Spectroscopy of Andreev States in superconducting atomic contacts

Transcription

1 Spectroscopy of Andreev States in superconducting atomic contacts Landry Bretheau and Ç. Girit H. Pothier OPERATION CONTACT ATOMIQUE Sale temps pour les raies D. Esteve C. Urbina Quantronics Group, CEA-Saclay

2 ANDREEV BOUND STATES IN 1 CHANNEL WEAK LINK Phase-biased short, single channel L < x L R L R Analogous to Fabry-Perot

3 ANDREEV BOUND STATES IN 1 CHANNEL WEAK LINK Phase-biased short, single channel L R L < x t = 1 L R Analogous to Fabry-Perot

4 ANDREEV BOUND STATES IN 1 CHANNEL WEAK LINK Phase-biased short, single channel L R L < x t < 1 L R Analogous to Fabry-Perot

5 ANDREEV BOUND STATES in a spin degenerate, short reflective single channel (t <1 ) L R E +D 4 -D

6 ANDREEV BOUND STATES in a spin degenerate, short reflective single channel (t <1 ) L R E() Andreev spectrum E +D +E A +D 2D 1t 2 4 -D -E A -D E A D t 2 1 sin 2 I( ) 1 E Furusaki, Tsukada C.W.J. Beenakker (1991)

7 SUPERCONDUCTING ATOMIC CONTACTS V S S I 1 atom contact = few conduction channels (Al: 3) Tunable t,..., t 1 N measurable Stable

8 MICROFABRICATED BREAK-JUNCTIONS 2 µm Aluminium suspended bridge metallic film pushing rods insulating layer countersupport Flexible substrate Pushing rod Elastic substrate

9 I (na) I(V) OF A ONE-ATOM-CONTACT I (µa) 6 V / (D/e) V (µv) V (µv)

10 I (na) DETERMINATION OF CHANNELS TRANSMISSIONS 6 V / (D/e) {.47,.24,.5} V (µv) I(V) characteristic t 1,..., t N Scheer et al. PRL 1997

11 BIASING A CONTACT PHASE BIASING TO DEFINE ANDREEV STATES Tuning of E( ) B : spectroscopy VOLTAGE BIASING TO DETERMINE TRANSMISSIONS I ( V ) measurement t,..., t 1 N V

12 I (µa) A SUPERCONDUCTING REVERSIBLE SWITCH I I Tuning of E( ) : spectroscopy I b B B SHORT I ( V ) measurement t,..., t 1 N 1 SHORT V I b OPEN V (µv) OPEN

13 ATOMIC SQUID I R b I V b 2 5 µm

14 PROBING ANDREEV BOUND STATES GROUND STATE Already probed through supercurrent measurement in superconducting atomic contacts Della Rocca et al. PRL (27)

15 Related but Pillet et al. Nature Physics (21) PROBING ANDREEV BOUND STATES EXCITED STATE? +D E +E A Microwave irradiation 2 -D -E A

16 frequency (GHz) ORDERS OF MAGNITUDE FOR ALUMINUM +D E +E A h 2 E ( ) 2 A Shine microwaves? -D -E A 1 8 t= t= t=.99

17 frequency (GHz) ORDERS OF MAGNITUDE FOR ALUMINUM +D E +E A h 2 E ( ) 2 A Shine microwaves? -D -E A t=.5 Wide band microwave spectroscopy in a Cryogenic system HARD 4 t=.9 Relatively easy up to 2 GHz 2 2 t=.99 - only large transmissions - only around

18 JOSEPHSON JUNCTION AS BOTH RF CURRENT GENERATOR AND DETECTOR on-chip RF generator DC Voltage biased Josephson junction r AC Josephson effect V b I JJ I I d dt JJ sin 2eV JJ At first order : JJ 2e V h JJ I I JJ JJ sin(2 t)

19 JOSEPHSON JUNCTION AS BOTH RF CURRENT GENERATOR AND DETECTOR DC Voltage biased Josephson junction on-chip RF generator and detector r AC Josephson effect E Environment V b I JJ At first order : JJ I I d dt JJ sin 2eV 2e V h JJ JJ JJ Cooper pair V JJ I I JJ JJ sin(2 t) DC current peak if photon absorbed by environment

20 THE JOSEPHSON JUNCTION SPECTROMETER Photon JJ absorbed by the environment JJ 2e V h JJ 2 DC current peak I JJ (na) Δ/e 2Δ/e V JJ (µv)

