Method and Circuit for Implementing Two-Qubit Gate

1 . A method for implementing a two-qubit gate, comprising:

applying a coupling control signal to an adjustable coupler, wherein the adjustable coupler is a coupler between a first data qubit and a second data qubit; and

activating, by means of adjusting the coupling control signal, longitudinal coupling between the first data qubit and the second data qubit within a predetermined time, so as to implement the two-qubit gate.

2 . The method as claimed in claim 1 , wherein the activating, by means of adjusting the coupling control signal, longitudinal coupling between the first data qubit and the second data qubit within a predetermined time, so as to implement the two-qubit gate comprises:

activating, by means of adjusting the coupling control signal, the longitudinal coupling between the first data qubit and the second data qubit within the predetermined time, and controlling other coupling between the first data qubit and the second data qubit to be minimum, so as to implement the two-qubit gate, wherein the other coupling is coupling other than the longitudinal coupling.

3 . The method as claimed in claim 42 , wherein the activating, by means of adjusting the coupling control signal, the longitudinal coupling between the first data qubit and the second data qubit within the predetermined time, and controlling other coupling between the first data qubit and the second data qubit to be minimum comprises:

determining a target adjustment parameter of the coupling control signal, wherein the target adjustment parameter comprises at least one of the following: an amplitude of the coupling control signal and a period of the coupling control signal;

obtaining an adjusted coupling control signal by means of adjusting the target adjustment parameter of the coupling control signal; and

activating, by means of applying the adjusted coupling control signal to the adjustable coupler, the longitudinal coupling between the first data qubit and the second data qubit within the predetermined time, and controlling the other coupling between the first data qubit and the second data qubit to be minimum.

4 . The method as claimed in claim 3 , wherein the determining a target adjustment parameter of the coupling control signal comprises:

determining multiple coupling items comprised in the other coupling;

respectively determining candidate adjustment parameters corresponding to the coupling control signal when the multiple coupling items are minimal; and

determining, based on a predetermined optimization method and the candidate adjustment parameters, the target adjustment parameter of the coupling control signal when the multiple coupling items are simultaneously minimal.

5 . The method as claimed in claim 1 , wherein the first data qubit is a first Fluxonium qubit, and the second data qubit is a second Fluxonium qubit.

6 . A circuit for implementing a two-qubit gate, comprising: a first data qubit, a second data qubit, an adjustable coupler between the first data qubit and the second data qubit, a signal generator, and a signal controller, wherein,

the signal generator is configured to generate a coupling control signal and apply the coupling control signal to the adjustable coupler; and

the signal controller is configured to activate, by means of controlling the signal generator to adjust the coupling control signal, longitudinal coupling between the first data qubit and the second data qubit within a predetermined time, so as to implement the two-qubit gate.

7 . The circuit as claimed in claim 6 , wherein the signal controller comprises: a scanner and an adjuster, wherein,

the scanner is configured to scan other coupling between the first data qubit and the second data qubit to obtain other coupling results, wherein the other coupling is coupling other than the longitudinal coupling; and

the adjuster is configured to activate, by means of adjusting the coupling control signal based on the other coupling results, the longitudinal coupling between the first data qubit and the second data qubit within the predetermined time, and control other coupling between the first data qubit and the second data qubit to be minimum, so as to implement the two-qubit gate.

8 . The circuit as claimed in claim 6 , wherein the first data qubit is a first Fluxonium qubit, and the second data qubit is a second Fluxonium qubit.

9 . The circuit as claimed in claim 8 , wherein a structure formed by a first Fluxonium qubit, a second Fluxonium qubit, and the adjustable coupler comprises: a single-loop inductively coupled Fluxonium structure, wherein the adjustable coupler in the single-loop inductively coupled Fluxonium structure is a third Fluxonium qubit.

10 . The circuit as claimed in claim 9 , wherein, in the single-loop inductively coupled Fluxonium structure,

an inductance of the first Fluxonium qubit is an inductance obtained by connecting a first inductor and a second inductor in series;

an inductance of the second Fluxonium qubit is an inductance obtained by connecting a third inductor and a fourth inductor in series; and

an inductance of the third Fluxonium qubit is an inductance obtained by connecting the second inductor, a fifth inductor, and the fourth inductor in series.

11 . The circuit as claimed in claim 8 , wherein a structure formed by the first Fluxonium qubit, the second Fluxonium qubit, and the adjustable coupler comprises: a grounded double-loop Superconducting Quantum Interference Device (SQUID) structure, wherein the adjustable coupler in the grounded double-loop SQUID structure comprises a first grounded loop and a second grounded loop.

12 . The circuit as claimed in claim 11 , wherein, in the grounded dual-loop SQUID structure,

an inductance of the first Fluxonium qubit is an inductance obtained by connecting a first inductor and a second inductor in series, wherein one end of the second inductor is connected to the first inductor while the other end thereof is grounded;

an inductance of the second Fluxonium qubit is an inductance obtained by connecting a third inductor and a fourth inductor in series, wherein one end of the fourth inductor is connected to the third inductor while the other end thereof is grounded;

the first grounded loop is obtained by connecting a fifth inductor, the second inductor, and a Josephson junction in series, and one end of the Josephson junction is connected to the fifth inductor while the other end thereof is grounded; and

the second grounded loop is obtained by connecting a sixth inductor, the fourth inductor, and the Josephson junction in series, and the Josephson junction is connected to one end of the fifth inductor and the sixth inductor while the other end thereof is grounded.

13 . The circuit as claimed in claim 8 , wherein a structure formed by the first Fluxonium qubit, the second Fluxonium qubit, and the adjustable coupler comprises: a suspended single-loop SQUID structure, wherein the adjustable coupler in the suspended single-loop SQUID structure is a single-loop SQUID.

14 . The circuit as claimed in claim 13 , wherein, in the grounded dual-loop SQUID structure,

an inductance of the first Fluxonium qubit is an inductance obtained by connecting a first inductor and a second inductor in series;

an inductance of the second Fluxonium qubit is an inductance obtained by connecting a third inductor and a fourth inductor in series; and

an inductance of the single-loop SQUID is an inductance obtained by connecting the second inductor and the fourth inductor in series.