OPERATING A COUPLER DEVICE TO PERFORM QUANTUM LOGIC GATES

• US 20170230050A1
• Filed: 12/22/2015
• Published: 08/10/2017
• Est. Priority Date: 12/22/2015
• Status: Active Grant

• Current Assignee: Rigetti & Co., Inc.
• Original Assignee: Rigetti & Co., Inc.
• Inventors: Rigetti, Chad Tyler, Sete, Eyob A.
• Granted Patent: US 10,056,908 B2
• Time in Patent Office: Days
• CPC Class Codes: G01R 33/02 Measuring direction or magnitude of magnetic fields or magnetic flux G01R33/20 takes precedence
• CPC Class Codes: G06F 13/4068 Electrical coupling
• CPC Class Codes: G06N 10/00 Quantum computing, i.e. information processing based on quantum-mechanical phenomena
• CPC Class Codes: H03K 19/195 using superconductive devices
• CPC Class Codes: H04L 9/0852 Quantum cryptography transmission systems employing electromagnetic waves other than radio waves, e.g. light, infrared H04B10/00; wavelength-division multiplex systems H04J14/02; WDM arrangements H04J14/03

Abstract

In a general aspect, a quantum logic gate can be performed by tuning a coupler device. One or more coupler control signals can be received at a coupler device in a quantum processor cell. In some instances, in response to the coupler control signals, a coupler operating frequency of the coupler device changes toward a qubit operating frequency of a qubit device, and a phase shift arises in a quantum state of the qubit device due to an interaction between the qubit device and the coupler device. In some instances, in response to the control signals, the coupler operating frequency changes toward a first qubit operating frequency of a first qubit device, then changes toward a second qubit operating frequency of a second qubit device, and a controlled-phase shift arises in a quantum state of the qubit devices due to interactions between the coupler device and the respective qubit devices.

Claims

1. A quantum information control method for performing a quantum logic gate, the method comprising:

receiving a coupler control signal at a coupler device in a quantum processor cell;

in response to the coupler control signal;

changing a coupler operating frequency of the coupler device toward a qubit operating frequency of a qubit device in the quantum processor cell; and

producing a phase shift in a quantum state of the qubit device by an interaction between the qubit device and the coupler device.

2. The quantum information control method of claim 1, comprising maintaining the coupler device in a ground state during the interaction.

3. The quantum information control method of claim 1, comprising, in response to the control signal, varying the coupler operating frequency over a time period of the interaction.

4. The quantum information control method of claim 3, comprising, in response to the control signal, maintaining the coupler operating frequency at a constant level during at least a portion of the time period.

5. The quantum information control method of claim 3, wherein the interaction produces a phase shift

6. The quantum information control method of claim 1, wherein the phase shift is controlled, at least in part, by a duration of the coupler control signal and an amplitude of the coupler control signal.

7. The quantum information control method of claim 1, wherein the coupler control signal comprises a bias signal that varies an offset electromagnetic field experienced by the coupler device.

8. The quantum information control method of claim 1, wherein the coupler device comprises a fluxonium qubit device and the qubit device comprises a transmon qubit device.

9. The quantum information control method of claim 1, wherein the interaction induces an energy level repulsion that gives rise to the phase shift.

10. The quantum information control method of claim 1, wherein the control signal comprises a direct current (DC) electrical signal.

11. A quantum computing system comprising:

a coupler device in a quantum processor cell;

a qubit device in the quantum processor cell; and

a control system communicably coupled to the quantum processor cell and operable to;

generate a coupler control signal configured to tune a coupler operating frequency of the coupler device toward a qubit operating frequency of the qubit device; and

communicate the coupler control signal to the coupler device to generate, between the qubit device and the coupler device, an interaction that produces a phase shift in a quantum state of the qubit device.

12. The quantum computing system of claim 11, wherein the control system is operable to maintain the coupler device in a ground state during the interaction.

13. The quantum computing system of claim 11, wherein the control system is operable to control the phase shift based, at least in part, on controlling a duration of the coupler control signal and an amplitude of the coupler control signal.

14. The quantum computing system of claim 11, wherein the coupler device comprises a fluxonium qubit device and the qubit device comprises a transmon qubit device.

15. The quantum computing system of claim 11, wherein the control signal is configured to produce, between the qubit device and the coupler device, an energy level repulsion that gives rise to the phase shift.

16. The quantum computing system of claim 11, wherein the control signal comprises a direct current (DC) electrical signal.

17. A quantum information control method for performing a quantum logic gate, the method comprising:

receiving coupler control signals at a coupler device in a quantum processor cell;

in response to the coupler control signals;

changing a coupler operating frequency of the coupler device toward a first qubit operating frequency of a first qubit device in the quantum processor cell; and

changing the coupler operating frequency away from the first qubit operation frequency and toward a second qubit operating frequency of a second qubit device in the quantum processor cell; and

producing a controlled-phase shift in a quantum state of the first and second qubit devices by interactions between the coupler device and respective the first and second qubit devices.

18. The quantum information control method of claim 17, comprising maintaining the coupler device in a ground state during the interactions.

19. The quantum information control method of claim 17, comprising, in response to the control signals, varying the coupler operating frequency over a time period of the first and second interactions.

