:
14937:
14935:
14933:
14929:
14923:
14920:
14918:
14915:
14913:
14910:
14908:
14905:
14903:
14900:
14899:
14897:
14895:
14891:
14885:
14882:
14880:
14877:
14875:
14874:Water turbine
14872:
14870:
14869:Steam turbine
14867:
14865:
14862:
14860:
14857:
14855:
14852:
14851:
14849:
14847:
14843:
14837:
14834:
14832:
14829:
14828:
14826:
14824:
14820:
14814:
14811:
14809:
14808:Rotary engine
14806:
14804:
14801:
14799:
14796:
14795:
14793:
14791:
14787:
14781:
14778:
14776:
14773:
14772:
14770:
14768:
14764:
14758:
14755:
14753:
14750:
14748:
14745:
14743:
14742:Hydraulic ram
14740:
14738:
14735:
14733:
14730:
14729:
14727:
14725:
14721:
14717:
14711:
14708:
14706:
14703:
14701:
14698:
14696:
14693:
14692:
14690:
14688:
14684:
14678:
14675:
14673:
14670:
14668:
14665:
14663:
14660:
14658:
14655:
14653:
14650:
14649:
14647:
14645:
14641:
14637:
14630:
14625:
14623:
14618:
14616:
14611:
14610:
14607:
14595:
14592:
14590:
14587:
14585:
14582:
14580:
14577:
14575:
14572:
14570:
14567:
14565:
14562:
14558:
14555:
14554:
14553:
14550:
14548:
14545:
14544:
14542:
14538:
14532:
14529:
14527:
14524:
14522:
14519:
14517:
14514:
14512:
14509:
14507:
14504:
14502:
14499:
14497:
14494:
14492:
14489:
14487:
14484:
14482:
14479:
14477:
14474:
14472:
14469:
14467:
14464:
14462:
14459:
14457:
14454:
14452:
14449:
14447:
14444:
14442:
14439:
14438:
14436:
14434:
14433:units of time
14429:
14423:
14422:Sidereal time
14420:
14418:
14415:
14413:
14410:
14408:
14407:Galactic year
14405:
14404:
14402:
14400:
14396:
14390:
14387:
14385:
14382:
14380:
14377:
14376:
14374:
14370:
14364:
14363:Weekday names
14361:
14359:
14356:
14354:
14353:Tropical year
14351:
14349:
14346:
14344:
14341:
14339:
14336:
14334:
14331:
14329:
14326:
14324:
14321:
14319:
14318:Intercalation
14316:
14314:
14311:
14309:
14306:
14304:
14301:
14299:
14296:
14294:
14291:
14289:
14286:
14284:(lunar Hijri)
14283:
14280:
14278:
14275:
14273:
14270:
14268:
14265:
14263:
14260:
14259:
14257:
14255:
14251:
14245:
14242:
14240:
14237:
14235:
14232:
14230:
14227:
14225:
14222:
14220:
14217:
14213:
14210:
14209:
14208:
14205:
14203:
14200:
14198:
14195:
14193:
14190:
14188:
14185:
14183:
14180:
14178:
14175:
14173:
14170:
14168:
14165:
14163:
14160:
14159:
14157:
14155:
14151:
14145:
14142:
14140:
14137:
14135:
14132:
14130:
14127:
14125:
14124:Time dilation
14122:
14120:
14117:
14115:
14112:
14110:
14107:
14105:
14102:
14100:
14097:
14095:
14092:
14090:
14087:
14085:
14082:
14080:
14077:
14076:
14074:
14072:
14068:
14062:
14059:
14057:
14054:
14052:
14049:
14048:
14046:
14042:
14037:
14031:
14021:
14018:
14016:
14013:
14011:
14008:
14006:
14003:
14001:
13998:
13996:
13993:
13991:
13988:
13986:
13983:
13981:
13978:
13976:
13973:
13971:
13968:
13966:
13963:
13961:
13960:24-hour clock
13958:
13956:
13955:12-hour clock
13953:
13951:
13948:
13946:
13943:
13941:
13938:
13936:
13933:
13931:
13928:
13926:
13923:
13921:
13918:
13914:
13911:
13910:
13909:
13906:
13905:
13903:
13899:
13893:
13890:
13888:
13885:
13883:
13880:
13879:
13876:
13872:
13868:
13861:
13856:
13854:
13849:
13847:
13842:
13841:
13838:
13826:
13823:
13821:
13818:
13816:
13813:
13812:
13810:
13806:
13800:
13797:
13795:
13792:
13790:
13787:
13786:
13784:
13780:
13776:
13769:
13764:
13762:
13757:
13755:
13750:
13749:
13746:
13734:
13726:
13724:
13716:
13715:
13712:
13706:
13703:
13701:
13698:
13696:
13693:
13691:
13690:
13686:
13684:
13681:
13679:
13676:
13674:
13671:
13669:
13666:
13664:
13661:
13660:
13658:
13654:
13644:
13641:
13639:
13636:
13634:
13631:
13627:
13624:
13623:
13622:
13621:Chronobiology
13619:
13617:
13614:
13613:
13611:
13607:
13601:
13598:
13596:
13593:
13591:
13588:
13586:
13583:
13581:
13578:
13576:
13573:
13571:
13568:
13566:
13563:
13561:
13558:
13556:
13555:Arrow of time
13553:
13551:
13548:
13547:
13545:
13543:
13539:
13533:
13530:
13528:
13527:Geochronology
13525:
13521:
13518:
13516:
13513:
13511:
13508:
13506:
13503:
13501:
13498:
13496:
13493:
13492:
13491:
13488:
13487:
13485:
13483:
13479:
13476:
13474:
13469:
13463:
13459:
13455:
13452:
13450:
13447:
13445:
13442:
13440:
13437:
13433:
13430:
13428:
13425:
13424:
13423:
13420:
13418:
13415:
13413:
13410:
13408:
13405:
13404:
13402:
13400:
13395:
13391:
13383:
13380:
13379:
13378:
13377:Wheel of time
13375:
13371:
13368:
13367:
13366:
13363:
13361:
13358:
13356:
13353:
13351:
13348:
13346:
13343:
13341:
13338:
13337:
13335:
13330:
13327:
13325:
13322:
13321:
13318:
13312:
13311:
13307:
13305:
13302:
13300:
13297:
13295:
13292:
13290:
13287:
13285:
13282:
13280:
13277:
13275:
13272:
13270:
13267:
13265:
13262:
13260:
13257:
13255:
13252:
13250:
13247:
13246:
13244:
13242:
13238:
13232:
13229:
13227:
13224:
13222:
13221:Periodization
13219:
13217:
13214:
13212:
13209:
13207:
13204:
13202:
13199:
13198:
13196:
13191:
13188:
13186:
13183:
13182:
13179:
13167:
13166:
13162:
13161:
13160:
13159:
13155:
13153:
13150:
13148:
13147:Digital clock
13145:
13143:
13140:
13136:
13133:
13129:
13126:
13124:
13121:
13120:
13119:
13116:
13114:
13111:
13109:
13106:
13104:
13101:
13097:
13094:
13093:
13092:
13089:
13085:
13082:
13081:
13080:
13077:
13076:
13075:
13072:
13071:
13069:
13067:
13063:
13057:
13056:
13052:
13050:
13047:
13045:
13042:
13040:
13037:
13035:
13032:
13030:
13027:
13025:
13022:
13020:
13017:
13015:
13012:
13008:
13005:
13003:
13000:
12998:
12995:
12994:
12993:
12990:
12989:
12987:
12985:
12981:
12975:
