84:
92:
493:, which has a superconducting critical temperature in bulk form of 9.3 K. Niobium, however, does not form an oxide that is suitable for making tunnel junctions. To form an insulating oxide, the first layer of niobium can be coated with a very thin layer (approximately 5 nm) of aluminum, which is then oxidized to form a high quality aluminum oxide tunnel barrier before the final layer of niobium is deposited. The thin aluminum layer is
120:
694:
When a high frequency current is applied to a
Josephson junction, the ac Josephson current will synchronize with the applied frequency giving rise to regions of constant voltage in the I–V curve of the device (Shapiro steps). For the purpose of voltage standards, these steps occur at the voltages
586:
source. Photons absorbed by the STJ allow quasiparticles to tunnel via the process of photon-assisted tunneling. This photon-assisted tunneling changes the current-voltage curve, creating a nonlinearity that produces an output at the difference frequency of the astronomical signal and the local
186:
exceeds twice the value of superconducting energy gap Δ. At finite temperature, a small quasiparticle tunneling current – called the subgap current – is present even for voltages less than twice the energy gap due to the thermal promotion of quasiparticles above the gap.
615:. The quasiparticles tunnel across the junction in the direction of the applied voltage, and the resulting tunneling current is proportional to the photon energy. STJ devices have been employed as single-photon detectors for photon frequencies ranging from
505:
has a superconducting critical temperature of 7.2 K in bulk form, but lead oxide tends to develop defects (sometimes called pinhole defects) that short-circuit the tunnel barrier when the device is thermally cycled between
846:. These steps provide an exact conversion from frequency to voltage. Because frequency can be measured with very high precision, this effect is used as the basis of the Josephson voltage standard, which implements the
587:
oscillator. This output is a frequency down-converted version of the astronomical signal. These receivers are so sensitive that an accurate description of the device performance must take into account the effects of
115:
states exist for energies greater than Δ from the Fermi energy, where Δ is the superconducting energy gap. Green and blue indicate empty and filled quasiparticle states, respectively, at zero temperature.
214:, the dc current-voltage curve will exhibit both Shapiro steps and steps due to photon-assisted tunneling. Shapiro steps arise from the response of the supercurrent and occur at voltages equal to
107:, indicated by the dashed lines. A bias voltage V is applied across the junction, shifting the Fermi energies of the two superconductors relative to each other by an energy eV, where e is the
1436:
Wu, Heng; Wang, Yaojia; Xu, Yuanfeng; Sivakumar, Pranava K.; Pasco, Chris; Filippozzi, Ulderico; Parkin, Stuart S. P.; Zeng, Yu-Jia; McQueen, Tyrel; Ali, Mazhar N. (2022-04-27).
451:. After the vacuum is restored, an overlapping layer of superconducting metal is deposited, completing the STJ. To create a well-defined overlap region, a procedure known as the
87:
Illustration of a thin-film superconducting tunnel junction (STJ). The superconducting material is light blue, the insulating tunnel barrier is black, and the substrate is green.
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212:
1289:
Likharev, K.K.; Semenov, V.K. (1991). "RSFQ logic/memory family: a new
Josephson-junction technology for sub-terahertz-clock-frequency digital systems".
481:. For many applications, it is convenient to have a device that is superconducting at a higher temperature, in particular at a temperature above the
1348:
603:
detection, STJs can also be used as direct detectors. In this application, the STJ is biased with a dc voltage less than the gap voltage. A
895:
632:
465:
is widely used for making superconducting tunnel junctions because of its unique ability to form a very thin (2–3 nm) insulating
975:
Shapiro, Sidney (1963-07-15). "Josephson
Currents in Superconducting Tunneling: The Effect of Microwaves and Other Observations".
497:
by the thicker niobium, and the resulting device has a superconducting critical temperature above 4.2 K. Early work used
1138:
Zmuidzinas, J.; Richards, P.L. (2004). "Superconducting detectors and mixers for millimeter and submillimeter astrophysics".
