Superconducting Qubits

Transcription

1 Superconducting Qubits Fabio Chiarello Institute for Photonics and Nanotechnologies IFN CNR Rome

2 Lego bricks The Josephson s Lego bricks box

3 Josephson junction Phase difference Josephson equations Insulating barrier Symbol

4 Josephson junction RCSJ model Phase difference Josephson equations Insulating barrier Mechanical equivalent

5 Josephson junction mechanical equivalent Motion equations Effective potential

6 Superconducting loop

7 rf SQUID Motion equations Effective potential

8 rf SQUID effective potential Torrioli s talk on SQUIDs at 16:00

9 dc SQUID Tunable Josephson element For Torrioli s talk on SQUIDs at 16:00

10 double SQUID Tunable rf SQUID - two controls Large loop: symmetry Small loop: barrier

11 Quantum Electronics Flux quantization Inductance Josephson junction Capacitance

12 Charge regime For control on single Cooper pair crossing (small junctions)

13 Charge regime For control on single Cooper pair crossing SET Transistor Cooper Pair Box Flux of Cooper pairs controlled one by one Can store a single Cooper pair

14 Small Al junctions fabrication Layers Suspended bridges Devices Mask PMMA Copolymer Silicon e-beam litography Development Al evaporation Oxidation Al evaporation Lift off

15 Quantum behavior Quantum behavior

16 Quantum description Is it possible a quantum description of the equivalent mechanical model? Classical description Quantum description P.W. Anderson, in: E.R. Caianiello (Ed.), Lectures on the Many Body Problem, Vol. 2, Academic Press, New York, 1964.

17 Quantum effects (observed) Observed quantum effects in Josephson systems Tunnel Effect Energy Level Quantization Rabi Oscillations Spectroscopy Nonadiabatic manipulation Block Sphere manipulation Entagled Systems (Ramsey fringes, Spin Echo, )

18 Superconducting Qubits Qubit: quantum two state systems which can be manipulated and coupled Flux Qubit Cooper Pair Box Qubit Transmon Qubit Single junction 3 junction flux qubit Quantronium

19 Dechoerence Effect of noise from different sources Relaxation T 1 =1/g 1 Dephasing T 2 =1/g 2 Ohmic noise

20 Single photon detection

21 Single photon detector Absorption of a single (GHz) photon Detection of the qubit state Artificial atom Lambda transition Activation in voltage state

22 Circuit QED Cavity: coplanar waveguide Atom: Cooper pair box qubit Jaynes-Cummings Hamiltonian Tuned Detuned A. Blais, et al., Phys. Rev. A 69, (2004).

23 Circuit QED Coupling between an artificial atom and a cavity Cavity: coplanar waveguide Atom: Cooper pair box qubit Q T k 200 ns T g 230 ns A. Wallraff et al., Nature 431, (2004).

24 Photon number state Q T k 640 ns T g 84 ns D. I. Schuster et al., Nature 445, (2007).

25 QND Detection of single microwave photon Fast qubit readout and reset 0/1 photon (to be counted) 90% QND B. R. Johnson et al., Quantum non-demolition detection of single microwave photons in a circuit, Nat Phys 6, (2010).

26 3D cavity Qubit in a 3D cavity Q T k 20 ms T g 20 ms H. Paik, Phys. Rev. Lett. 107 (2011). First efforts to use a similar system for axions Akash Dixit Aaron Chou Dave Schuster University of Chicago

27 Double 3D cavities Coherent state Even cat state B. Vlastakis et al., Deterministically Encoding Quantum Information Using 100-Photon Schrödinger Cat States, Science 342, (2013). Odd cat state

28 Conclusions Josephson devices: Realization of flexible systems Quantum behavior Detection of single photons at 10 GHz Coupling with cavities at 10 GHz Thank you!