12972:
12970:
12967:
12965:
12962:
12960:
12957:
12955:
12952:
12950:
12947:
12945:
12942:
12940:
12937:
12935:
12932:
12930:
12927:
12925:
12924:Relative hour
12922:
12920:
12919:24-hour clock
12917:
12915:
12914:12-hour clock
12912:
12910:
12907:
12905:
12902:
12901:
12899:
12897:
12891:
12885:
12882:
12880:
12877:
12875:
12872:
12870:
12867:
12865:
12862:
12861:
12859:
12857:
12853:
12850:
12848:
12843:
12839:
12833:
12830:
12828:
12825:
12823:
12820:
12818:
12815:
12814:
12812:
12808:
12804:
12797:
12792:
12790:
12785:
12783:
12778:
12777:
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12763:
12757:
12753:
12752:
12744:
12729:
12725:
12719:
12704:
12700:
12696:
12691:
12675:
12671:
12665:
12650:
12646:
12642:
12637:
12629:
12625:
12621:
12617:
12613:
12609:
12605:
12601:
12596:
12591:
12587:
12583:
12575:
12560:
12556:
12552:
12548:
12541:
12526:
12522:
12515:
12508:
12504:
12501:
12495:
12493:
12476:
12472:
12466:
12450:
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12440:
12425:
12421:
12414:
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12392:
12377:
12373:
12366:
12350:
12346:
12345:
12340:
12333:
12317:
12313:
12309:
12303:
12287:
12283:
12279:
12272:
12256:
12252:
12246:
12230:
12226:
12220:
12201:
12194:
12188:
12182:
12177:
12162:
12158:
12154:
12150:
12143:
12127:
12123:
12119:
12113:
12094:
12087:
12081:
12065:
12061:
12057:
12051:
12035:
12031:
12027:
12021:
12005:
12001:
11995:
11976:
11969:
11963:
11947:
11943:
11937:
11921:
11917:
11911:
11892:
11885:
11879:
11860:
11853:
11847:
11831:
11827:
11821:
11819:
11802:
11798:
11792:
11773:
11766:
11760:
11744:
11740:
11739:navipedia.net
11736:
11730:
11714:
11710:
11704:
11688:
11684:
11678:
11672:Section 1.2.2
11658:
11651:
11645:
11629:
11625:
11621:
11615:
11599:
11595:
11589:
11570:
11566:
11559:
11552:
11541:
11537:
11530:
11523:
11507:
11503:
11497:
11489:
11483:
11479:
11475:
11469:
11454:
11450:
11446:
11441:
11433:
11429:
11424:
11419:
11415:
11411:
11407:
11403:
11399:
11395:
11391:
11384:
11376:
11370:
11362:
11358:
11354:
11350:
11346:
11342:
11338:
11334:
11330:
11326:
11319:
11317:
11308:
11304:
11300:
11296:
11292:
11288:
11284:
11280:
11276:
11272:
11265:
11257:
11253:
11249:
11245:
11241:
11237:
11233:
11229:
11224:
11219:
11216:(7): 073601.
11215:
11211:
11207:
11192:
11176:
11172:
11166:
11158:
11154:
11149:
11144:
11140:
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11132:
11128:
11123:
11118:
11114:
11110:
11106:
11098:
11082:
11076:
11068:
11064:
11060:
11056:
11052:
11048:
11043:
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11034:
11030:
11023:
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10995:
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10981:
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10929:
10923:
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10696:
10688:
10684:
10680:
10676:
10672:
10668:
10664:
10660:
10655:
10650:
10646:
10642:
10638:
10627:
10619:
10615:
10611:
10607:
10603:
10599:
10595:
10591:
10590:GPS Solutions
10584:
10576:
10560:
10556:
10552:
10548:
10544:
10540:
10536:
10532:
10528:
10523:
10518:
10514:
10510:
10506:
10498:
10482:
10478:
10474:
10467:
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10444:
10440:
10436:
10432:
10428:
10424:
10420:
10416:
10411:
10406:
10402:
10398:
10397:
10389:
10382:
10366:
10362:
10358:
10351:
10335:
10331:
10325:
10309:
10305:
10304:
10299:
10292:
10273:
10269:
10265:
10261:
10257:
10253:
10249:
10245:
10241:
10236:
10231:
10227:
10223:
10222:
10214:
10207:
10199:
10195:
10191:
10187:
10183:
10179:
10175:
10171:
10166:
10161:
10157:
10153:
10138:
10122:
10118:
10114:
10107:
10091:
10087:
10083:
10076:
10060:
10056:
10049:
10041:
10037:
10032:
10027:
10023:
10019:
10015:
10011:
10006:
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9997:
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9931:
9927:
9923:
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9913:
9909:
9905:
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9875:
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9865:
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9772:
9768:
9764:
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9741:
9737:
9731:
9715:
9711:
9705:
9690:
9686:
9682:
9678:
9671:
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9651:
9645:
9629:
9625:
9619:
9600:
9593:
9587:
9579:
9575:
9571:
9567:
9563:
9559:
9554:
9549:
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9541:
9537:
9533:
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9513:
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9486:
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9468:
9466:
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9435:
9428:
9417:
9413:
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9401:
9397:
9393:
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9376:
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9350:
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9340:
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9332:
9328:
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9317:
9309:
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9301:
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9289:
9285:
9281:
9276:
9271:
9267:
9263:
9259:
9252:
9250:
9233:
9229:
9223:
9215:
9211:
9207:
9203:
9199:
9195:
9191:
9187:
9184:(6501): 367.
