Removing leakage in a quantum bit

Patent metadata

Field	Value
Publication number	US-10867258-B2
Application number	US-201916555672-A
Country	US
Kind code	B2
Filing date	Aug 29, 2019
Priority date	Oct 29, 2015
Publication date	Dec 15, 2020
Grant date	Dec 15, 2020

Abstract

Apparatus and methods for removing leakage from a qubit. In one aspect, an apparatus includes one or more qubits, wherein each qubit facilitates occupation of at least one of a plurality of qubit levels, the qubit levels including two computational levels and one or more non-computational levels that are each higher than the computational levels, wherein the qubit facilitates transitions between qubit levels associated with a corresponding transition frequency; a cavity, wherein the cavity defines a cavity frequency; one or more couplers coupling each qubit to the cavity; one or more couplers coupling the cavity to an environment external to the one or more qubits and the cavity; a frequency controller that controls the frequency of each qubit such that, for each qubit, the frequency of the qubit is adjusted relative to the cavity frequency such that a population of a non-computational level is transferred to the cavity.

First claim

What is claimed is:

1. An apparatus, comprising:
one or more qubits, wherein each qubit facilitates occupation of at least one of a plurality of qubit levels, the qubit levels including two computational qubit levels and one or more non-computational qubit levels that are each higher than the computational qubit levels, and wherein the qubit facilitates transitions between qubit levels associated with a corresponding transition frequency;
a cavity, wherein the cavity defines a cavity frequency;
one or more couplers coupling each qubit to the cavity; and
one or more couplers coupling the cavity to an environment external to the one or more qubits and the cavity;
a frequency controller that controls the frequency of qubits, wherein for each qubit that the frequency controller controls, the frequency controller is configured to sweep the qubit frequency past the cavity frequency such that a population of a non-computational level is transferred to the cavity.

2. The apparatus of claim 1 , where sweeping the qubit frequency comprises:
determining a qubit frequency trajectory relative to the cavity frequency; and
adjusting the qubit frequency according to the qubit frequency trajectory to cause the qubit transition frequencies to sequentially become aligned with the cavity frequency for population transfer to the cavity.

3. The apparatus of claim 1 , wherein the environment is formed by a wire, which connects to a load, optionally wherein the wire comprises a readout line.

4. The apparatus of claim 1 , wherein the cavity comprises a readout resonator.

5. The apparatus of claim 1 , wherein the one or more qubits exhibit weak non-linearity.

6. A method, comprising:
accessing a quantum system that comprises:
one or more qubits, wherein each qubit facilitates occupation of at least one of a plurality of qubit levels, the qubit levels including two computational qubit levels and one or more non-computational qubit levels that are each higher than the computational qubit levels, and wherein the qubit facilitates transitions between qubit levels associated with a corresponding transition frequency;
a cavity, wherein the cavity defines a cavity frequency;
one or more couplers coupling each qubit to the cavity; and
one or more couplers coupling the cavity to an environment external to the one or more qubits and the cavity;
a frequency controller that controls the frequency of qubits, wherein for each qubit that the frequency controller controls, the frequency controller is configured to sweep the qubit frequency past the cavity frequency such that a population of a non-computational level is transferred to the cavity; and

controlling the frequency of each qubit such that, for each qubit, the frequency of the qubit is swept past the cavity frequency such that a population of a non-computational level is transferred to the cavity.

7. The method of claim 6 , wherein sweeping the qubit frequency comprises:
determining a qubit frequency trajectory relative to the cavity frequency; and
adjusting the qubit frequency according to the qubit frequency trajectory to cause the qubit transition frequencies to sequentially become aligned with the cavity frequency for population transfer to the cavity.

8. The method of claim 6 , wherein the quantum system is provided for use in a quantum computation.

9. The method of claim 8 , wherein the method of claim 6 is repeatedly performed after one or more computation operations in the quantum computation.

10. The method of claim 8 , wherein a final step of the one or more computation operation comprises a measurement operation.

11. The method of claim 8 , wherein the method is repeatedly performed immediately before a measurement operation associated with one or more computation operations in the quantum computation.

12. The method of claim 6 , wherein prior knowledge of a population of each of the qubit states is not needed.

13. A method, comprising:
in response to performing a computation in a quantum system that comprises:
one or more qubits, wherein each qubit facilitates occupation of at least one of a plurality of qubit levels, the qubit levels including two computational qubit levels and one or more non-computational qubit levels that are each higher than the computational qubit levels, and wherein the qubit facilitates transitions between qubit levels associated with a corresponding transition frequency;
a cavity, wherein the cavity defines a cavity frequency; and
a frequency controller that controls the frequency of qubits, wherein for each qubit that the frequency controller controls, to the frequency controller is configured to sweep the qubit frequency past the cavity frequency such that a population of a non-computational level is transferred to the cavity;

controlling the frequency of each qubit that the frequency controller controls without prior knowledge of the population of the qubit levels such that, for each qubit that the frequency controller controls, the frequency of the qubit is adjusted relative to the cavity frequency such that a population of the non-computational level is transferred to the cavity.

14. The method of claim 13 , wherein sweeping the qubit frequency comprises:
determining a qubit frequency trajectory relative to the cavity frequency; and
adjusting the qubit frequency according to the qubit frequency trajectory to cause the qubit transition frequencies to sequentially become aligned with the cavity frequency for population transfer to the cavity.

Assignees

• Google Llc

Inventors

• Barends Rami

Classifications

• G06N10/70

  Quantum error correction, detection or prevention, e.g. surface codes or magic state distillation · CPC title

• G06N10/40 Primary

  Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control · CPC title

• F41J9/02

  Land-based targets {, e.g. inflatable targets supported by fluid pressure} · CPC title

• F41J5/18

  Targets having hit-indicating means actuated or moved mechanically when the target has been hit, e.g. discs or flags (the target as a whole disappearing or moving when hit F41J7/04) · CPC title

• A63F9/0204

  Targets therefor (for ball games A63B63/00) · CPC title