Capacitively-shunted asymmetric DC-SQUID for qubit readout and reset

Patent metadata

Field	Value
Publication number	US-11367012-B2
Application number	US-202017128984-A
Country	US
Kind code	B2
Filing date	Dec 21, 2020
Priority date	Oct 19, 2017
Publication date	Jun 21, 2022
Grant date	Jun 21, 2022

Abstract

A tunable resonator is formed by shunting a set of asymmetric DC-SQUIDs with a capacitive device. An asymmetric DC-SQUID includes a first Josephson junction and a second Josephson junction, where the critical currents of the first and second Josephson junctions are different. A coupling is formed between the tunable resonator and a qubit such that the capacitively-shunted asymmetric DC-SQUIDs can dispersively read a quantum state of the qubit. An external magnetic flux is set to a first value and applied to the tunable resonator. A first value of the external magnetic flux causes the tunable resonator to tune to a first frequency within a first frequency difference from a resonance frequency of the qubit, the tunable resonator tuning to the first frequency causes active reset of the qubit.

First claim

What is claimed is:

1. A superconducting device comprising:
a capacitive device shunting at least one asymmetric direct current superconducting quantum interference device (DC-SQUID); and
a tunable resonator formed by the at least one asymmetric DC-SQUID and the capacitive device, the tunable resonator being responsive to an external magnetic flux such that a first value of the external magnetic flux causes the tunable resonator to tune to a first frequency, and such that tuning to the first frequency causes active reset of a qubit coupled to the tunable resonator, and
wherein the first frequency being within a first frequency difference from the resonance frequency of the qubit causes the qubit to release a photon, the releasing causing the qubit to relax to a ground energy state.

2. The superconducting device of claim 1 ,
wherein the tunable resonator is further responsive to the external magnetic flux such that a second value of the external magnetic flux causes the tunable resonator to tune to a second frequency, wherein the first frequency is within a first frequency difference from a resonance frequency of the qubit,
wherein the second frequency is detuned from the resonance frequency of the qubit by at least a second frequency difference, and
wherein the tunable resonator tuning to the second frequency enables a dispersive readout operation of a quantum state of the qubit to be performed.

3. The superconducting device of claim 2 , wherein the second frequency is a maximum frequency in a frequency resonance range of the tunable resonator.

4. The superconducting device of claim 2 , wherein the second frequency difference is a function of a degree of asymmetry between a first Josephson junction and a second Josephson junction in the at least one asymmetric DC-SQUID.

5. The superconducting device of claim 1 , wherein the first frequency difference is zero and the first frequency is the resonance frequency of the qubit.

6. The superconducting device of claim 1 , wherein forcing the qubit to the ground energy state is faster than an energy decay time constant of the qubit.

7. The superconducting device of claim 1 , wherein the at least one asymmetric DC-SQUID includes only one asymmetric DC-SQUID.

8. The superconducting device of claim 1 , further comprising:
wherein the at least one asymmetric DC-SQUID includes a plurality of asymmetric DC-SQUIDs; and
wherein the superconducting device further comprises a series connection connecting the plurality of asymmetric DC-SQUIDs.

9. The superconducting device of claim 8 , wherein the series connection comprises a superconducting wire.

10. The superconducting device of claim 1 , further comprising:
a first pad formed on a first side of the at least one asymmetric DC-SQUID; and
a second pad formed on a second side of the at least one asymmetric DC-SQUID, wherein the first pad and the second pad are separated by a distance, and wherein the first pad and the second pad together form the capacitive device.

11. A method comprising:
forming a tunable resonator by shunting at least one asymmetric direct current superconducting quantum interference device (DC-SQUID) with a capacitive device; and
actively resetting a qubit by applying an external magnetic flux of a first value to the tunable resonator, wherein a first value of the external magnetic flux causes the tunable resonator to tune to a first frequency,
wherein the first frequency being within a first frequency difference from the resonance frequency of the qubit causes the qubit to release a photon, the releasing causing the qubit to relax to a ground energy state.

12. The method of claim 11 , further comprising:
changing the external magnetic flux to a second value, wherein the second value of the external magnetic flux causes the tunable resonator to tune to a second frequency, wherein the first frequency is within a first frequency difference from a resonance frequency of the qubit, wherein the second frequency is detuned from the resonance frequency of the qubit by at least a second frequency difference; and
performing, using the tunable resonator tuned to the second frequency, a dispersive readout operation of a quantum state of the qubit.

13. The method of claim 12 , wherein the second frequency is a maximum frequency in a frequency resonance range of the tunable resonator.

14. The method of claim 12 , wherein the second frequency difference is a function of a degree of asymmetry between a first Josephson junction and a second Josephson junction in the at least one asymmetric DC-SQUID.

15. The method of claim 11 , wherein the first frequency difference is zero and the first frequency is the resonance frequency of the qubit.

16. The method of claim 11 , wherein forcing the qubit to the ground energy state is faster than an energy decay time constant T 1 of the qubit.

17. The method of claim 11 , wherein the at least one asymmetric DC-SQUID includes only one asymmetric DC-SQUID.

18. The method of claim 11 , further comprising:
wherein the at least one asymmetric DC-SQUID includes a plurality of asymmetric DC-SQUIDs; and
wherein the method further comprises connecting the plurality of asymmetric DC-SQUIDs in a series.

19. The method of claim 18 , wherein the plurality of asymmetric DC-SQUIDs are connected in series using a superconductor.

20. The method of claim 11 , further comprising:
forming a first pad on a first side of the at least one asymmetric DC-SQUID; and
forming a second pad on a second side of the at least one asymmetric DC-SQUID, wherein the first pad and the second pad are separated by a distance, and wherein the first pad and the second pad together form the capacitive device.

21. A superconducting fabrication system which when operated to fabricate a tunable resonator device performing operations comprising:
forming the tunable resonator by shunting at least one asymmetric direct current superconducting quantum interference device (DC-SQUID) with a capacitive device; and
actively resetting a qubit by applying an external magnetic flux of a first value to the tunable resonator, wherein a first value of the external magnetic flux causes the tunable resonator to tune to a first frequency,
wherein the first frequency being within a first frequency difference from the resonance frequency of the qubit causes the qubit to release a photon, the releasing causing the qubit to relax to a ground energy state.

22. The superconducting fabrication system of claim 21 ,
wherein the tunable resonator is further responsive to the external magnetic flux such that a second value of the external magnetic flux causes the tunable resonator to tune to a second frequency,
wherein the first frequency is within a first frequency difference from a resonance frequency of the qubit,
wherein the second frequency is detuned from the resonance frequency of the qubit by at least a second frequency difference; and
wherein the tunable resonator tuning to the second frequency enables a dispersive readout operation of a quantum state of the qubit.

23. The superconducting fabrication system of claim 22 , wherein the second frequency is a maximum frequency in a frequency resonance range of the tunable resonator.

Assignees

• IBM

Inventors

• Abdo Baleegh

Classifications

• G06N10/40

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

• H03K17/92 Primary

  by the use, as active elements, of superconductive devices · CPC title

• H03K19/195

  using superconductive devices · CPC title

• G06N10/00 Primary

  Quantum computing, i.e. information processing based on quantum-mechanical phenomena · CPC title

• H01L39/2493

  Electricity · mapped topic