Analyzing control signals for quantum logic operations in superconducting quantum circuits
In a general aspect, control of a quantum superconducting circuit is analyzed. In some implementation, a parameter set for a control signal for a superconducting quantum circuit is received. The parameters set can include initial voltage amplitudes for respective time segments of the control signal. A first subset of time segments is selected for improving a quality measure of a quantum logic operation produced by delivery of the control signal in the superconducting quantum circuit. New voltage amplitudes are calculated for one or more segments in the first subset, such that the new voltage amplitudes improve the quality measure. The parameter set is updated to include the new voltage amplitudes for the first subset while preserving the initial voltage amplitudes for a second subset of the time segments.
1. A method comprising:
accessing a parameter set for a control signal for a superconducting quantum circuit, the parameter set comprising initial voltage amplitudes for respective time segments of the control signal;
selecting a first subset of the time segments for improving a quality measure of a quantum logic operation produced by delivery of the control signal in the superconducting quantum circuit;
by operation of data processing apparatus, calculating a new voltage amplitude for a first time segment in the first subset, the new voltage amplitude calculated to improve the quality measure; and
updating the parameter set to include the new voltage amplitude for the first time segment while preserving the initial voltage amplitudes for a second subset of the time segments.
2. The method of claim 1 , comprising:
by operation of data processing apparatus, calculating new voltage amplitudes for the time segments in the first subset, the new voltage amplitudes calculated to improve the quality measure; and
updating the parameter set to include the new voltage amplitudes for the first subset of time segments while preserving the initial voltage amplitudes for the second subset of time segments.
3. The method of claim 2 , wherein updating the parameter set produces a first updated parameter set, and the method further comprises producing a second updated parameter set from the first updated parameter set based on evaluating the voltage amplitudes for all time segments to improve the quality measure.
4. The method of claim 2 , comprising performing an iterative process that includes, on each iteration:
selecting time segments for improving a quality measure of the quantum logic operation;
calculating a new voltage amplitude for one or more of the selected time segments, each new voltage amplitude calculated to improve the quality measure; and
updating the parameter set to include the new voltage amplitudes.
5. The method of claim 4 , wherein the iterative process comprises an optimization process configured to optimize the quality measure.
6. The method of claim 1 , wherein the quality measure comprises a quantum process fidelity that represents a comparison between an ideal execution of the quantum logic operation and a simulated execution of the quantum logic operation based on the parameter set.
7. The method of claim 6 , wherein the simulated execution of the quantum logic operation comprises a dissipation model.
8. The method of claim 1 , wherein the quality measure comprises a quantum state fidelity that represents a comparison between an ideal state produced by an ideal execution of the quantum logic operation and a simulated state produce by a simulated execution of the quantum logic operation based on the parameter set.
9. The method of claim 1 , wherein a quantum processor comprises the superconducting quantum circuit, and the quantum logic operation comprises multiple quantum logic gates to be executed by the quantum processor.
10. The method of claim 1 , wherein the superconducting quantum circuit includes a qubit device comprising a Josephson junction, and the quantum logic operation comprises a quantum logic gate for the qubit device.
11. The method of claim 1 , further comprising generating an instance of the control signal for delivery to the superconducting quantum circuit.
12. The method of claim 11 , wherein the instance of the control signal is generated by a digital to analog converter processing the updated parameter set.
13. A system comprising:
a superconducting quantum circuit; and
a control system comprising one or more processors configured to:
access a parameter set for a control signal for the superconducting quantum circuit, the parameter set comprising initial voltage amplitudes for respective time segments of the control signal;
select a first subset of the time segments to evaluate for improving a quality measure of a quantum logic operation produced by delivery of the control signal in the superconducting quantum circuit;
calculate a new voltage amplitude for a first time segment in the first subset, the new voltage amplitude calculated to improve the quality measure; and
update the parameter set to include the new voltage amplitude for the first time segment while preserving the initial voltage amplitudes for a second subset of the time segments.
14. The system of claim 13 , wherein the one or more processors are configured to:
calculate new voltage amplitudes for the time segments in the first subset, the new voltage amplitudes calculated to improve the quality measure;
update the parameter set to include the new voltage amplitudes for the first subset of time segment while preserving the initial voltage amplitudes for the second subset of time segments.
15. The system of claim 13 , wherein the one or more processors are configured to perform an iterative process that includes, on each iteration:
selecting time segments for improving a quality measure of the quantum logic operation; and
calculating a new voltage amplitude for one or more of the selected time segments, each new voltage amplitude calculated to improve the quality measure; and
updating the parameter set to include the new voltage amplitudes.
16. The system of claim 15 , wherein the iterative process comprises an optimization process configured to optimize the quality measure.
17. The system of claim 13 , wherein the quality measure comprises a quantum process fidelity that represents a comparison between an ideal execution of the quantum logic operation and a simulated execution of the quantum logic operation based on the parameter set.
18. The system of claim 17 , wherein the simulated execution of the quantum logic process comprises a dissipation model.
19. The system of claim 13 , wherein the quantum logic operation comprises multiple quantum logic gates.
20. The system of claim 13 , wherein the superconducting quantum circuit includes a qubit device comprising a Josephson junction, and the quality measure is based on a quantum logic gate for the qubit device.
21. The system of claim 20 , wherein the control system is operable to generate an instance of the control signal for delivery to the qubit device.
22. The system of claim 13 , wherein the control system comprises a digital to analog converter configured to generate an instance of the control signal by processing the updated parameter set.