9183:
9179:
9175:
9168:
9152:
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9142:
9126:
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9101:
9097:
9093:
9088:
9072:
9068:
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9034:
9029:
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8949:
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8896:
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8879:
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8855:
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8834:
8830:
8823:
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8499:in Th:LiSrAlF
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8350:
8347:(18) 182501.
8346:
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8049:
8045:transition".
8040:
8032:
8028:
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8020:
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7991:(12) 120802.
7990:
7986:
7979:
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7949:
7945:
7941:
7937:
7933:
7929:
7925:
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7540:New Scientist
7537:
7530:
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6187:
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6180:(12) 124705.
6179:
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6118:92-822-2213-6
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6087:
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6062:
6056:
6041:
6040:TNW | Science
6037:
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5420:
5416:
5412:
5408:
5404:
5400:
5395:
5390:
5386:
5382:
5378:
5367:
5352:
5348:
5344:
5339:
5331:
5327:
5322:
5317:
5313:
5309:
5305:
5301:
5297:
5293:
5288:
5283:
5279:
5275:
5271:
5256:
5241:
5237:
5230:
5215:
5211:
5204:
5185:
5181:
5177:
5173:
5169:
5165:
5161:
5160:
5152:
5145:
5137:
5133:
5129:
5125:
5121:
5117:
5113:
5109:
5104:
5099:
5095:
5091:
5087:
5080:
5065:
5061:
5054:
5046:
5040:
5036:
5032:
5026:
5010:
5006:
4999:
4991:
4987:
4983:
4979:
4975:
4971:
4968:(12): 23–30.
4967:
4963:
4962:Physics Today
4959:
4952:
4938:
4932:
4928:
4924:
4920:
4916:
4914:
4911:
4907:
4899:
4891:
4887:
4882:
4877:
4873:
4869:
4865:
4861:
4857:
4853:
4849:
4842:
4826:
4822:
4818:
4812:
4803:
4799:
4795:
4791:
4787:
4783:
4780:(4476): 280.
4779:
4775:
4771:
4765:
4749:
4745:
4741:
4735:
4727:
4723:
4719:
4715:
4711:
4707:
4703:
4699:
4695:
4689:
4670:
4666:
4662:
4655:
4648:
4629:
4625:
4621:
4620:
4612:
4605:
4603:
4601:
4599:
4597:
4588:
4584:
4579:
4574:
4570:
4566:
4562:
4558:
4554:
4547:
4539:
4535:
4531:
4527:
4523:
4519:
4515:
4511:
4507:
4500:
4484:
4480:
4474:
4460:
4458:9780444508713
4454:
4450:
4446:
4442:
4438:
4431:
4429:
4427:
4418:
4414:
4410:
4406:
4402:
4398:
4394:
4390:
4386:
4379:
4371:
4365:
4358:
4334:
4330:
4326:
4322:
4321:
4313:
4306:
4304:
4295:
4291:
4285:
4269:
4265:
4258:
4242:
4238:
4232:
4228:
4204:
4197:
4191:
4187:
4176:
4175:Optical clock
4173:
4171:
4170:Time transfer
4168:
4166:
4163:
4161:
4158:
4156:
4153:
4151:
4148:
4146:
4143:
4141:
4138:
4136:
4133:
4131:
4128:
4126:
4123:
4122:
4117:
4111:
4106:
4099:
4097:
4093:
4083:
4081:
4069:
4065:
4060:
4057:
4053:
4044:
4042:
4038:
4034:
4030:
4024:
4014:
4008:
3998:
3996:
3986:
3983:
3979:
3975:
3970:
3966:
3964:
3958:
3956:
3952:
3948:
3945:
3936:
3932:
3929:
3925:
3920:
3918:
3912:
3910:
3905:
3901:
3891:
3889:
3885:
3880:
3876:
3872:
3862:
3860:
3850:
3848:
3843:
3841:
3836:121.5 nm
3831:
3813:
3809:
3804:
3801:
3792:
3785:
3782:
3777:
3773:
3749:
3746:
3739:
3735:
3731:
3726:
3722:
3715:
3709:
3704:
3700:
3694:
3689:
3685:
3681:
3674:
3670:
3664:
3660:
3653:
3644:
3635:
3625:
3615:
3595:
3579:
3560:
3555:
3552:
3549:
3545:
3541:
3536:
3533:
3530:
3526:
3521:
3515:
3509:
3501:
3497:
3481:
3458:
3454:
3450:
3446:
3439:
3435:
3426:
3423:
3414:
3403:
3392:
3383:
3381:
3377:
3373:
3368:
3366:
3362:
3357:
3353:
3341:
3330:
3327:
3292:
3288:
3286:
3282:
3278:
3266:
3261:
3241:10 years
3234:
3230:
3218:
3217:ytterbium-171
3213:
3211:
3199:
3186:
3184:
3175:
3170:
3166:
3164:
3160:
3156:
3152:
3148:
3144:
3140:
3136:
3132:
3127:
3125:
3121:
3113:
3110:
3107:
3106:
3105:
3102:
3100:
3096:
3092:
3087:
3084:
3080:
3076:
3072:
3068:
3065:
3060:
3058:
3054:
3050:
3046:
3041:
3033:
3028:
3019:
3009:
3005:
3000:
2990:
2986:
2972:
2969:
2965:
2961:
2955:
2949:
2936:
2931:
2927:
2924:
2923:
2922:
2919:
2917:
2891:
2869:
2846:
2780:
2779:nuclear clock
2776:
2771:
2752:
2748:
2744:
2738:
2737:Nuclear clock
2728:
2726:
2725:ytterbium-171
2722:
2718:
2713:
2702:
2692:
2687:
2683:
2679:
2675:
2671:
2665:
2664:Quantum clock
2655:
2647:
2642:
2621:
2618:
2614:
2613:
2610:
2605:
2584:
2581:
2577:
2576:
2573:
2568:
2544:
2541:
2537:
2536:
2533:
