1. Quantum dynamics in nano Josephson junctions Equipe cohérence quantique CNRS – Université Joseph Fourier Institut Néel GRENOBLE Wiebke Guichard Olivier Buisson Frank Hekking Laurent Lévy Bernard Pannetier Aurélien Fay Ioan Pop Florent Lecocq Rapaël Léone Emile Hoskinson Scientific collaborations: PTB Braunschweig ( Germany) LTL Helsinki (Finland) KTH Stockholm (Sweden) Rutgers, New Jersey

2. Research Topics  dc IxIx  (t) Quantum dynamics of an anharmonic oscillator (DC SQUID) Phase qubit Rhombi chain: A novel topologically protected qubit Phase qubit coupled to a charge qubit: Tunable coupling Vg2 Vg1 Cooper pair pumping through a double Island

3.  RF IpIp  DC  nano dc SQUID as a quantum anharmonic oscillator P = +6 dBm    = 260 MHz T mw (ns) P esc 020406080 0.2 0.4 0.6 0.8 Rabi like oscillations: 0 50 100 150 200 250 050100150200250300  1 /2  (MHz) R (MHz) 2-level 01 - 12 234 # involved levels  p (I b,  b )  U (I b,  b ) 10 GHz ~ 500 mK Cross-over macroscopic regime Quantum measurements PRB 76, 024508 (2007) Decoherence processes PRB 73, 180502 (2006) Coherent oscillations PRL 93 187003 (2004) Cond-mat 0709.3787 T 2,Rabi =25ns

4. dc SQUID as a phase qubit  1 /2  (arb. units) R (MHz) T mw (ns) P esc 1) MW excitation I MW on current bias line 2) Quantum measurement: nanosecond flux pulse projects qubit states onto SQUID flux states. |0> |1> 3) Read out: voltage switching using a slow current pulse     qubit Flux state New experimental procedure at zero current bias: Nb Two level limits Anharmonicity~300MHz (collaboration with PTB-Germany) T 1 ~100ns E. Hoskinson unpublished

5. Two quantum systems |0  |1  |2  MW  p (I p,  dc )  U (I p,  dc )  VgVg SQUID dc ACPT Phase qubit charge-phase qubit

6. Asymmetric Cooper pair transistor (Charge qubit) Superconducting island ~ 0.06  m 2 Gate V G I bias Coupled circuit dc SQUID (Phase qubit) SQUID Josephson junction size~ 10  m² Transistor Josephson junction size~ 0.02  m²

7. Spectroscopy measurement of the two quantum systems SQUID CPT

8. Resonant read out of the charge qubit Microwave VGVG  A. Fay unpublished

9. Tunable coupling r = 10.4 GHz g = 0.9 GHz g = 115 MHz r = 18.98 GHz A. Fay unpublished

10. Rhombi chain: a novel topologically protected qubit At  =0.5  0 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) N Rhombi  E  /2 -  /2

11. Switching current measurement S = 618 μm 2 s = 6,98 μm 2 S G = 605 μm 2 s G = 6,84 μm 2 Magnetic field (Gauss) Critical current (nA) E J /E C =2

12. Switching current measurements B. Pannetier et al. to be published E J /E C ~20 At E J /E C ~2

13. 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