Encoding two-qubit interactions

Patent metadata

Field	Value
Publication number	US-9940586-B1
Application number	US-201715659061-A
Country	US
Kind code	B1
Filing date	Jul 25, 2017
Priority date	Jul 25, 2017
Publication date	Apr 10, 2018
Grant date	Apr 10, 2018

Abstract

Systems and methods are provided for encoding two-qubit interactions. A quantum circuit comprises first and second logical qubits, each comprising a Bacon-Shor code block. A first edge of each logical qubit contains physical qubits each coupled to at least one neighboring physical qubit along the first edge along a first axis of the Bloch sphere and a second edge of each logical qubit contains physical qubits each coupled to at least one neighboring physical qubit along the second edge along a second axis of the Bloch sphere. A set of couplers couple the first and second logical qubits along the first axis of the Bloch sphere, with each of the set of couplers coupling a physical qubit along the second edge of the first logical qubit to a corresponding physical qubit along the second edge of the second logical qubit along the first axis of the Bloch sphere.

First claim

What is claimed is:

1. A quantum circuit comprising:
first and second logical qubits, each comprising a Bacon-Shor code block comprising a plurality of physical qubits coupled in an array, such that a first edge of each logical qubit contains physical qubits each coupled to at least one neighboring physical qubit along the first edge along a first axis of the Bloch sphere and a second edge of each logical qubit contains physical qubits each coupled to at least one neighboring physical qubit along the second edge along a second axis of the Bloch sphere; and
a set of couplers that couple the first and second logical qubits along the first axis of the Bloch sphere, each of the set of couplers coupling a physical qubit along the second edge of the first logical qubit to a corresponding physical qubit along the second edge of the second logical qubit along the first axis of the Bloch sphere.

2. The quantum circuit of claim 1 , wherein the set of couplers is a first set of couplers, the quantum circuit further comprising:
a third logical qubit comprising a Bacon-Shor code block comprising a plurality of physical qubits coupled in an array, such that a first edge of the third logical qubit contains physical qubits each coupled to at least one neighboring physical qubit along the first edge along the first axis of the Bloch sphere and a second edge of the third logical qubit contains physical qubits each coupled to at least one neighboring physical qubit along the second edge along the second axis of the Bloch sphere; and
a second set of couplers that couple the first and third logical qubits along the second axis of the Bloch sphere, each of the second set of couplers coupling a physical qubit along the first edge of the first logical qubit to a corresponding physical qubit along the first edge of the third logical qubit along the second axis of the Bloch sphere.

3. The quantum circuit of claim 1 , wherein the first axis of the Bloch sphere is the X-axis and the second axis of the Bloch sphere is the Z-axis.

4. The quantum circuit of claim 1 , wherein each of the set of couplers is tunable via a classical control, such that a strength of the coupling the first and second logical qubits along the first axis of the Bloch sphere is tunable.

5. The quantum circuit of claim 4 , wherein a given classical control applies a flux to its associated coupler.

6. The quantum circuit of claim 1 , wherein the set of couplers is a first set of couplers, the quantum circuit further comprising:
a third logical qubit comprising a Bacon-Shor code block comprising a plurality of physical qubits coupled in an array, such that a first edge of the third logical qubit contains physical qubits each coupled to at least one neighboring physical qubit along the first edge along the first axis of the Bloch sphere and a second edge of the third logical qubit contains physical qubits each coupled to at least one neighboring physical qubit along the second edge along the second axis of the Bloch sphere; and
a second set of couplers that couple the first and third logical qubits along the first axis of the Bloch sphere, each of the second set of couplers coupling a physical qubit along the second edge of the first logical qubit to a corresponding physical qubit along the second edge of the third logical qubit along the first axis of the Bloch sphere.

7. The quantum circuit of claim 6 further comprising:
a fourth logical qubit comprising a Bacon-Shor code block comprising a plurality of physical qubits coupled in an array, such that a first edge of the fourth logical qubit contains physical qubits each coupled to at least one neighboring physical qubit along the first edge along the first axis of the Bloch sphere and a second edge of the fourth logical qubit contains physical qubits each coupled to at least one neighboring physical qubit along the second edge along the second axis of the Bloch sphere; and
a third set of couplers that couple the second and fourth logical qubits along the first axis of the Bloch sphere, each of the second set of couplers coupling a physical qubit along the second edge of the second logical qubit to a corresponding physical qubit along the second edge of the fourth logical qubit along the first axis of the Bloch sphere.

8. The quantum circuit of claim 1 , wherein the first axis of the Bloch sphere is the X-axis and the second axis of the Bloch sphere is the Y-axis.

9. A method for constructing a quantum circuit comprising:
fabricating a first logical qubit as a first Bacon-Shor code block, the first logical qubit comprising at least a first physical qubit, a second physical qubit coupled to the first physical qubit along a first axis of the Bloch sphere, and a third physical qubit coupled to the first physical qubit along a second axis of the Bloch sphere;
fabricating a second logical qubit as a second Bacon-Shor code block, the second logical qubit comprising at least a fourth physical qubit, a fifth physical qubit coupled to the fourth physical qubit along the first axis of the Bloch sphere, and a sixth physical qubit coupled to the fourth physical qubit along the second axis of the Bloch sphere;
coupling the first physical qubit to the fourth physical qubit along the first axis of the Bloch sphere with a first coupler; and
coupling the third physical qubit to the sixth physical qubit along the first axis of the Bloch sphere with a second coupler.

10. The method of claim 9 , further comprising:
fabricating a third logical qubit as a third Bacon-Shor code block, the third logical qubit comprising at least a seventh physical qubit, an eighth physical qubit coupled to the seventh physical qubit along the first axis of the Bloch sphere, and a ninth physical qubit coupled to the seventh physical qubit along the second axis of the Bloch sphere;
coupling the first physical qubit to the seventh physical qubit along the second axis of the Bloch sphere with a third coupler; and
coupling the second physical qubit to the eighth physical qubit along the second axis of the Bloch sphere with a fourth coupler.

11. The method of claim 10 , further comprising:
fabricating a fourth logical qubit as a fourth Bacon-Shor code block, the fourth logical qubit comprising at least a tenth physical qubit, an eleventh physical qubit coupled to the tenth physical qubit along the first axis of the Bloch sphere, and a twelfth physical qubit coupled to the tenth physical qubit along the second axis of the Bloch sphere;
coupling the tenth physical qubit to the seventh physical qubit along the first axis of the Bloch sphere with a fifth coupler; and
coupling the twelfth physical qubit to the ninth physical qubit along the first axis of the Bloch sphere with a sixth coupler.

12. The method of claim 11 , wherein the first axis of the Bloch sphere is the Y-axis and the second axis of the Bloch sphere is the X-axis.

13. The method of claim 9 , the first coupler having a first coupling strength and the second coupler having a second coupling strength and the method further comprising:
tuning the first coupling strength via a first classical control; and
tuning the second coupling strength via a second classical control, the tuning of each of the first coupling strength and the second coupling strength being coordinated such that a strength of the coupling the first and second logical qubits along the first axis of the Bloch sphere is tunable.

14. The method of claim 13 , wherein the first classical control applies a flux to the first coupler, and second classical control applies a flux to the second coupler.

15. The method of claim 9 , further co

Assignees

• Epstein Ryan J
• Ferguson David George
• Northrop Grumman Systems Corp

Inventors

• Epstein Ryan J
• Ferguson David George

Classifications

• H03K19/195

  using superconductive devices · CPC title

• H01L39/223

  Electricity · mapped topic

• G06N99/002 Primary

  Physics · mapped topic

• G06N10/20

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