2528:
2507:
2504:
2500:
2499:
2496:
2491:
2473:
2471:
2468:
2467:
2464:
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2438:
2436:
2433:
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2422:
2406:
2404:
2401:
2400:
2396:
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2343:
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2327:
2325:
2321:
2317:
2313:
2309:
2300:
2297:
2293:
2289:
2285:
2268:
2266:
2265:Dave Wineland
2262:
2258:
2245:
2237:
2232:
2223:
2206:
2178:
2175:
2171:
2149:
2144:
2138:
2134:
2110:
2104:
2099:
2095:
2088:
2084:
2078:
2075:
2067:
2064:
2058:
2055:
2049:
2045:
2036:
2030:
2027:
2024:
2008:
2004:
1998:
1992:
1967:
1964:
1960:
1952:
1951:
1950:
1948:
1932:
1929:
1926:
1923:
1920:
1898:
1894:
1889:
1883:
1879:
1875:
1872:
1850:
1846:
1825:
1802:
1784:
1780:
1771:
1767:
1763:
1757:
1741:
1737:
1716:
1708:
1690:
1668:
1645:
1619:
1598:
1590:
1589:spectroscopic
1574:
1548:
1542:
1533:
1521:
1514:
1510:
1504:
1495:
1489:
1461:
1458:
1454:
1446:
1445:
1444:
1427:
1419:
1415:
1407:
1402:
1400:
1394:
1390:
1373:
1362:
1344:
1340:
1330:
1324:
1321:
1317:
1316:crystal watch
1314:
1311:changes in a
1310:
1306:
1302:
1298:
1294:
1284:
1282:
1278:
1272:
1270:
1266:
1261:
1259:
1255:
1252:
1248:
1242:
1240:
1239:
1234:
1230:
1226:
1222:
1212:
1210:
1206:
1202:
1197:
1195:
1194:absolute zero
1191:
1171:
1156:
1154:
1150:
1146:
1140:
1138:
1134:
1128:
1120:
1115:
1105:
1103:
1099:
1086:
1078:
1073:
1063:
1061:
1056:
1046:
1042:
1038:
1034:
1025:
1019:Block diagram
1016:
1013:
1009:
1005:
1000:
998:
994:
990:
986:
981:
966:
964:
958:
957:0.9 seconds.
954:
952:
948:
944:
938:
932:
927:
919:
910:
908:
904:
899:
896:
890:
888:
884:
880:
876:
872:
861:
859:
856:
852:
840:
830:
814:
810:
806:
801:
799:
796:to provide a
795:
791:
786:
780:
776:
772:
768:
764:
760:
756:
752:
748:
744:
740:
736:
732:
727:
725:
721:
706:
704:
703:optical combs
700:
696:
692:
689:
687:
683:
678:
672:
668:
659:
650:
619:
606:precision of
605:
601:
597:
593:
589:
585:
576:
573:
569:
561:
557:
552:
543:
542:around 2030.
541:
537:
533:
529:
525:
521:
517:
513:
512:tropical year
479:
477:
473:
469:
464:
462:
458:
454:
450:
446:
442:
438:
434:
430:
426:
422:
417:
415:
410:
408:
404:
400:
396:
392:
383:
379:
377:
373:
369:
365:
361:
360:quartz clocks
357:
352:
350:
346:
341:
339:
335:
330:
326:
318:
314:
310:
301:
295:
291:
287:
283:
282:absolute zero
279:
275:
270:
266:1,000,000,000
258:
254:
250:
246:
242:
238:
234:
229:
227:
223:
219:
215:
209:
176:
162:
160:
156:
152:
148:
144:
143:energy levels
140:
136:
128:
124:
120:
115:
106:
102:
99:
96:
92:
89:
85:
82:
78:
75:
71:
68:
64:
61:
58:
54:
47:
42:
37:
34:
30:
26:
22:
15009:Agricultural
14864:Quasiturbine
14775:Steam engine
14710:Quartz clock
14695:Atomic clock
14694:
14569:Decimal time
14298:Astronomical
14177:Complication
14172:Atomic clock
14171:
13820:Atomic clock
13819:
13815:Quartz clock
13695:Time capsule
13689:Tempus fugit
13687:
13609:Other fields
13308:
13289:Perdurantism
13211:Calendar era
13163:
13156:
13142:Cuckoo clock
13090:
13079:astronomical
13053:
12879:Unit of time
12810:Key concepts
12750:
12743:
12731:. Retrieved
12727:
12718:
12706:. Retrieved
12702:
12690:
12678:. Retrieved
12673:
12664:
12652:. Retrieved
12648:
12636:
12585:
12581:
12574:
12562:. Retrieved
12550:
12540:
12528:. Retrieved
12524:
12514:
12479:. Retrieved
12474:
12465:
12453:. Retrieved
12448:
12439:
12427:. Retrieved
12423:
12413:
12401:. Retrieved
12391:
12379:. Retrieved
12375:
12365:
12353:. Retrieved
12342:
12332:
12320:. Retrieved
12316:the original
12311:
12302:
12290:. Retrieved
12282:livemint.com
12281:
12271:
12259:. Retrieved
12245:
12233:. Retrieved
12219:
12207:. Retrieved
12187:
12176:
12164:. Retrieved
12152:
12142:
12130:. Retrieved
12126:the original
12121:
12112:
12100:. Retrieved
12080:
12068:. Retrieved
12059:
12050:
12038:. Retrieved
12029:
12020:
12008:. Retrieved
12004:the original
11994:
11982:. Retrieved
11962:
11950:. Retrieved
11936:
11924:. Retrieved
11910:
11898:. Retrieved
11878:
11866:. Retrieved
11859:the original
11846:
11834:. Retrieved
11805:. Retrieved
11791:
11779:. Retrieved
11759:
11747:. Retrieved
11738:
11729:
11717:. Retrieved
11713:the original
11703:
11691:. Retrieved
11687:the original
11677:
11664:. Retrieved
11644:
11632:. Retrieved
11623:
11614:
11602:. Retrieved
11588:
11576:. Retrieved
11564:
11551:
11535:
11522:
11510:. Retrieved
11506:the original
11496:
11477:
11468:
11456:. Retrieved
11452:
11440:
11397:
11393:
11383:
11369:
11328:
11324:
11274:
11270:
11264:
11213:
11209:
11206:Uncertainty"
11191:
11179:. Retrieved
11174:
11165:
11112:
11108:
11097:
11085:. Retrieved
11075:
11032:
11028:
11022:
10979:
10975:
10968:
10938:(2): 82–83.