20. The quantum information control method of claim 19, comprising, in response to the control signals, maintaining the coupler operating frequency at a constant level during at least a portion of the time period.

21. The quantum information control method of claim 19, wherein the interactions produces a controlled-phase shift

22. The quantum information control method of claim 17, wherein the controlled-phase shift is controlled, at least in part, by a duration of the coupler control signals and an amplitude of the coupler control signals.

23. The quantum information control method of claim 17, wherein the coupler device comprises a fluxonium qubit device and the first and second qubit devices comprise transmon qubit devices.

24. The quantum information control method of claim 17, wherein the interactions induce an energy level repulsion that gives rise to the controlled-phase shift.

25. The quantum information control method of claim 17, wherein the control signal comprises a direct current (DC) electrical signal.

26. A quantum computing system comprising:

a coupler device in a quantum processor cell;

a first qubit device in the quantum processor cell;

a second qubit device in the quantum processor cell; and

a control system communicably coupled to the quantum processor cell and operable to;

generate a first coupler control signal configured to tune a coupler operating frequency of the coupler device toward a first qubit operating frequency of the first qubit device;

generate a second coupler control signal configured to tune the coupler operating frequency away from the first qubit operating frequency and toward a second qubit operating frequency of the second qubit device; and

communicate the first and second coupler control signals to the coupler device to generate, between the first qubit device, the second qubit device and the coupler device, interactions that produce a controlled-phase shift in a quantum state of the first and second qubit devices.

27. The quantum computing system of claim 26, wherein the control system is operable to maintain the coupler device in a ground state during the interactions.

28. The quantum computing system of claim 26, wherein the controlled-phase shift is determined, at least in part, by durations of the respective first and second coupler control signals and amplitudes of the respective first and second coupler control signals.

29. The quantum computing system of claim 26, wherein the first and second coupler control signals comprise first and second bias signals that vary an offset electromagnetic field experienced by the coupler device.

30. The quantum computing system of claim 26, wherein the coupler device comprises a fluxonium qubit device and the first and second qubit devices comprises transmon qubit devices.

31. The quantum computing system of claim 26, wherein the control system is operable to generate first and second control signals to produce, between the coupler device and the respective first and second qubit devices, an energy level repulsion that gives rise to the controlled-phase shift.

32. The quantum computing system of claim 26, wherein the control signal comprises a direct current (DC) electrical signal.

33. A quantum information control method for performing a quantum logic gate, the method comprising:

receiving a coupler control signal at a coupler device in a quantum processor cell;

in response to the coupler control signal;

lowering a coupler operating frequency of the coupler device toward a frequency of a joint excited state of first and second qubit devices in the quantum processor cell; and

producing a controlled-phase shift in a quantum state of the first and second qubit devices by interactions between the coupler device and the respective first and second qubit devices.

34. The quantum information control method of claim 33, comprising maintaining the coupler device in a ground state during the interactions.

35. The quantum information control method of claim 33, comprising, in response to the control signal, varying the coupler operating frequency over a time period of the interactions.

36. The quantum information control method of claim 35, comprising, in response to the control signal, maintaining the coupler operating frequency at a constant level during at least a portion of the time period.

37. The quantum information control method of claim 33, wherein the controlled-phase shift is controlled, at least in part, by controlling a duration of the coupler control signal and an amplitude of the coupler control signal.

38. The quantum information control method of claim 33, wherein the coupler control signal comprises a bias signal that varies an offset electromagnetic field experienced by the coupler device.

39. The quantum information control method of claim 33, wherein the first and second qubit devices comprise transmon qubit devices.

40. The quantum information control method of claim 33, wherein the coupler device comprises a fluxonium qubit device, and the coupler operating frequency is maintained higher than frequencies of two-photon states of the respective first and second qubit devices during the interactions.

41. The quantum information control method of claim 33, wherein the interactions induce an energy level repulsion that gives rise to the controlled-phase shift.

42. The quantum information control method of claim 33, wherein the control signal comprises a direct current (DC) electrical signal.

43. A quantum computing system comprising:

a coupler device in a quantum processor cell;

a first qubit device in the quantum processor cell;

a second qubit device in the quantum processor cell; and

a control system communicably coupled to the quantum processor cell and operable to;

generate a coupler control signal that lowers a coupler operating frequency of the coupler device toward a frequency of a joint excited state of the first and second qubit devices; and

communicate the coupler control signal to the coupler device to generate, between the coupler device and the first and second qubit devices, an interaction that produces a controlled-phase shift in a quantum state of the first and second qubit devices.

44. The quantum computing system of claim 43, wherein the control system is operable to maintain the coupler device in a ground state during the interaction.

45. The quantum computing system of claim 43, wherein the control system is operable to control the controlled-phase shift based, at least in part, on controlling a duration of the coupler control signal and an amplitude of the coupler control signal.

46. The quantum computing system of claim 43, wherein the first and second qubit devices comprise transmon qubit devices.

47. The quantum computing system of claim 43, wherein the coupler device comprises a fluxonium qubit device, and the second coupler operating frequency is higher than frequencies of two-photon states of the respective first and second qubit devices.

48. The quantum computing system of claim 43, wherein the control signal comprises a direct current (DC) electrical signal.