IP Library › Granted Patent US 12,632,761
Granted Patent B2
US 12,632,761 · App. 17/836,268 · Granted May 19, 2026

Controlling interaction between coupled superconducting quantum bits

Inventors: Aaron Finck (White Plains, NY); Cihan Kurter (White Plains, NY); Sarunya Bangsaruntip (Mount Kisco, NY); Harry Jonathon Mamin (Palo Alto, CA); Charles Thomas Rettner (San Jose, CA); John Blair (Katonah, NY); George Andrew Keefe (Cortlandt Manor, NY)
Assignee: International Business Machines Corporation
G06N10/40G06N10/20H10N60/805H10N60/84
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Quick Facts
Patent No.
US 12,632,761
App. No.
17/836,268
Granted
May 19, 2026
Kind
B2
Abstract

A device comprises a first superconducting quantum bit, a second superconducting quantum bit, and a coupler circuit. The first superconducting quantum bit comprises a superconducting tunnel junction and a shunt inductor which form a first superconducting loop. The second superconducting quantum bit comprises a superconducting tunnel junction and a shunt inductor which form a second superconducting loop. The coupler circuit is coupled between the first and second superconducting quantum bits. The coupler circuit is configured to implement an entanglement gate operation between the first and second superconducting quantum bits through exchange interactions between the coupler circuit and the first superconducting quantum bit and the second superconducting quantum bit, when the coupler circuit is driven by a control signal. The coupler circuit is configured to suppress interaction between the first superconducting quantum bit and the second superconducting quantum bit, when the coupler circuit is not driven by the control signal.

Claims (63)

1 . A device, comprising:

a first superconducting quantum bit comprising a superconducting tunnel junction and a shunt inductor which form a first superconducting loop;

a second superconducting quantum bit comprising a superconducting tunnel junction and a shunt inductor which form a second superconducting loop; and

a coupler circuit which comprises a capacitor and an inductive element coupled in parallel between a first node and a second node, with the first superconducting quantum bit coupled to the first node and the second superconducting quantum bit coupled to the second node;

wherein the coupler circuit is configured to implement an entanglement gate operation between the first superconducting quantum bit and the second superconducting quantum bit through exchange interactions between the coupler circuit and the first superconducting quantum bit and the second superconducting quantum bit, when the coupler circuit is driven by a microwave control signal having a frequency which corresponds to an operating frequency of the coupler circuit; and

wherein the coupler circuit is configured to suppress interaction between the first superconducting quantum bit and the second superconducting quantum bit, when the coupler circuit is not driven by the microwave control signal.

2 . The device of claim 1 , wherein the first superconducting quantum bit and the second superconducting quantum bit each comprise a superconducting fluxonium quantum bit.

3 . The device of claim 1 , further comprising a drive control line, which is one of capacitively and inductively coupled to the coupler circuit, and configured to apply the microwave control signal to the coupler circuit.

4 . The device of claim 1 , wherein:

the coupler circuit comprises a superconducting resonator circuit; and

the inductive element comprises a superconducting inductor coupled in parallel with the capacitor between the first node and the second node of the coupler circuit.

5 . The device of claim 1 , wherein:

the coupler circuit comprises a third superconducting quantum bit; and

the inductive element comprises a superconducting tunnel junction coupled in parallel with the capacitor between the first node and the second node of the coupler circuit.

6 . The device of claim 5 , wherein the third superconducting quantum bit comprises a superconducting transmon quantum bit.

7 . The device of claim 5 , wherein the superconducting tunnel junction comprises a Josephson junction.

8 . The device of claim 5 , wherein:

the first superconducting quantum bit is configured to have a first transition frequency;

the second superconducting quantum bit is configured to have a second transition frequency; and

the third superconducting quantum bit comprises a third transition frequency, which is detuned from, and greater than, the first transition frequency and the second transition frequency.

9 . The device of claim 1 , further comprising:

a first flux bias control line coupled to the first superconducting loop, and configured to apply a first flux bias control signal to adjust a transition frequency of the first superconducting quantum bit; and

a second flux bias control line coupled to the second superconducting loop, and configured to apply a second flux bias control signal to adjust a transition frequency of the second superconducting quantum bit;

wherein the entanglement gate operation is implemented by the first flux bias control signal applying about one-half magnetic flux quantum to the first superconducting loop of the first superconducting quantum bit, and the second flux bias control signal applying about one-half magnetic flux quantum to the second superconducting loop of the second superconducting quantum bit.

10 . A system, comprising;

a quantum processor comprising an array of superconducting quantum bits; and

a control system configured to generate control signals to control the quantum processor;

wherein the array of superconducting quantum bits comprises:

a first superconducting quantum bit comprising a superconducting tunnel junction and a shunt inductor which form a first superconducting loop;

a second superconducting quantum bit comprising a superconducting tunnel junction and a shunt inductor which form a second superconducting loop; and

a coupler circuit which comprises a capacitor and an inductive element coupled in parallel between a first node and a second node, with the first superconducting quantum bit coupled to the first node and the second superconducting quantum bit coupled to the second node;

wherein the coupler circuit is configured to implement an entanglement gate operation between the first superconducting quantum bit and the second superconducting quantum bit through exchange interactions between the coupler circuit and the first superconducting quantum bit and the second superconducting quantum bit, when the coupler circuit is driven by a microwave control signal that is generated by the control system, the microwave control signal having a frequency which corresponds to an operating frequency of the coupler circuit; and

wherein the coupler circuit is configured to suppress interaction between the first superconducting quantum bit and the second superconducting quantum bit, when the coupler circuit is not driven by the microwave control signal.

