Approximate gate and supercontrolled unitary gate decompositions for two-qubit operations

• US 10,474,960 B1
• Filed: 10/25/2018
• Issued: 11/12/2019
• Est. Priority Date: 10/25/2018
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Bishop, Lev Samuel
• Primary Examiner(s): Tan, Vibol
• Application Number:
  US16/171,108
• Time in Patent Office: 383 Days
• CPC Class Codes: G06N 10/00 Quantum computing, i.e. information processing based on quantum-mechanical phenomena
• CPC Class Codes: G06N 20/00 Machine learning
• CPC Class Codes: G06N 99/00 Subject matter not provided for in other groups of this subclass
• CPC Class Codes: H03K 19/195 using superconductive devices
• CPC Class Codes: H03K 19/20 characterised by logic function, e.g. AND, OR, NOR, NOT circuits H03K19/003 - H03K19/01 take precedence

Abstract

Techniques are provided for improving quantum circuits. The technology includes approximately expanding, by a system operatively coupled to a processor, using zero to a number of applications of a super controlled basis gate, a target two-qubit operation, with the approximately expanding resulting in instances of the target two-qubit operation corresponding to the zero to the number of applications, and the target two-qubit operation is part of a source quantum circuit associated with a quantum computer. The system analyzes the instances and the super controlled basis gate, and automatically rewrites the source quantum circuit into a deployed quantum circuit based on the analyzing.

Claims

1. A computer-implemented method, comprising:

approximately expanding, by a system operatively coupled to a processor, using zero to a number of applications of a specific super controlled basis gate, a target two-qubit operation, wherein the approximately expanding results in instances of the target two-qubit operation corresponding to the zero to the number of applications, and the target two-qubit operation is part of a source quantum circuit associated with a quantum computer;

analyzing, by the system, the instances and the specific super controlled basis gate; and

automatically rewriting, by the system, the source quantum circuit into a deployed quantum circuit based on the analyzing.

2. The computer-implemented method of claim 1, further comprising:

identifying one or more super controlled basis gates based on characteristics of the quantum computer; and

selecting the specific super controlled basis gate from the one or more super controlled basis gates.

3. The computer-implemented method of claim 1, wherein the approximately expanding comprises:

determining Weyl chamber representations of the target two-qubit operation and the specific super controlled basis gate;

modifying one or more of the Weyl chamber representations; and

exactly expanding using the one or more modified Weyl chamber representations.

4. The computer-implemented method of claim 1, wherein the analyzing the instances comprises determining a predicted fidelity of the instances.

5. The computer-implemented method of claim 4, wherein the automatically rewriting is based on a maximum predicted fidelity of the instances, and wherein a maximum predicted fidelity of an instance of the instances is based on multiplying the predicted fidelity of the instance by a predicted fidelity of a super controlled basis gate raised to a power of a total number of the specific super controlled basis gates used by the instance.

6. The computer-implemented method of claim 1, wherein the automatically rewriting the source quantum circuit into the deployed quantum circuit improves processing performance of the deployed quantum circuit.

7. A computer-implemented method, comprising:

approximately expanding, by a system operatively coupled to a processor, using zero to a number of applications of a specific super controlled basis gate, a target two-qubit operation, wherein the approximately expanding results in instances of the target two-qubit operation corresponding to the zero to the number of applications, the target two-qubit operation is part of a source quantum circuit associated with a quantum computer, and the instances comprise expansions of both the target two-qubit operation and the target two-qubit operation concatenated with an exchange of the two qubits;

determining, by the system, an average fidelity of at least one of the approximately expanded instances; and

automatically rewriting, by the system, the source quantum circuit into a deployed quantum circuit based on the average fidelity of at least one of the instances.

8. The computer-implemented method of claim 7, wherein the approximately expanding comprises:

determining Weyl chamber representations of the target two-qubit operation, the target two-qubit operation concatenated with an exchange of the two qubits, and the specific super controlled basis gate;

modifying one or more of the Weyl chamber representations; and

exactly expanding using the one or more modified Weyl chamber representations.