21 THE JOSEPHSON JUNCTION SPECTROMETER Photon JJ absorbed by the environment V b r JJ 2e V Z(ω) h JJ I JJ (na) Δ/e DC current peak 2Δ/e -2 Spectrometer Environment -2 2 V JJ (µv) - On-chip irradiation - DC Tunable microwave emitter / DC response - Frequency range up to 4D = 2GHz - JJ is also detector

22 SPECTROSCOPY OF THE ANDREEV 2 LEVEL SYSTEM JJ r V b V JJ +D E +E A h 2 E ( ) JJ 2 A -D -E A fermionic modes

23 L {t i } CIRCUIT C I I JJ V JJ L L~few nh C~3pF U b Atomic SQUID Spectrometry Junction V b

24 L {t i } CIRCUIT C I I JJ V JJ L L~few nh C~3pF U b Atomic SQUID Spectrometry Junction V b DC caracterisation of atomic contact {t i } Atomic SQUID I U b

25 L {t i } CIRCUIT C I I JJ V JJ L L~few nh C~3pF U b Atomic SQUID Spectrometry Junction V b RF excitation of Andreev 2LS C JJ =2eV JJ /h V b

26 L {t i } CIRCUIT C I I JJ V JJ L r b L~few nh C~3pF U b V b Atomic SQUID Spectrometry Junction RF excitation of Andreev 2LS + measurement of I C JJ, V JJ r b r b I JJ V b V JJ

27 5 µm SAMPLE C 1µm 1µm

28 JUNCTION IV 1 AC formed 2 1 I JJ (na) V JJ (µv)

29 JUNCTION IV 1 AC formed I JJ (na) V JJ (µv) 15 2

30 JUNCTION IV 1 AC formed I JJ (na) V JJ (µv) 15 2

31 AC1 JUNCTION d IJJ (,V ) JJ d MAP 2 D/e V JJ (µv) p 15GHz 28µV 2

32 AC1 JUNCTION AC2 d IJJ (,V ) JJ d MAP 2 D/e V JJ (µv)

33 AC1 JUNCTION AC2 d IJJ (,V ) JJ d MAP AC3 2 D/e V JJ (µv)

34 AC1 JUNCTION AC2 d IJJ (,V ) JJ d MAP AC3 AC4 2 D/e V JJ (µv)

35 AC1 JUNCTION d IJJ (,V ) JJ d MAP 2 D/e V JJ (µv)

36 AC1 JUNCTION d IJJ (,V ) JJ d MAP 2 D/e {.72} Compatible with MAR V JJ (µv)

37 AC3 JUNCTION d IJJ (,V ) JJ d MAP 2 D/e V JJ (µv)

38 AC3 JUNCTION d IJJ (,V ) JJ d MAP 2 D/e {.78} Compatible with MAR 14 V JJ (µv)

39 AC3 JUNCTION d IJJ (,V ) JJ d MAP 2 D/e V JJ (µv)

40 AC3 JUNCTION d IJJ (,V ) JJ d MAP 2 D/e {.99,.66} Compatible with MAR V JJ (µv)

41 AC1 JUNCTION d IJJ (,V ) JJ d MAP 2 D/e {.72} Compatible with MAR V JJ (µv)

42 JJ AC1 V 15µV HORIZONTAL CUT 5 I JJ (pa) dijj/d (pa/rad) 2-5

43 JJ AC1 V 15µV HORIZONTAL CUT 5 I JJ (pa) 1 5 dijj/d (pa/rad) 2-5

44 JJ AC1 V 15µV 57GHz JJ ANDREEV PEAKS ~1 pa I JJ (pa) 1 5.8*2 2

45 JJ AC1 V 15µV 57GHz JJ ANDREEV PEAKS ~1 pa I JJ (pa) 1 5.8*2 DE A = 7GHz Lifetime > 14ps 2

46 JJ AC1 V 15µV 57GHz JJ ANDREEV PEAKS G = I/2e= 4MHz ~1 pa I JJ (pa) 1 5.8*2 DE A = 7GHz Lifetime > 14ps 2

47 JJ AC1 V 15µV 57GHz JJ ANDREEV PEAKS G = I/2e= 4MHz limiting process ~1 pa I JJ (pa) 1 5.8*2 DE A = 7GHz Lifetime > 14ps 2

48 CONCLUSIONS We understand: Position of Andreev resonances We don t understand: The other resonances : plasma resonances of the atomic SQUID The shape of the Andreev peaks To do: Decrease I JJ to get rid of parasitic resonances and its harmonics to be continued

49 TOWARDS ANDREEV QUBITS E() +D +E A 2 -D -E A Use even states Zazunov, Shumeiko,Bratus, Lantz and Wendin, PRL (23) Use quasiparticle (spin ½) states Chtchelkatchev and Nazarov, PRL (23)