10935:
10931:
10922:
10910:. Retrieved
10896:
10853:
10849:
10843:
10831:. Retrieved
10817:
10766:
10762:
10752:
10709:
10705:
10695:
10647:(3) 033201.
10644:
10640:
10626:
10593:
10589:
10575:
10563:. Retrieved
10512:
10508:
10497:
10485:. Retrieved
10476:
10466:
10454:. Retrieved
10400:
10394:
10381:
10369:. Retrieved
10360:
10350:
10338:. Retrieved
10324:
10312:. Retrieved
10301:
10291:
10279:. Retrieved
10272:the original
10225:
10219:
10206:
10158:(6) 063001.
10155:
10151:
10137:
10125:. Retrieved
10116:
10106:
10094:. Retrieved
10085:
10075:
10063:. Retrieved
10059:the original
10055:"About Time"
10048:
9995:
9991:
9973:
9961:. Retrieved
9907:
9903:
9890:
9878:. Retrieved
9864:
9852:. Retrieved
9843:
9834:
9822:. Retrieved
9797:
9787:
9775:. Retrieved
9766:
9756:
9744:. Retrieved
9739:
9730:
9718:. Retrieved
9704:
9692:. Retrieved
9680:
9670:
9658:. Retrieved
9644:
9632:. Retrieved
9618:
9606:. Retrieved
9586:
9535:
9531:
9521:
9500:
9488:. Retrieved
9476:
9452:. Retrieved
9445:the original
9440:
9427:
9416:the original
9390:(2) 020801.
9387:
9381:
9326:
9316:
9265:
9261:
9238:21 September
9236:. Retrieved
9231:
9222:
9181:
9177:
9167:
9155:. Retrieved
9150:
9141:
9129:. Retrieved
9124:
9115:
9103:. Retrieved
9099:
9087:
9075:. Retrieved
9056:
9044:. Retrieved
9040:
9028:
8979:
8975:
8964:
8952:. Retrieved
8938:
8885:
8881:
8871:
8836:
8832:
8822:
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8783:
8773:
8761:. Retrieved
8745:
8738:
8722:
8679:(4) 042501.
8676:
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8630:(2) kHz
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8420:(1) 013201.
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8372:
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8172:
8165:
8114:
8110:
8103:
8052:
8046:
8039:
7988:
7984:
7965:11 September
7963:. Retrieved
7956:the original
7927:
7923:
7910:
7859:
7855:
7845:
7826:
7822:
7809:
7790:
7786:
7776:
7764:. Retrieved
7749:
7701:(3) 033201.
7698:
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7688:
7676:. Retrieved
7625:(7) 070802.
7622:
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7586:
7574:. Retrieved
7565:
7555:
7543:. Retrieved
7539:
7529:
7517:. Retrieved
7512:
7503:
7491:. Retrieved
7487:
7477:
7465:. Retrieved
7460:
7451:
7408:
7404:
7394:
7382:. Retrieved
7368:
7320:(6) 063001.
7317:
7313:
7303:
7291:. Retrieved
7277:
7229:(3) 033201.
7226:
7222:
7212:
7200:. Retrieved
7186:
7174:. Retrieved
7154:
7144:26 September
7142:. Retrieved
7099:(5) 052503.
7096:
7092:
7079:
7046:
7042:
7033:
7021:. Retrieved
7001:
6989:. Retrieved
6976:
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6938:
6926:. Retrieved
6914:
6901:
6864:
6860:
6850:
6828:
6816:. Retrieved
6807:
6797:
6785:. Retrieved
6776:
6767:
6755:. Retrieved
6751:
6739:
6727:. Retrieved
6715:
6710:Mann, Adam.
6705:
6693:. Retrieved
6688:
6679:
6667:. Retrieved
6663:
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6642:. Retrieved
6638:
6628:
6616:. Retrieved
6611:
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6154:
6141:
6130:, retrieved
6104:
6094:
6079:
6067:. Retrieved
6055:
6043:. Retrieved
6039:
6029:
6017:. Retrieved
6014:SciTechDaily
6013:
6003:
5991:. Retrieved
5982:
5973:
5961:. Retrieved
5957:
5948:
5936:. Retrieved
5932:
5922:
5910:. Retrieved
5906:
5896:
5884:. Retrieved
5850:
5844:
5833:, retrieved
5813:
5807:
5798:
5769:. Retrieved
5765:
5756:
5744:. Retrieved
5740:
5728:
5716:. Retrieved
5712:
5700:
5688:. Retrieved
5684:
5672:
5663:
5657:
5633:. Retrieved
5629:the original
5600:. Retrieved
5593:the original
5548:
5544:
5534:
5522:. Retrieved
5518:Science News
5517:
5508:
5449:
5445:
5435:
5387:(3) 033201.
5384:
5380:
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5350:
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5239:
5229:
5217:. Retrieved
5213:
5203:
5191:. Retrieved
5163:
5157:
5144:
5096:(5) 055009.
5093:
5089:
5079:
5067:. Retrieved
5063:
5053:
5034:
5025:
5013:. Retrieved
5009:the original
4998:
4965:
4961:
4951:
4940:, retrieved
4918:
4912:
4909:
4905:
4898:
4855:
4851:
4841:
4829:. Retrieved
4820:
4811:
4777:
4773:
4764:
4752:. Retrieved
4743:
4734:
4701:
4697:
4688:
4676:. Retrieved
4660:
4647:
4635:. Retrieved
4626:(4): 74–89.
4623:
4617:
4560:
4556:
4546:
4513:
4509:
4499:
4487:. Retrieved
4482:
4473:
4462:, retrieved
4440:
4395:(3): S1–S3.
4392:
4388:
4378:
4364:cite journal
4336:
4324:
4318:
4293:
4284:
4272:. Retrieved
4267:
4257:
4245:. Retrieved
4231:
4203:
4190:
4155:Pulsar clock
4089:
4061:
4050:
4026:
4004:
3992:
3982:Asia-Pacific
3971:
3967:
3959:
3941:
3921:
3917:leap seconds
3913:
3897:
3868:
3865:Applications
3859:fiber-optics
3856:
3853:Requirements
3844:
3832:
3631:
3580:
3499:
3495:
3415:
3398:
3389:
3369:
3358:
3354:
3342:
3298:
3262:
3243:); this was
3214:
3198:strontium-87
3187:
3179:
3128:
3117:
3103:
3088:
3061:
3045:John L. Hall
3037:
3001:
2973:
2956:
2945:
2920:
2847:
2742:
2740:
2721:strontium-87
2714:
2703:
2667:
2652:
2368:
2352:
2328:
2310:'s NPL-CsF2
2301:
2269:
2240:
2125:
1758:
1563:
1403:
1395:
1388:
1328:
1325:
1290:
1280:
1276:
1273:
1262:
1243:
1236:
1218:
1209:derived unit
1198:
1186: cycles
1173:
1141:
1129:
1125:
1087:
1085:the second.
