1. Pitch and Catch of Non-Classical Microwaves
PI’s:
Rob Schoelkopf
Liang Jiang Michel Devoret
Students/postdocs:
Wolfgang Pfaff
Chris Axline
Luke Burkhart
Jianming Wen
Changling Zhou
Linshu Li
Phil Reinhold
Marius Constantin
Chris Wang
Menghen Zhang
Disclosure: RS and MD are co-founders, consultants, and equity holders at Quantum Circuits, Inc.

2. Wiring up quantum systems with mechanical oscillators

3. Quantum state transfer between transmon qubits and microwave circuits
Roles in collaboration:
Assist w/ SC qubit + mechanics integration
Develop source of on-demand, non-classical propagating m-wave states
Demonstrate all m-wave state transfer
Perform error-corrected state transfer
Demo transduction of non-classical states

4. Quantum state transfer between transmon qubits and microwave circuits
Roles in collaboration:
Assist w/ SC qubit + mechanics integration
Develop source of on-demand, non-classical propagating m-wave states
Demonstrate all m-wave state transfer
Perform error-corrected state transfer
Demo transduction of non-classical states
W. Pfaff et al., in preparation!

5. Overview Intro to “Pitch and Catch” for quantum state transfer
Using a microwave-driven transmon as a Q-switch
Collecting flying quantum states with a JPC amplifier
Demonstration of high-fidelity conversion of standing to flying states
Future plans for pitch and catch

6. Vision: Cavity QED Quantum Network
Goal: Transfer and route interesting cavity states.
Two-level system required for state preparation and tomography.
(J. Kimble, 2008)

7. Near-term Goal: ”Pitch & Catch”

8. Expts. Towards P&C with SC Circuits
Princeton: Houck group
UCSB: Martinis/Cleland group
Srinivasan et al., PRA 2014
Wenner et al., PRL 2014
Tunable coupling qubit (double transmon): adjust dipole moment to shape emission
Zurich: Wallraff group
Flux-tunable resonator coupling (Q) adjust absorption to catch
Pechal et al., arXiv
No actual transfer of non-classical states demonstrated so far …
All-RF shaping of emission using higher levels of transmon

9. Desired Characteristics of Quantum Source
Launches complex quantum states on demand
Control over temporal waveform
Match to converter bandwidth: 104 – 106 Hz
Applicable to a variety of non-classical states
Fock states, cats for error correction, …
High contrast (on/off ratio)
High fidelity – preserves coherences

10. 3D cavities for module-based scaling
seamless modules, integration of ms-coherence memory cavities
combines 3D cavities with qubit/stripline chips
versions in use with ~ 5 qubits and ~ 10 cavities
Axline et. al., APL 109 (4), (2016)

11. Complex Ops. thru Optimal Control
(Heeres, et al., arXiv )
GRAPE
Realize | 6 0| to make Fock state | 6 ?
Cavity
Transmon

12. Implementing a Node in cQED
Qubit = artificial Kerr medium*
* as in many JJ parametric amplifiers
“controllable beam-splitter or converter”

13. Implementing a Node in cQED
0.64 MHz means decay time of b mode is 250 nanoseconds
Idea: Switch coupling on/off w/ RF signals turning on parametric conversion using the non-linearity of the qubit.
During/after conversion, the field leaks from the low-Q mode into the transmission line.

14. First Milestone: Pitch Cavity States
JPC amplifier courtesy of
Devoret group
First, use this chain
to measure qubit
and monitor the state remaining in storage cavity…

15. Evacuation of the Memory Cavity

16. Evacuation of the Memory Cavity

17. 3 Orders of Magnitude Tuning Range
Exact model
(no free params,
independent
calibrations of g)
Approximation:
g large enough to see onset of non-exponential decay
Fastest evacuation rate achieved so far ~ 1/500 ns, close to being limited by the low-Q resonator

18. Evacuation is State-Independent
Solid lines: theory with independently calibrated g
m = 2
n = 0
n = 2
n = 1
Time (ms) 40

19. Evacuation is State-Independent
Solid lines: theory with independently calibrated g
m = 2
m = 5
n = 0
n = 2
n = 1
n = 3
n = 4
n = 5

20. First Milestone: Pitch Cavity States
Analyze flying states out using JPC courtesy
Devoret group

21. Cavity Field is Emitted Coherently

22. Cavity Field is Emitted Coherently

23. Cavity Field is Emitted Coherently

24. Cavity Field is Emitted Coherently
Q-functions of flying states
Detection efficiency here ~ 47%
raw data
sim.

25. Fock-State Superpositions 0+n
Intra-cavity Wigner functions
n = 1
n = 2
n = 3
n = 4
n = 5
Detected propagating fields
aw data
Radial integral clearly shows n-fold symmetry. Solid line: theory, only assuming loss.

26. Entanglement by Half-Pitching
1) Pitch half the energy in the cavity.
2) Correlate the traveling field with measurement of standing state remaining.
Cavity found in 0
Cavity found in 1
Cavity found in 0+1
Cavity found in 0-1
Pump
Pump

27. Summary
Two cavity/one qubit modules as generator/analyzers of quantum states
Demonstrated RF-activated “Q-switching” to pitch states
On/off ratio now almost 1,000x
Pitching preserves coherence
Estimated efficiency is of order unity.
Damping is photon independent.
Pitching works even for complex multiphoton states
Future plans: shaping temporal wavepacket full microwave pitch and catch between two modules use a source to measure efficiency of optical transducer pitching an encoded logical qubit?

28. end

29. Fidelity of Logical Qubit Operations
Interleaved randomized benchmarking
Heeres, et al., arXiv
data!
data!
data!
Gate
Fidelity (%)
<all>
99.1 I
99.5
X90
99.2
-X90
X180
98.9
Y90
-Y90
Y180
98.7 H
Dec/enc
98.3
X90
X90