494:
329:. Photon-assisted tunneling arises from the response of the quasiparticles and gives rise to steps displaced in voltage by
1530:
456:
901:
655:
72:
95:
Energy diagram of a superconducting tunnel junction. The vertical axis is energy, and the horizontal axis shows the
372:
885:
1525:
912:
56:
1545:
639:
is based on a superconducting loop containing
Josephson junctions. SQUIDs are the world's most sensitive
582:). A high frequency signal from an astronomical object of interest is focused onto the STJ, along with a
1515:
1520:
906:
698:
679:
60:
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538:
1540:
452:
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163:
current, which, in the limit of zero temperature, arises when the energy from the bias voltage
156:
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gas is then introduced into the chamber, resulting in the formation of an insulating layer of
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984:
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332:
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424:
398:
8:
1181:
Wengler, M.J. (1992). "Submillimeter-wave detection with superconducting tunnel diodes".
862:
In the case that the STJ shows asymmetric
Josephson tunneling, the junction can become a
143:. There are two components to the tunneling current. The first is from the tunneling of
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1386:
1302:
1247:
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1051:
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489:, which is 4.2 K at atmospheric pressure. One approach to achieving this is to use
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receivers in the 100 GHz to 1000 GHz frequency range, and hence are used for
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45:
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1326:
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123:
Sketch of the current–voltage (I–V) curve of a superconducting tunnel junction. The
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temperatures and room temperature, so lead is no longer widely used to make STJs.
83:
52:, though not all the properties of the STJ are described by the Josephson effect.
863:
528:
474:
278:
37:
1437:
1471:
612:
466:
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384:
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996:
932:
Josephson, B.D. (1962). "Possible new effects in superconductive tunnelling".
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flowing through the STJ pass through the insulating layer via the process of
128:
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1203:
1091:"Low-noise 115-GHz mixing in superconducting oxide-barrier tunnel junctions"
55:
These devices have a wide range of applications, including high-sensitivity
1487:
1394:
1242:(11). Institute of Electrical and Electronics Engineers (IEEE): 1234–1258.
1189:(11). Institute of Electrical and Electronics Engineers (IEEE): 1810–1826.
1146:(10). Institute of Electrical and Electronics Engineers (IEEE): 1597–1616.
659:
640:
608:
144:
104:
100:
1234:
Tucker, J. (1979). "Quantum limited detection in tunnel junction mixers".
1381:(12). Institute of Electrical and Electronics Engineers (IEEE): 623–625.
667:
124:
33:
1046:(2). Institute of Electrical and Electronics Engineers (IEEE): 106–109.
663:
600:
524:
1310:
1297:(1). Institute of Electrical and Electronics Engineers (IEEE): 3–28.
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507:
448:
91:
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1115:
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1454:
1438:"The field-free Josephson diode in a van der Waals heterostructure"
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by first depositing a thin film of a superconducting metal such as
302:
108:
532:
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380:
326:
191:
44:
material. Current passes through the junction via the process of
1369:
Hamilton, C.A.; Kautz, R.L.; Steiner, R.L.; Lloyd, F.L. (1985).
616:
604:
478:
388:
119:
1031:
Joseph, A.A.; Sese, J.; Flokstra, J.; Kerkhoff, H.G. (2005).
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64:
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is commonly used. This technique uses a suspended bridge of
851:
683:
502:
498:
477:
critical temperature of aluminum is approximately 1.2
131:
tunneling current is seen for V > 2Δ/e and V < -2Δ/e.
68:
1030:
1368:
1345:
The NIST Reference on
Constants, Units, and Uncertainty
847:
459:
with a double-angle deposition to define the junction.
26:
superconductor–insulator–superconductor tunnel junction
531:
at these frequencies. In this application, the STJ is
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311:
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220:
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in 1962. For this prediction, Josephson received the
1089:
Dolan, G. J.; Phillips, T. G.; Woody, D. P. (1979).
773:
is the applied frequency and the
Josephson constant
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1088:
1033:"Structural Testing of the HYPRES Niobium Process"
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147:. This supercurrent is described by the ac and dc
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1507:
1371:"A practical Josephson voltage standard at 1 V"
1288:
1291:IEEE Transactions on Applied Superconductivity
1040:IEEE Transactions on Applied Superconductivity
127:tunneling current is seen at V = 0, while the
983:(2). American Physical Society (APS): 80–82.
