Resetting qubits in a superconducting quantum processor
In a general aspect, a tunable qubit device is identified that exhibits a frequency-dependent energy relaxation process in a quantum processor cell. The frequency-dependent energy relaxation process is produced by a material defect in the quantum processor cell. A first qubit frequency associated with a first relaxation time of the tunable qubit device is identified and a second qubit frequency associated with a second relaxation time of the tunable qubit device is identified. The second relaxation time is shorter than the first due to the frequency-dependent energy relaxation process produced by the material defect. The tunable qubit device is operated at the first qubit frequency while processing quantum information in the quantum processor cell. The tunable qubit device is tuned from the first qubit frequency to the second qubit frequency. A qubit state of the qubit device is reset by the frequency-dependent energy relaxation process produced by the material defect.
1. A quantum computing method comprising:
identifying a tunable qubit device that exhibits a frequency-dependent energy relaxation process in a quantum processor cell, wherein the frequency-dependent energy relaxation process is produced by a material defect in the quantum processor cell;
identifying a first qubit frequency associated with a first relaxation time of the tunable qubit device;
identifying a second qubit frequency associated with a second relaxation time of the tunable qubit device, wherein the second relaxation time is shorter than the first relaxation time due to the frequency-dependent energy relaxation process produced by the material defect;
operating the tunable qubit device at the first qubit frequency while processing quantum information in the quantum processor cell;
tuning the tunable qubit device from the first qubit frequency to the second qubit frequency; and
resetting a qubit state of the tunable qubit device by the frequency-dependent energy relaxation process produced by the material defect.
2. The method of claim 1 , wherein the quantum processor cell comprises a reset element associated with the tunable qubit device, the reset element comprises the material defect, and tuning the tunable qubit device from the first qubit frequency to the second qubit frequency increases a coupling between the reset element and the tunable qubit device.
3. The method of claim 2 , wherein the quantum processor cell houses a quantum integrated circuit system that includes the tunable qubit device, and the material defect comprises one or more of a lattice defect, a surface defect or a defective hardware element of the quantum integrated circuit system.
4. The method of claim 2 , wherein the quantum processor cell comprises a flux-bias device associated with the tunable qubit device, and tuning the tunable qubit device from the first qubit frequency to the second qubit frequency comprises modifying a current through the flux-bias device.
5. The method of claim 4 , wherein the tunable qubit device, the reset element, and the flux-bias device are disposed on a substrate, and the material defect comprises a lattice defect in a crystal structure of the substrate or a surface defect near a surface of the substrate.
6. The method of claim 1 , wherein the second relaxation time is less than one tenth of the first relaxation time.
7. The method of claim 1 , wherein the second relaxation time is less than one hundredth of the first relaxation time.
8. The method of claim 1 , wherein resetting the qubit state comprises holding the tunable qubit device at the second qubit frequency for a specified amount of time.
9. The method of claim 1 , wherein resetting the qubit state transitions the tunable qubit device to its ground state.
10. The method of claim 1 , wherein the first relaxation time is greater than or equal to 10 microseconds (μs).
11. The method of claim 10 , wherein the second relaxation time is less than or equal to 1 microsecond (μs).
12. A quantum computing system comprising:
a quantum processor cell comprising a plurality of qubit devices, the plurality of qubit devices comprising one or more tunable qubit devices; and
a control system communicably coupled to the quantum processor cell and configured to perform operations comprising:
identifying a tunable qubit device in the plurality of qubit devices that exhibits a frequency-dependent energy relaxation process in the quantum processor cell, wherein the frequency-dependent energy relaxation process is produced by a material defect in the quantum processor cell,
identifying a first qubit frequency associated with a first relaxation time of the tunable qubit device,
identifying a second qubit frequency associated with a second relaxation time of the tunable qubit device, wherein the second relaxation time is shorter than the first relaxation time due to the frequency-dependent energy relaxation process produced by the material defect,
operating the tunable qubit device at the first qubit frequency while processing quantum information in the quantum processor cell,
tuning the tunable qubit device from the first qubit frequency to the second qubit frequency, and
resetting a qubit state of the tunable qubit device by the frequency-dependent energy relaxation process produced by the material defect.
13. The quantum computing system of claim 12 , wherein the quantum processor cell comprises a reset element associated with the tunable qubit device, the reset element comprises the material defect, and tuning the tunable qubit device from the first qubit frequency to the second qubit frequency increases a coupling between the reset element and the tunable qubit device.
14. The quantum computing system of claim 13 , wherein the quantum processor cell houses a quantum integrated circuit system that includes the tunable qubit device, and the material defect comprises one or more of a lattice defect, a surface defect or a defective hardware element of the quantum integrated circuit system.
15. The quantum computing system of claim 13 , wherein the quantum processor cell comprises a flux-bias device associated with the tunable qubit device, and tuning the tunable qubit device from the first qubit frequency to the second qubit frequency comprises modifying a current through the flux-bias device.
16. The quantum computing system of claim 15 , wherein the tunable qubit device, the reset element, and the flux-bias device are disposed on a substrate, and the material defect comprises a lattice defect in a crystal structure of the substrate or a surface defect near a surface of the substrate.
17. The quantum computing system of claim 12 , wherein the second relaxation time is less than one tenth of the first relaxation time.
18. The quantum computing system of claim 12 , wherein the second relaxation time is less than one hundredth of the first relaxation time.
19. The quantum computing system of claim 12 , wherein resetting the qubit state comprises holding the tunable qubit device at the second qubit frequency for a specified amount of time.
20. The quantum computing system of claim 12 , wherein resetting the qubit state transitions the tunable qubit device to its ground state.
21. The quantum computing system of claim 12 , wherein the first relaxation time is greater than or equal to 10 microseconds (μs).
22. The quantum computing system of claim 21 , wherein the second relaxation time is less than or equal to 1 microsecond (μs).
23. The quantum computing system of claim 12 , comprising:
a logic flux bias device electromagnetically-coupled to the tunable qubit device and configured to apply a first range of magnetic flux bias to the tunable qubit device; and
a reset flux bias device configured to apply a second range of magnetic flux bias to the tunable qubit device that is broader than the first range of magnetic flux bias.