1083:
1057:
1030:
1001:
987:
983:
959:
955:
939:
928:
924:
900:
891:
867:
853:
841:
802:
787:
728:
724:energy state
717:
695:Metrologists
693:
690:
664:
620:
577:
565:
485:
465:
444:
418:
411:
395:Jean Brossel
388:
353:
342:
322:
278:temperatures
271:
235:such as the
230:
222:leap seconds
211:
164:
135:atomic clock
134:
132:
39:Atomic clock
33:
15024:Wind tunnel
14940:Vacuum tube
14932:Electronics
14854:Gas turbine
14798:Gas turbine
14757:Vacuum pump
14720:Compressors
14700:Chronometer
14579:System time
14574:Metric time
14293:Solar Hijri
14219:Water clock
14202:Radio clock
14134:Time domain
14114:Proper time
14000:Leap second
13882:Chronometry
13825:Radio clock
13705:Time travel
13683:System time
13590:Time domain
13575:Proper time
13399:use of time
13370:Father Time
13350:Immortality
13340:Ages of Man
13269:Endurantism
13226:Regnal year
13206:Big History
13135:water-based
13034:Solar Hijri
12944:Hexadecimal
12894:Measurement
12856:Chronometry
12842:Measurement
12733:16 February
12708:16 February
12680:16 February
12654:17 February
12564:15 February
12530:16 February
12481:15 February
12455:15 February
12429:20 February
12403:20 February
12381:20 February
12292:27 December
12261:27 December
12166:15 February
11836:30 December
11807:15 December
11596:. Galleon.
11458:15 February
11181:23 November
11087:20 February
10833:29 December
10565:16 February
9963:5 September
9746:11 February
9694:15 February
9490:11 February
9157:16 February
9131:11 February
9105:14 February
9046:16 February
8954:13 November
8655:ScienceNews
7829:(11) 2194.
7766:4 September
7545:11 February
7519:11 February
7493:11 February
7467:11 February
7457:"StackPath"
6977:SI Brochure
6928:11 February
6757:20 February
6729:15 February
6695:20 February
6669:20 February
6664:EurekAlert!
6644:20 February
6132:16 December
6069:24 February
6045:16 February
6019:16 February
5963:19 February
5938:19 February
5912:19 February
5771:17 February
5746:11 February
5524:22 February
5356:21 February
5245:21 February
5219:16 February
5193:25 February
5069:16 February
5058:Fox, Alex.
5015:16 February
4831:20 November
4247:23 November
4135:Dick effect
4130:Clock drift
4029:radio clock
4023:Radio clock
3909:nanoseconds
3879:time signal
3194: atoms
3099:phase noise
3077:instead of
3064:femtosecond
2619:, 688 THz)
2582:, 642 THz)
1762:Dick effect
1320:temperature
1258:demodulated
895:nanoseconds
798:proper time
376:Louis Essen
364:Lord Kelvin
329:light waves
313:Louis Essen
294:uncertainty
98:Electricity
94:Fuel source
80:Application
21:Radio clock
15065:Categories
14983:Automobile
14945:Transistor
14859:Jet engine
14831:Pantograph
14594:Timekeeper
14547:Chronology
14531:Millennium
14417:Precession
14323:Julian day
14144:T-symmetry
14005:Solar time
13975:Civil time
13808:Electronic
13407:Chronemics
13382:Kalachakra
13294:Presentism
13279:Eternalism
13185:Chronology
13123:mechanical
13074:Main types
12992:Main types
12595:2109.12238
12070:30 January
12040:30 January
11952:1 February
11926:16 January
11604:12 October
11223:1609.06183
11122:2308.12457
11035:(2): 673.
10989:1511.03888
10776:2109.12237
10719:1807.11282
10654:1902.07694
10522:2006.07501
10410:1711.08540
10235:1702.01210
10165:1602.03908
10096:17 October
9880:19 January
9777:5 December
9720:5 December
9660:3 November
9634:3 November
9512:2004.09987
9275:1909.05384
8895:1511.07735
8763:2 December
8686:1801.05205
8536:2406.18719
8427:2404.12311
8252:1905.06308
8188:1902.04823
8124:1709.05325
8062:1710.11398
7862:(1) 8022.
7708:1902.07694
7678:9 February
7418:1507.04754
7384:9 December
7327:1602.03908
7293:9 December
7236:1902.07694
7202:9 December
7043:Metrologia
6841:1709.03256
6818:18 October
6393:Allan, D.
5635:17 January
5558:2307.14141
5545:Metrologia
5459:2109.12238
5394:1902.07694
5280:(1) 6896.
5103:1911.05551
5090:Metrologia
4754:17 October
4637:24 October
4563:(4): 318.
4389:Metrologia
4320:Metrologia
4223:References
3583:10 Hz
3326:degenerate
3153:, Ca, Yb,
3079:microwaves
3030:May 2009–
2987:(879
2966:, both in
2843:10 Hz
2825:2 kHz
2775:gamma rays
2773:produces "
2397:Reference
1233:microwaves
1094:10 mm
829:calibrated
682:milliwatts
472:Atomichron
257:nanosecond
15086:Metrology
14960:Capacitor
14922:Propeller
14491:Fortnight
14338:Lunisolar
14328:Leap year
14262:Gregorian
14212:stopwatch
14187:Hourglass
14167:Astrarium
14084:Spacetime
14015:Time zone
13892:Metrology
13871:standards
13663:Leap year
13580:Spacetime
13454:Yesterday
13355:Dreamtime
13329:Mythology
13216:Deep time
13128:stopwatch
13103:hourglass
13084:astrarium
13014:Gregorian
13007:Lunisolar
12984:Calendars
12974:Time zone
12847:standards
12628:237940816
12559:1059-1028
12209:5 October
12161:0362-4331
12132:5 October
12102:5 October
11900:5 October
11868:3 October
11781:2 October
11749:2 October
11693:4 October
11666:4 October
11634:4 October
11414:2095-5138
11240:0031-9007
11067:119116973
11042:1407.3493
11014:119112716
10960:119938546
10888:118430700
10863:1401.2378
10809:237940240
10687:119075546
10671:0031-9007
10618:233030680
10596:(3): 83.