11 . The system of claim 10 , wherein the first superconducting quantum bit and the second superconducting quantum bit each comprise a superconducting fluxonium quantum bit.

12 . The system of claim 10 , wherein:

the coupler circuit comprises a superconducting resonator circuit; and

the inductive element comprises a superconducting inductor coupled in parallel with the capacitor between the first node and the second node of the coupler circuit.

13 . The system of claim 10 , wherein:

the coupler circuit comprises a third superconducting quantum bit; and

the inductive element comprises a superconducting tunnel junction coupled in parallel with the capacitor between the first node and the second node of the coupler circuit.

14 . The system of claim 13 , wherein the third superconducting quantum bit comprises a superconducting transmon quantum bit.

15 . The system of claim 13 , wherein: the superconducting tunnel junction comprises a Josephson junction.

16 . The system of claim 10 , wherein the quantum processor further comprises:

a first flux bias control line coupled to the first superconducting loop, and configured to apply a first flux bias control signal to adjust a transition frequency of the first superconducting quantum bit; and

a second flux bias control line coupled to the second superconducting loop, and configured to applying a second flux bias control signal to adjust a transition frequency of the second superconducting quantum bit;

wherein the entanglement gate operation is implemented by the control system generating the first flux bias control signal to apply about one-half magnetic flux quantum to the first superconducting loop of the first superconducting quantum bit, and generating the second flux bias control signal to apply about one-half magnetic flux quantum to the second superconducting loop of the second superconducting quantum bit.

17 . A device comprising a first superconducting fluxonium quantum bit and a second superconducting fluxonium quantum bit coupled by a coupler circuit which is driven by a microwave control signal having a frequency which corresponds to an operating frequency of the coupler circuit, to control an interaction between the first superconducting fluxonium quantum bit and the second superconducting fluxonium quantum bit, wherein:

the coupler circuit comprises a superconducting resonator circuit comprising a superconducting inductor and a capacitor coupled in parallel between a first node and a second node of the coupler circuit;

the first superconducting fluxonium quantum bit is coupled to the first node of the coupler circuit; and

the second superconducting fluxonium quantum bit is coupled to the second node of the coupler circuit.

18 . A device comprising a first superconducting fluxonium quantum bit and a second superconducting fluxonium quantum bit coupled by a coupler circuit which is driven by a microwave control signal having a frequency which corresponds to an operating frequency of the coupler circuit, to control an interaction between the first superconducting fluxonium quantum bit and the second superconducting fluxonium quantum bit, wherein:

the coupler circuit comprises a superconducting quantum bit comprising a superconducting tunnel junction and a capacitor coupled in parallel between a first node and a second node of the coupler circuit;

the superconducting quantum bit is configured as a coupling bus between the first superconducting fluxonium quantum bit and the second superconducting fluxonium quantum bit;

the first superconducting fluxonium quantum bit is coupled to the first node of the coupler circuit; and

the second superconducting fluxonium quantum bit is coupled to the second node of the coupler circuit.

19 . The device of claim 17 , further comprising:

a first flux bias control line coupled to the first superconducting fluxonium quantum bit, and configured to apply a first flux bias control signal to adjust a transition frequency of the first superconducting fluxonium quantum bit; and

a second flux bias control line coupled to the second superconducting fluxonium quantum bit, and configured to apply a second flux bias control signal to adjust a transition frequency of the second superconducting fluxonium quantum bit;

wherein an entanglement gate operation is implemented by the first flux bias control signal applying about one-half magnetic flux quantum to the first superconducting fluxonium quantum bit, the second flux bias control signal applying about one-half magnetic flux quantum to the second superconducting fluxonium quantum bit, and driving the coupler circuit with the microwave control signal.

20 . The device of claim 18 , further comprising:

a first flux bias control line coupled to the first superconducting fluxonium quantum bit, and configured to apply a first flux bias control signal to adjust a transition frequency of the first superconducting fluxonium quantum bit; and

a second flux bias control line coupled to the second superconducting fluxonium quantum bit, and configured to apply a second flux bias control signal to adjust a transition frequency of the second superconducting fluxonium quantum bit;

wherein an entanglement gate operation is implemented by the first flux bias control signal applying about one-half magnetic flux quantum to the first superconducting fluxonium quantum bit, the second flux bias control signal applying about one-half magnetic flux quantum to the second superconducting fluxonium quantum bit, and driving the coupler circuit with the microwave control signal.

Assignments (1)
ASSIGNMENT OF ASSIGNOR'S INTEREST Recorded Jun 9, 2022
From: FINCK, AARON; KURTER, CIHAN; BANGSARUNTIP, SARUNYA; MAMIN, HARRY JONATHON; RETTNER, CHARLES THOMAS; BLAIR, JOHN; KEEFE, GEORGE ANDREW
To: INTERNATIONAL BUSINESS MACHINES CORPORATION
Reel/Frame 060149/0640 →
Continuity (1)
Related Publication 20230401476A1 · Dec 14, 2023
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