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
PMMA
Copolymer
Silicon
Layers
Suspended bridges
Devices
Mask
e-beam
litography 1
Al evaporation 3
Oxidation 4
Al evaporation 5
Development 2
Lift off 6

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
Cooper Pair Box Qubit
Flux Qubit
Transmon Qubit
Single junction
3 junction flux qubit
Quantronium …

19. Dechoerence Effect of noise from different sources Relaxation T1=1/g1
Dephasing T2=1/g2
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 ≈
Tk ≈ 200 ns
Tg ≈ 230 ns
A. Wallraff et al., Nature 431, 162–167 (2004).

24. Photon number state Q ≈ 30 000 Tk ≈ 640 ns Tg ≈ 84 ns
D. I. Schuster et al., Nature 445,
515–518 (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, 663–667 (2010).

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

27. Double 3D cavities Coherent state Even cat state Odd cat state
B. Vlastakis et al., Deterministically Encoding Quantum Information Using 100-Photon Schrödinger Cat States, Science 342, 607–610 (2013).

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