10555:229300882
10268:206656201
10117:The Verge
10005:1412.8261
9917:1309.1137
9854:24 August
9824:24 August
9814:124850552
9689:1059-1028
9578:239652525
9562:1094-4087
9485:1357-0978
9353:245520666
9308:202565677
9300:2399-3650
9268:(1) 153.
9206:0036-8075
9020:232355391
9004:1476-4687
8888:: 12443.
8729:1 μs
8473: GHz
8285:155090121
8221:119083861
8095:205248786
7998:1110.2490
7952:250818523
7884:2045-2322
7741:119075546
7632:0911.4527
7269:119075546
7071:250828528
6983:. 2014 .
6724:1059-1028
6551:0909.0909
6381:118430700
6356:1401.2378
6328:119116973
6303:1407.3493
6270:118430700
6245:1401.2378
6210:245079164
5873:1994-9405
5500:246902611
5484:0028-0836
5427:119075546
5411:0031-9007
5312:2041-1723
5287:1412.8261
5136:202129810
5128:0026-1394
4990:0031-9228
4872:0160-1741
4770:Essen, L.
4694:Essen, L.
4587:0031-899X
4538:0031-899X
4417:122631200
4409:0026-1394
4355:80 K
4059:scales.
4005:In 2022,
3797:∞
3786:−
3783:≈
3736:α
3686:ε
3649:∞
3593:Δ
3561:τ
3534:π
3516:τ
3510:σ
3482:σ
3433:Δ
3427:∝
3424:σ
3329:Fermi gas
3263:In 2015,
3095:bandwidth
3083:terahertz
2912:10 s
2719:based on
2691:magnesium
2682:aluminium
2678:beryllium
2389:Relative
2347:strontium
2292:ytterbium
2288:strontium
2278:and even
2207:τ
2172:σ
2150:τ
2105:τ
2089:⋅
2076:π
2065:π
2059:
2046:⋅
2031:
2005:σ
1999:≈
1993:τ
1961:σ
1826:τ
1803:τ
1781:σ
1738:ν
1717:τ
1669:ν
1666:Δ
1646:τ
1575:ν
1572:Δ
1543:τ
1511:ν
1505:ν
1502:Δ
1496:≈
1490:τ
1455:σ
1428:τ
1416:σ
1399:precision
1374:ν
1371:Δ
1361:resonance
1341:ν
1277:dead time
1251:modulated
1235:(the gas
1060:resonance
779:blackbody
731:metrology
720:microwave
699:ion traps
675:125
631:1 mm
604:frequency
596:strontium
584:ytterbium
556:ytterbium
455:, Bomac,
389:In 1949,
177:ν
173:Δ
147:frequency
127:Microsemi
14975:Vehicles
14965:Inductor
14955:Resistor
14894:Aerofoil
14884:Windmill
14823:Linkages
14636:Machines
14552:Duration
14526:Saeculum
14506:Olympiad
14348:Solstice
14277:Holocene
14254:Calendar
14154:Horology
13945:ISO 8601
13940:ISO 31-1
13723:Category
13471:Time in
13462:Tomorrow
13324:Religion
13264:Duration
13231:Timeline
13165:Timeline
12964:Sidereal
12832:Eternity
12620:35173346
12503:Archived
12355:29 April
12349:Archived
12286:Archived
12255:Archived
12229:Archived
12200:Archived
12093:Archived
12064:Archived
12034:Archived
11984:28 March
11975:Archived
11946:Archived
11920:Archived
11891:Archived
11830:Archived
11801:Archived
11772:Archived
11743:Archived
11657:Archived
11628:Archived
11598:Archived
11578:27 April
11569:Archived
11565:GPSworld
11540:Archived
11432:34691520
11353:21930568
11299:21930568
11256:40822816
11248:28256845
11157:38658684
11148:11043038
10906:Archived
10904:. BIPM.
10827:Archived
10825:. BIPM.
10801:35173344
10744:30487601
10679:31386450
10559:Archived
10547:33328668
10487:30 March
10481:Archived
10456:30 March
10447:Archived
10435:29570334
10371:30 March
10365:Archived
10340:29 March
10334:Archived
10314:29 March
10308:Archived
10303:Wired UK
10281:29 March
10260:28983047
10198:19870627
10190:26918984
10121:Archived
10090:Archived
10040:25898253
9954:Archived
9942:24463513
9874:Archived
9848:Archived
9818:Archived
9771:Archived
9714:Archived
9654:Archived
9628:Archived
9599:Archived
9570:34809077
9477:Wired UK
9412:16907426
9214:32675346
9071:Archived
9012:33762766
8948:Archived
8930:27503795
8863:26040875
8814:26040875
8754:Archived
8719:37518294
8711:28186791
8454: nm
8369:38759160
8277:31511684
8213:31511686
8149:29670266
8087:27147026
8031:40863227
8023:22540568
7902:29789631
7760:Archived
7733:31386450
7669:Archived
7665:13936087
7657:20366869
7594:Archived
7570:Archived
7488:phys.org
7443:20466105
7435:26863657
7378:Archived
7360:19870627
7352:26918984
7287:Archived
7261:31386450
7196:Archived
7167:Archived
7135:Archived
7039:Essen, L
7014:Archived
6985:Archived
6919:Archived
6893:34691520
6812:Archived
6781:Archived
6639:phys.org
6576:10581032
6568:20211780
6476:12303876
6468:18244242
6202:34972462
6123:archived
6102:(2006),
5987:Archived
5877:Archived
5826:archived
5647:Archived
5643:NIST.gov
5492:35173346
5419:31386450
5330:25898253
5184:Archived
4890:34566107
4825:Archived
4748:Archived
4669:Archived
4628:Archived
4274:30 April
4241:Archived
4102:See also
3963:rubidium
3875:Internet
3474:, where
3245:10 times
3006:(1
2929:orbital.
2355:accurate
2337:Research
2226:Accuracy
2163:as does
1297:pendulum
1151:such as
1127:second.
1108:Hydrogen
1066:Rubidium
1008:nitrogen
1004:hydrogen
945:and the
889:system.
