EP-4742115-A1 - QUANTUM CALCULATION SUPPORT PROGRAM, QUANTUM CALCULATION SUPPORT METHOD, AND INFORMATION PROCESSING DEVICE

EP4742115A1EP 4742115 A1EP4742115 A1EP 4742115A1EP-4742115-A1

Abstract

To improve the fidelity of quantum computation in accordance with a dynamic quantum circuit. An information processing apparatus (10) generates, based on a first dynamic quantum circuit (1), a plurality of candidate assignments (3a, 3b, and so on). The information processing apparatus (10) generates, based on the plurality of candidate assignments (3a, 3b, and so on), second dynamic quantum circuits (4a, 4b, and so on) that satisfy a constraint condition (2). The information processing apparatus (10) acquires measurement results at a measurement point (1a) in a plurality of quantum computations executed in accordance with second dynamic quantum circuits corresponding to a part of the plurality of candidate assignments (3a, 3b, and so on). The information processing apparatus (10) calculates, based on the measurement results, an index value affecting fidelity for each of the plurality of candidate assignments (3a, 3b, and so on), the index value representing fidelity when quantum computation is executed in accordance with the corresponding second dynamic quantum circuit (4a, 4b, and so on). The information processing apparatus (10) determines an assignment based on the index value.

Inventors

YAMAGUCHI, MASAOMI

Assignees

FUJITSU LIMITED

Dates

Publication Date: 20260513
Application Date: 20230703

Claims (9)

A quantum computation support program that causes a computer to execute a process comprising: generating, based on a first dynamic quantum circuit in which a gate operation to be executed varies in accordance with a measurement result of a quantum state at a predetermined measurement point for a qubit, a plurality of candidate assignments indicating candidates of a plurality of second qubits in a quantum computer to be assigned to a plurality of first qubits indicated in the first dynamic quantum circuit; generating, based on each of the plurality of candidate assignments, respective second dynamic quantum circuits that are capable of performing a gate operation equivalent to the gate operation of the first dynamic quantum circuit while satisfying a gate-operation-related constraint condition in the quantum computer; acquiring measurement results at the predetermined measurement point in a plurality of quantum computations executed in accordance with the respective second dynamic quantum circuits corresponding to a part of the plurality of candidate assignments; calculating, based on the measurement results, an index value affecting fidelity when the plurality of quantum computations is executed in accordance with the respective second dynamic quantum circuits corresponding to the plurality of candidate assignments; and determining, based on the index value of each of the plurality of candidate assignments, an assignment of the plurality of second qubits to the plurality of first qubits.
The quantum computation support program according to claim 1, wherein: the first dynamic quantum circuit includes a conditional branch circuit that executes one of a first partial circuit and a second partial circuit in accordance with the measurement result at the predetermined measurement point, the generating of the respective second dynamic quantum circuits includes generating the respective second dynamic quantum circuits satisfying the gate-operation-related constraint condition by adding a swap gate to at least one of the first partial circuit and the second partial circuit, and the calculating of the index value includes calculating, as the index value, an expected value of a number of executions of the swap gate when the plurality of quantum computations is executed in accordance with the respective second dynamic quantum circuits corresponding to the plurality of candidate assignments.
The quantum computation support program according to claim 2, wherein: the calculating of the index value includes calculating the expected value based on a number of times the first partial circuit is executed and a number of times the second partial circuit is executed, based on the measurement results at the predetermined measurement point obtained in the plurality of quantum computations executed in accordance with the first dynamic quantum circuit.
The quantum computation support program according to claim 1, wherein: the first dynamic quantum circuit includes a loop circuit that includes the predetermined measurement point and is repeatedly executed based on the measurement result at the predetermined measurement point, the generating of the respective second dynamic quantum circuits includes generating the respective second dynamic quantum circuits that satisfy the gate-operation-related constraint condition by adding a swap gate to the loop circuit, and the calculating of the index value includes calculating, as the index value, an expected value of a number of executions of the swap gate based on an average number of repetitions of the loop circuit when the plurality of quantum computations is executed in accordance with the respective second dynamic quantum circuits.
The quantum computation support program according to claim 1, wherein: the acquiring of the measurement results and the calculating of the index value are alternately repeated N times (N being a natural number), the acquiring of the measurement results includes, after a second time, determining a first candidate assignment based on the index value of each of the plurality of candidate assignments calculated immediately before, and acquiring the measurement results at the predetermined measurement point in a plurality of quantum computations executed in accordance with one of the respective second dynamic quantum circuits corresponding to the first candidate assignment, and the determining of the assignment of the plurality of second qubits includes determining the assignment of the plurality of second qubits to the plurality of first qubits based on the index value of each of the plurality of candidate assignments calculated in an N-th calculating of the index value.
The quantum computation support program according to claim 1, wherein: the determining of the assignment of the plurality of second qubits includes determining the assignment of the plurality of second qubits to the plurality of first qubits based on a second candidate assignment from among the plurality of candidate assignments, the second candidate assignment having the index value indicating that the fidelity is higher than the fidelity indicated by the index value of each of the plurality of candidate assignments other than the second candidate assignment.
The quantum computation support program according to any of claims 1 to 6, wherein: the process further includes outputting, as a computation result of the first dynamic quantum circuit, a result of the plurality of quantum computations executed by the quantum computer in accordance with one of the respective second dynamic quantum circuits corresponding to the determined assignment.
A quantum computation support method executed by a computer, the quantum computation support method comprising: generating, based on a first dynamic quantum circuit in which a gate operation to be executed varies in accordance with a measurement result of a quantum state at a predetermined measurement point for a qubit, a plurality of candidate assignments indicating candidates of a plurality of second qubits in a quantum computer to be assigned to a plurality of first qubits indicated in the first dynamic quantum circuit; generating, based on each of the plurality of candidate assignments, respective second dynamic quantum circuits that are capable of performing a gate operation equivalent to the gate operation of the first dynamic quantum circuit while satisfying a gate-operation-related constraint condition in the quantum computer; acquiring measurement results at the predetermined measurement point in a plurality of quantum computations executed in accordance with the respective second dynamic quantum circuits corresponding to a part of the plurality of candidate assignments; calculating, based on the measurement results, an index value affecting fidelity when the plurality of quantum computations is executed in accordance with the respective second dynamic quantum circuits corresponding to the plurality of candidate assignments; and determining, based on the index value of each of the plurality of candidate assignments, an assignment of the plurality of second qubits to the plurality of first qubits.
An information processing apparatus comprising: a processing unit for: generating, based on a first dynamic quantum circuit in which a gate operation to be executed varies in accordance with a measurement result of a quantum state at a predetermined measurement point for a qubit, a plurality of candidate assignments indicating candidates of a plurality of second qubits in a quantum computer to be assigned to a plurality of first qubits indicated in the first dynamic quantum circuit, generating, based on each of the plurality of candidate assignments, respective second dynamic quantum circuits that are capable of performing a gate operation equivalent to the gate operation of the first dynamic quantum circuit while satisfying a gate-operation-related constraint condition in the quantum computer, acquiring measurement results at the predetermined measurement point in a plurality of quantum computations executed in accordance with the respective second dynamic quantum circuits corresponding to a part of the plurality of candidate assignments, calculating, based on the measurement results, an index value affecting fidelity when the plurality of quantum computations is executed in accordance with the respective second dynamic quantum circuits corresponding to the plurality of candidate assignments, and determining, based on the index value of each of the plurality of candidate assignments, an assignment of the plurality of second qubits to the plurality of first qubits.