689:
1333:
1277:STJ detectors from the European Space Agency
896:Superconducting quantum interference device
633:superconducting quantum interference device
594:
1453:
1202:
1114:
931:
678:The STJ is the primary active element in
535:at a voltage just below the gap voltage (
118:
90:
82:
1341:"2022 CODATA Value: Josephson constant"
1180:
1021:, 2nd edition, Dover Publications, 1996
974:
658:utilizes STJ-based circuits, including
383:. The deposition is performed inside a
1508:
1233:
607:absorbed in the superconductor breaks
447:) with a typical thickness of several
366:
650:
78:
1236:IEEE Journal of Quantum Electronics
501:-lead oxide-lead tunnel junctions.
379:on an insulating substrate such as
13:
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561:
518:
40:separated by a very thin layer of
14:
1557:
1424:Quantum voltage metrology at NIST
1019:Introduction to Superconductivity
902:Superconducting quantum computing
656:Superconducting quantum computing
643:, capable of measuring a single
1429:
1417:
1362:
1282:
815:is a constant that is equal to
726:{\displaystyle nf/K_{\text{J}}}
513:
18:superconducting tunnel junction
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1227:
1174:
1131:
1101:(5). AIP Publishing: 347–349.
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1024:
1011:
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575:{\displaystyle |V|=2\Delta /e}
551:
543:
244:
235:
190:If the STJ is irradiated with
1:
918:
886:Macroscopic quantum phenomena
363:relative to the gap voltage.
1375:IEEE Electron Device Letters
954:10.1016/0031-9163(62)91369-0
913:Cryogenic particle detectors
793:{\displaystyle K_{\text{J}}}
523:STJs are the most sensitive
7:
940:(7). Elsevier BV: 251–253.
869:
469:layer with no defects that
159:in 1973. The second is the
10:
1562:
1472:10.1038/s41586-022-04504-8
690:Josephson voltage standard
473:the insulating layer. The
69:high speed digital circuit
1531:Superconducting detectors
1152:10.1109/jproc.2004.833670
997:10.1103/physrevlett.11.80
907:Rapid single flux quantum
680:rapid single flux quantum
626:
61:electromagnetic radiation
36:device consisting of two
1256:10.1109/jqe.1979.1069931
1060:10.1109/tasc.2005.849705
453:Niemeyer-Dolan technique
371:The device is typically
250:{\displaystyle nhf/(2e)}
1183:Proceedings of the IEEE
1140:Proceedings of the IEEE
1095:Applied Physics Letters
977:Physical Review Letters
673:
595:Single-photon detection
48:. The STJ is a type of
1395:10.1109/edl.1985.26253
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157:Nobel prize in physics
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645:magnetic flux quantum
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356:{\displaystyle nhf/e}
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153:Brian David Josephson
151:, first predicted by
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839:{\displaystyle 2e/h}
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440:{\displaystyle _{3}}
425:
414:{\displaystyle _{2}}
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24:) – also known as a
1526:Quantum electronics
1464:2022Natur.604..653W
1387:1985IEDL....6..623H
1303:1991ITAS....1....3L
1248:1979IJQE...15.1234T
1107:1979ApPhL..34..347D
1052:2005ITAS...15..106J
989:1963PhRvL..11...80S
946:1962PhL.....1..251J
149:Josephson relations
1546:Mesoscopic physics
1426:, accessed 11-5-11
1279:, accessed 8-17-11
850:definition of the
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367:Device fabrication
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179:{\displaystyle eV}
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50:Josephson junction
1516:Superconductivity
1448:(7907): 653–656.
891:Quantum tunneling
876:Superconductivity
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766:{\displaystyle f}
746:{\displaystyle n}
720:
651:Quantum computing
318:{\displaystyle n}
294:{\displaystyle e}
270:{\displaystyle h}
207:{\displaystyle f}
141:quantum tunneling
97:density of states
79:Quantum tunneling
73:quantum computing
46:quantum tunneling
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810:10 Hzâ‹…V
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668:phase qubits
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611:and creates
609:Cooper pairs
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522:
514:Applications
495:proximitized
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305:charge, and
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145:Cooper pairs
134:
105:Fermi energy
101:Cooper pairs
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29:
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664:flux qubits
125:Cooper pair
1510:Categories
1455:2103.15809
1355:2024-05-18
1351:. May 2024
919:References
601:heterodyne
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