Controlling a tunable floating coupler device in a superconducting quantum processing unit

Patent metadata

Field	Value
Publication number	US-12511567-B2
Application number	US-202217901633-A
Country	US
Kind code	B2
Filing date	Sep 1, 2022
Priority date	Mar 3, 2020
Publication date	Dec 30, 2025
Grant date	Dec 30, 2025

Abstract

In a general aspect, a superconducting quantum processing unit includes a first qubit device, a second qubit device, and a tunable floating coupler device coupled between the first and second qubit devices. Values of a coupling strength of the first and second qubit devices at a plurality of operating points of the tunable floating coupler device are measured. The operating points correspond to respective values of a magnetic flux applied to the tunable floating coupler device. Based on the measured values of the coupling strength, a parking value of the magnetic flux is identified. The parking value of the magnetic flux corresponds to a magnitude of the coupling strength being less than or equal to a threshold value; the threshold value is associated with a target gate fidelity for the superconducting quantum processing unit.

First claim

What is claimed is:

1 . A quantum computing system comprising:
a superconducting quantum processing unit comprising a first qubit device, a second qubit device, and a tunable floating coupler device coupled between the first and second qubit devices; and a control system communicably coupled to the superconducting quantum processing unit, the control system configured to perform operations comprising:
measuring values of a coupling strength of the first and second qubit devices at a plurality of operating points of the tunable floating coupler device, wherein the operating points correspond to respective values of a magnetic flux applied to the tunable floating coupler device; and
based on the measured values of the coupling strength, identifying a parking value of the magnetic flux applied to the tunable floating coupler device, wherein the parking value of the magnetic flux corresponds to a magnitude of the coupling strength being less than or equal to a threshold value associated with a target gate fidelity for the superconducting quantum processing unit.

2 . The quantum computing system of claim 1 , wherein the coupling strength comprises a first coupling strength of an XX coupling of the first and second qubit devices or a second coupling strength of a ZZ coupling of the first and second qubit devices.

3 . The quantum computing system of claim 1 , wherein:
the coupling strength (g) comprises a static coupling strength component (g 12 ) and an effective virtual coupling strength component (g eff ); and the effective virtual coupling strength component (g eff ), coupling strengths of the first or the second qubit devices and the tunable floating coupler device (g 1c and g 2c ), a transition frequency of the tunable floating coupler device (ω c ), and transition frequencies of the first and second qubit devices (ω j ), are related such that,

g
eff

=

g

1
⁢
c

⁢

g

2
⁢
c

2

⁢

∑

j
=
1

,
2

(

1

ω
c

-

ω
j

+

1

ω
c

+

ω
j

)

.

4 . The quantum computing system of claim 1 , wherein the parking value of the magnetic flux corresponds to the coupling strength being zero.

5 . The quantum computing system of claim 1 , wherein the coupling strength comprises a coupling strength of a ZZ coupling of the first and second qubit devices, and the threshold value is determined based on a gate time.

6 . The quantum computing system of claim 1 , wherein the coupling strength comprises a coupling strength of a ZZ coupling of the first and second qubit devices, and the threshold value is equal to

2

t
g

⁢

6
⁢

(

1
-
F

)

,

where F represents the target gate fidelity, and t g represents a gate time (t g ) of a single-qubit quantum logic gate associated with the target gate fidelity.

7 . The quantum computing system of claim 6 , wherein the target gate fidelity is 0.9999, and the threshold value is less than or equal to 260 kilohertz (kHz).

8 . The quantum computing system of claim 1 , wherein the tunable floating coupler device comprises two coupler electrodes that are electrically floating.

9 . The quantum computing system of claim 1 , wherein each of the first and second qubit devices comprises at least one qubit electrode, and a capacitance between the at least one qubit electrode of the first qubit device and the at least one qubit electrode of the second qubit device is equal to zero.

10 . The quantum computing system of claim 1 , wherein each of the first and second qubit devices comprises two qubit electrodes, and one of the two qubit electrodes is conductively connected to ground.

11 . The quantum computing system of claim 1 , wherein each of the first and second qubit devices comprises two qubit electrodes capacitively connected to ground.

12 . The quantum computing system of claim 1 , wherein the first qubit device comprises a first fixed-frequency qubit device, the second qubit device comprises a second fixed-frequency qubit device, and each of the values of the coupling strength are measured by a process comprising:
initializing the first fixed-frequency qubit device in one of a ground state or an excited state; and measuring a conditional phase accumulation of the second fixed-frequency qubit device.

13 . The quantum computing system of claim 1 , wherein the first qubit device comprises a first tunable qubit device, the second qubit device comprises a second tunable qubit device, and measuring the values of the coupling strength of the first and second qubit devices at the plurality of operating points of the tunable floating coupler device comprises:
tuning at least one of the first and second tunable qubit devices to bring the first and second tunable qubit devices into resonance with each other; and while the first and second tunable qubit devices are in resonance with each other, measuring the values of the coupling strength of the first and second tunable qubit devices at the plurality of operating points.

14 . The quantum computing system of

Assignees

• Rigetti & Co Llc

Inventors

• Sete Eyob A
• Poletto Stefano
• Manenti Riccardo
• Chen Angela Q
• Kulshreshtha Shobhan

Classifications

• G06N10/70

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

• G06N10/80

  Quantum programming, e.g. interfaces, languages or software-development kits for creating or handling programs capable of running on quantum computers; Platforms for simulating or accessing quantum computers, e.g. cloud-based quantum computing · CPC title

• G06N10/20

  Models of quantum computing, e.g. quantum circuits or universal quantum computers · CPC title

• H10N69/00

  Integrated devices, or assemblies of multiple devices, comprising at least one superconducting element covered by group H10N60/00 · CPC title

• B82Y10/00

  Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic · CPC title