Description

Technical Field The embodiments discussed herein relate to a quantum computation support program, a quantum computation support method, and an information processing apparatus. Background Art A computation performed by a quantum computer is represented as a quantum circuit. A quantum circuit indicates gate operations to be applied to qubits. Each qubit indicated in a quantum circuit is assigned to a qubit in a quantum device (hereinafter referred to as a physical qubit). The quantum computer executes, for a circuit qubit indicated in the quantum circuit, a gate operation on the physical qubit corresponding to that circuit qubit. As a result, the state of the physical qubit changes. When the quantum circuit includes an instruction to measure the state of the circuit qubit, the quantum computer measures the state of the physical qubit corresponding to the circuit qubit and stores the result in a classical bit. A quantum circuit corresponding to a problem to be solved is described using various types of quantum gates. However, quantum gates executable by the quantum computer (native gates) are limited to a subset of quantum gates. Therefore, an initial quantum circuit is converted into a quantum circuit composed solely of native gates. In addition, in a quantum computer, a pair of qubits on which a two-qubit gate operation is executable is limited to a pair of qubits adjacent to each other in topology. Accordingly, in the conversion of a quantum circuit, when a two-qubit gate is present, a pair of circuit qubits in the quantum circuit on which the two-qubit gate is to operate is assigned to a pair of physical qubits adjacent to each other in topology. If such an assignment is not possible, a swap gate is added to the converted quantum circuit. By adding a swap gate, each physical qubit corresponding to each circuit qubit on which the gate operation is to be performed is changed to one that is adjacent in topology. The number of swap gates to be added depends on the assignment relationship between the physical qubits and the circuit qubits in the initial state. The number of swap gates affects the fidelity of quantum computation using the quantum circuit. Fidelity is a performance index indicating how closely the operation of qubits approximates an ideal operation. As the number of swap gates increases, the fidelity decreases. Therefore, the assignment of physical qubits to circuit qubits is performed such that the number of swap gates included in the converted quantum circuit is minimized. Note that the quantum circuit may include a conditional branch circuit (for example, if-else) that selects a series of gate operations to be executed according to a measurement result. The quantum circuit may also include a loop circuit that repeats processing according to a measurement result. The measurement result in the quantum circuit is unknown until the quantum circuit is executed, and the branch destination of the conditional branch circuit and the number of repetitions of the loop circuit are not determined before executing the quantum circuit. Accordingly, for example, a method for estimating the fidelity of quantum hardware has been proposed. A method for optimizing a quantum circuit that includes a step of replacing an identified set of quantum circuit gates with a template of quantum circuit gates has also been proposed. The template of quantum circuit gates in this method has a lower quantum cost than the identified set of quantum circuit gates. Furthermore, a method has been proposed in which the fidelity of each subcircuit is estimated, and an estimated fidelity of a quantum processor is obtained by multiplying the estimated circuit fidelities of the respective subcircuits. In addition, a method has been proposed that enables standard verification of the reliability of a quantum device and estimates a quantum state with fewer resources. Citation List Patent Literature PTL1: Japanese Laid-open Patent Publication No. 2022-167926PTL2: Japanese National Publication of International Patent Application No. 2022-521143PTL3: U.S. Patent Application Publication No. 2022/0383180PTL4: U.S. Patent Application Publication No. 2021/0374589 Summary of Invention Technical Problem However, in conventional techniques for converting a quantum circuit, a relationship between an assignment of physical qubits to respective qubits indicated in a dynamic quantum circuit including a conditional branch circuit or a loop circuit and the number of swap gates to be executed is not sufficiently taken into consideration. As a result, the number of executions of swap gates becomes excessive, and the fidelity of quantum computation deteriorates in some cases. In one aspect, this disclosure is intended to improve the fidelity of quantum computation in accordance with a dynamic quantum circuit. Solution to Problem In one aspect, a quantum computation support program is provided that causes a computer to execute the following processing. The co