Quantum dynamics in nano Josephson junctions

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Quantum dynamics in nano Josephson junctions
Aurélien Fay Ioan Pop Florent Lecocq Rapaël
Léone Emile Hoskinson
Wiebke Guichard Olivier Buisson Frank
Hekking Laurent Lévy Bernard Pannetier
Equipe cohérence quantiqueCNRS Université
Joseph FourierInstitut Néel GRENOBLE
Scientific collaborations PTB Braunschweig (
Germany) LTL Helsinki (Finland)
KTH Stockholm (Sweden) Rutgers, New Jersey
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Research Topics
Phase qubit coupled to a charge qubit Tunable
coupling
Quantum dynamics of an anharmonic
oscillator (DC SQUID) Phase qubit
?(t)
Ix
?dc
Cooper pair pumping through a double Island
Rhombi chain A novel
topologically protected qubit
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dc SQUID as a quantum anharmonic oscillator
Cond-mat 0709.3787
Rabi like oscillations
involved levels
P 6 dBm W1/2p 260 MHz
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3
4
Pesc
2-level
macroscopic regime
nR (MHz)
Cross-over
T2,Rabi25ns
n01-n12
Tmw (ns)
Quantum measurements PRB 76, 024508
(2007) Decoherence processes PRB 73, 180502
(2006) Coherent oscillations PRL 93 187003 (2004)
W1/2p (MHz)
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dc SQUID as a phase qubit
New experimental procedure at zero current bias
1) MW excitation IMW on current bias line 2)
Quantum measurement nanosecond flux pulse
projects qubit states onto SQUID flux states.
0gt 1gt 3) Read out voltage switching
using a slow current pulse
Nb
???
qubit
Flux state
???
(collaboration with PTB-Germany)
Anharmonicity300MHz
T1100ns
Pesc
nR (MHz)
Two level limits
E. Hoskinson unpublished
Tmw (ns)
W1/2p (arb. units)
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Two quantum systems
SQUID dc
ACPT
charge-phase qubit
Phase qubit
Vg
?
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Coupled circuit
dc SQUID (Phase qubit)
Asymmetric Cooper pair transistor (Charge qubit)
Superconducting island 0.06 mm2
Ibias
Gate VG

• SQUID Josephson junction size 10 mm²
• Transistor Josephson junction size 0.02 mm²

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Spectroscopy measurement of the two quantum
systems
CPT
SQUID
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Resonant read out of the charge qubit
VG
d
Microwave
A. Fay unpublished
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Tunable coupling
?r 18.98 GHz
g 115 MHz
?r 10.4 GHz
g 0.9 GHz
A. Fay unpublished
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Rhombi chain a novel topologically protected
qubit
At ?0.5?0
N Rhombi
E
?
B. Doucot et al., Phys. Rev B 71, 024505
(2005) I.Protopopov et al., Phys. Rev B 74,
064516 (2006) L.Ioffe et al. Nature, 415, 503,
(2002)
?/2
-?/2
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Switching current measurement
EJ/EC2
Critical current (nA)
S 618 µm2 s 6,98 µm2
SG 605 µm2 sG 6,84 µm2
Magnetic field (Gauss)
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Switching current measurements
At
EJ/EC2
EJ/EC20
B. Pannetier et al. to be published
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Conclusion

• Quantum dynamics of an anharmonic oscillator in a
  DC SQUID
• Phase qubit
• Tunable coupling between a charge qubit coupled
  and a phase qubit
• Rhombi chain topologically protected qubit