855:Hydrogen
813:rubidium
751:Maryland
747:Colorado
592:aluminum
524:kilogram
249:accuracy
66:Industry
15043:Springs
14846:Turbine
14521:Century
14511:Lustrum
14441:Instant
14313:Equinox
14282:Islamic
14224:Sundial
14089:Chronon
13733:Commons
13656:Related
13570:Instant
13560:Chronon
13542:Physics
13482:Geology
13473:science
13345:Destiny
13190:History
13158:History
13113:sundial
13096:quantum
13039:Chinese
13029:Islamic
12939:Decimal
12934:Chinese
12896:systems
12822:Present
12600:Bibcode
12322:23 June
12312:Reuters
12235:22 June
12010:3 March
11512:26 June
11423:8288775
11361:6896025
11333:Bibcode
11307:6896025
11279:Bibcode
11127:Bibcode
11047:Bibcode
10994:Bibcode
10940:Bibcode
10912:25 June
10868:Bibcode
10781:Bibcode
10724:Bibcode
10598:Bibcode
10527:Bibcode
10443:3763878
10415:Bibcode
10240:Bibcode
10221:Science
10170:Bibcode
10127:26 June
10065:27 June
10031:4411304
10010:Bibcode
9950:4461081
9922:Bibcode
9608:26 June
9540:Bibcode
9454:22 June
9392:Bibcode
9280:Bibcode
9186:Bibcode
9178:Science
9077:10 July
8984:Bibcode
8921:4980484
8900:Bibcode
8841:Bibcode
8792:Bibcode
8691:Bibcode
8585:
8573:
8517:Ye, Jun
8485: s
8477:568(13)
8442:148.382
8349:Bibcode
8305:Physics
8257:Bibcode
8193:Bibcode
8157:4990345
8129:Bibcode
8067:Bibcode
8003:Bibcode
7932:Bibcode
7893:5964087
7864:Bibcode
7787:Physics
7713:Bibcode
7637:Bibcode
7576:27 July
7332:Bibcode
7241:Bibcode
7176:25 June
7131:3957861
7111:Bibcode
7051:Bibcode
7023:22 June
6991:23 June
6949:Science
6884:8288775
6787:3 April
6618:20 July
6505:Bibcode
6361:Bibcode
6308:Bibcode
6250:Bibcode
6182:Bibcode
5993:13 July
5886:16 June
5835:16 June
5718:21 June
5690:20 June
5602:12 June
5464:Bibcode
5321:4411304
5292:Bibcode
5168:Bibcode
5108:Bibcode
4970:Bibcode
4942:20 June
4881:6768155
4802:4191481
4782:Bibcode
4726:4191481
4706:Bibcode
4565:Bibcode
4518:Bibcode
4489:20 June
4464:20 June
3944:Galileo
3624:atoms.
3285:geodesy
3172:One of
3097:of the
2743:nuclear
2686:mercury
2316:NIST-F2
1587:is the
1359:of the
1309:voltage
1293:sundial
1047:(about
1033:caesium
1012:caesium
997:NIST-F2
993:NIST-F1
989:Caesium
974:Caesium
883:Galileo
757:in the
753:, USA,
588:mercury
560:photons
538:or the
368:ammonia
304:History
290:NIST-F2
274:caesium
264:⁄
104:Powered
74:science
15076:Clocks
14912:Rudder
14752:Trompe
14687:Clocks
14662:Pulley
14516:Decade
14471:Moment
14466:Minute
14461:Second
14431:Other
14288:Julian
14267:Hebrew
13913:offset
13673:Moment
13668:Memory
13520:period
13108:marine
13091:atomic
13066:Clocks
13024:Hebrew
13019:Julian
12954:Metric
12827:Future
12758:
12626:
12618:
12582:Nature
12557:
12159:
11719:2 July
11624:qps.nl
11484:
11430:
11420:
11412:
11359:
11351:
11305:
11297:
11254:
11246:
11238:
11155:
11145:
11109:Nature
11083:. BIPM
11065:
11012:
10976:Optica
10958:
10886:
10807:
10799:
10763:Nature
10742:
10706:Nature
10685:
10677:
10669:
10616:
10553:
10545:
10509:Nature
10441:
10433:
10266:
10258:
10196:
10188:
10038:
10028:
9948:
9940:
9904:Nature
9812:
9798:Nature
9687:
9576:
9568:
9560:
9483:
9410:
9351:
9341:
9306:
9298:
9212:
9204:
9018:
9010:
9002:
8976:Nature
8928:
8918:
8861:
8833:Nature
8812:
8784:Nature
8717:
8709:
8522:Nature
8367:
8283:
8275:
8238:Nature
8219:
8211:
8174:Nature
8155:
8147:
8111:Nature
8093:
8085:
8048:Nature
8029:
8021:
7950:
7900:
7890:
7882:
7739:
7731:
7663:
7655:
7441:
7433:
7358:
7350:
7267:
7259:
7129:
7069:
6891:
6881:
6722:
6574:
6566:
6474:
6466:
6379:
6349:(12).
6326:
6268:
6208:
6200:
6115:
6086:"OC18"
5871:
5861:
5498:
5490:
5482:
5446:Nature
5425:
5417:
5409:
5328:
5318:
5310:
5134:
5126:
5041:
4988:
4933:
4888:
4878:
4870:
4806:p.280.
4800:
4774:Nature
4724:
4698:Nature
4585:
4536:
4455:
4415:
4407:
3372:iodine
3281:Jun Ye
3257:578 nm
3215:Using
3141:, Sr,
3133:, Hg,
3120:Lasers
3093:, the
3040:lasers
1945:, the
1772:where
1564:where
1313:quartz
1254:signal
1170:Second
887:BeiDou
858:masers
761:, the
743:(NIST)
737:, the
594:, and
568:lasers
526:, and
520:kelvin
516:ampere
457:Varian
451:, the
441:French
159:second
15004:Robot
14999:Mecha
14950:Diode
14724:pumps
14672:Wedge
14667:Screw
14657:Lever
14557:music
14496:Month
14456:Jiffy
14451:Shake
14446:Flick
14343:Solar
14333:Lunar
14308:Epact
14272:Hindu
14207:Watch
14162:Clock
13678:Space
13510:epoch
13500:chron
13458:Today
13427:tempo
13422:Music
13284:Event
13118:watch
13002:Lunar
12997:Solar
12969:Solar
12959:Roman
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