9. The computer-implemented method of claim 7, wherein the automatically rewriting is further based on a maximum predicted fidelity of the instances, and wherein a maximum predicted fidelity of an instance of the instances is based on multiplying the average fidelity of the instance by a predicted fidelity of a super controlled basis gate raised to a power of a total number of the specific super controlled basis gates used by the instance.

10. The computer-implemented method of claim 7, further comprising:

executing, by the system, the deployed quantum circuit to obtain measurement data corresponding to the source quantum circuit; and

outputting, by the system, the measurement data.

11. The computer-implemented method of claim 7, wherein the automatically rewriting the source quantum circuit into the deployed quantum circuit improves processing performance of the deployed quantum circuit.

12. The computer-implemented method of claim 7, wherein the automatically rewriting is further based on minimizing a number of two-qubit operations required to implement a containing quantum circuit of the source quantum circuit.

13. The computer-implemented method of claim 7, wherein the specific super controlled basis gate is a CNOT gate.

14. A system, comprising:

a memory that stores computer executable components; and

a processor that executes computer executable components stored in the memory, wherein the computer executable components comprise;

a circuit expanding component that approximately expands, using zero to a number of applications of a specific super controlled basis gate, an identified block of consecutive operations on pairs of qubits, wherein the approximately expanding results in instances of the identified block corresponding to the zero to the number of applications, and the identified block is part of a source quantum circuit associated with a quantum computer;

an analyzer component that analyzes the instances; and

a circuit rewriting component that rewrites the source quantum circuit into a quantum processing unit (QPU) hardware circuit based on the analyzing the instances.

15. The system of claim 14, wherein the circuit expanding component approximately expands the identified block of consecutive operations by using Weyl chamber representations.

16. The system of claim 14, wherein the analyzer component analyzes the instances based on a determination of a predicted fidelity of the instances.

17. A computer-implemented method, comprising:

approximately expanding, by a system operatively coupled to a processor, using zero to a number of applications of a basis gate, a target two-qubit operation, wherein the approximately expanding results in instances of the target two-qubit operation corresponding to the zero to the number of applications, the basis gate is selected based on a similarity to a super controlled basis gate, and the target two-qubit operation is part of a source quantum circuit associated with a quantum computer;

analyzing, by the system, the instances; and

automatically rewriting, by the system, the source quantum circuit into a deployed quantum circuit based on the analyzing the instances.

18. The computer-implemented method of claim 17, wherein the approximately expanding the target two-qubit operation comprises approximately expanding the target two-qubit operation by using Weyl chamber representations.

19. The computer-implemented method of claim 17, further comprising reducing deviations due to differences between the basis gate and the super controlled basis gate, by local optimization of single-qubit gates by fine tuning results of the approximately expanded target two-qubit operation.

20. The computer-implemented method of claim 19, wherein the fine tuning comprises employing a gradient-descent algorithm to reduce the deviations due to differences between the basis gate and the super controlled basis gate by acting on the single-qubit gates.

21. The computer-implemented method of claim 17, wherein the analyzing the instances comprises determining a predicted fidelity of the instances.

22. The computer-implemented method of claim 17, further comprising:

executing, by the system, the deployed quantum circuit to obtain measurement data corresponding to the source quantum circuit; and

outputting, by the system, the measurement data.

23. The computer-implemented method of claim 17, wherein the automatically rewriting the source quantum circuit into the deployed quantum circuit improves processing performance of the deployed quantum circuit.

24. A computer program product facilitating rewriting a source quantum circuit into a deployed quantum circuit associated with a quantum computer, the computer program product comprising a non-transitory computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to:

approximately expand, using zero to a number of applications of a specific super controlled basis gate, a target two-qubit operation, wherein the approximately expanding results in instances of the target two-qubit operation corresponding to the zero to the number of applications, and the target two-qubit operation is part of a source quantum circuit associated with a quantum computer;

analyze the instances and the specific super controlled basis gate; and

automatically rewrite the source quantum circuit into a deployed quantum circuit based on the analyzing.

25. The computer program product of claim 24, wherein the approximately expanding comprises:

determining Weyl chamber representations of the target two-qubit operation and the specific super controlled basis gate;

modifying one or more of the Weyl chamber representations; and

exactly expanding using the one or more modified Weyl chamber representations.