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EP-4742114-A1 - COMPUTER PROGRAM, QUANTUM GATE CALIBRATION METHOD, AND INFORMATION PROCESSING APPARATUS

EP4742114A1EP 4742114 A1EP4742114 A1EP 4742114A1EP-4742114-A1

Abstract

An information processing apparatus selects a first value for each of a plurality of control parameters for controlling a plurality of pulse signals used by a quantum computer in executing a multi-input quantum gate, estimates a first error from the first values by using an error function for estimating an error between an ideal value and an actual value of the multi-input quantum gate from values of the plurality of control parameters, searches for a second value of each of the plurality of control parameters by using the error function such that a second error estimated from the second values is less than the first error, acquires a result obtained by executing the multi-input quantum gate by using the second values from the quantum computer, and determines a third value to be set to each of the plurality of control parameters by using the result.

Inventors

  • MURAKAMI, RYO

Assignees

  • Fujitsu Limited

Dates

Publication Date
20260513
Application Date
20251103

Claims (8)

  1. A computer program that causes a computer to execute a process comprising: selecting a first value (14a, 15a, 16a) for each of a plurality of control parameters (14 to 16) for controlling a plurality of pulse signals used by a quantum computer in executing a multi-input quantum gate; estimating a first error from the first values by using an error function (13) for estimating an error between an ideal value and an actual value of the multi-input quantum gate from values of the plurality of control parameters; searching for a second value (14b, 15b, 16b) of each of the plurality of control parameters by using the error function such that a second error estimated from the second values is less than the first error; and acquiring a result obtained by executing the multi-input quantum gate by using the second values from the quantum computer, and determining a third value (14c, 15c, 16c) to be set to each of the plurality of control parameters by using the result.
  2. The computer program according to claim 1, wherein the selecting includes measuring an error component (161 to 164) included in a Hamiltonian of the multi-input quantum gate while changing a value of one control parameter (f) of the plurality of control parameters and fixing values of the other control parameters, and selecting a value of the one control parameter that minimizes the measured error component as the first value for the one control parameter, by using the quantum computer.
  3. The computer program according to claim 1 or claim 2, wherein the error function (E) indicates a sum of squares of components included in a matrix difference between a first unitary matrix (ZX) indicating the ideal value and a second unitary matrix (U) indicating the actual value.
  4. The computer program according to any preceding claim, wherein the error function has a plurality of search parameters including coefficients (152) of a Hamiltonian of the multi-input quantum gate, which are mutually convertible with the plurality of control parameters (151), and the searching includes searching for a fourth value for each of the plurality of search parameters by using the error function (E), and converting the fourth values into the second values.
  5. The computer program according to claim 4, wherein the searching includes repeatedly updating values of the plurality of search parameters by using a gradient of the error function (e s ) with respect to the plurality of search parameters (p i ) and a regularization term having a weight (λ) that varies based on an error estimated by the error function.
  6. The computer program according to any preceding claim, wherein the plurality of control parameters include an amplitude (ε CR ) and a phase (φ CR ) of a first pulse signal among the plurality of pulse signals, an amplitude (ε C ) and a phase (φ C ) of a second pulse signal among the plurality of pulse signals, and pulse lengths (t) of the first pulse signal and the second pulse signal.
  7. A quantum gate calibration method executed by a computer, the quantum gate calibration method comprising: selecting a first value (14a, 15a, 16a) for each of a plurality of control parameters (14 to 16) for controlling a plurality of pulse signals used by a quantum computer in executing a multi-input quantum gate; estimating a first error from the first values by using an error function (13) for estimating an error between an ideal value and an actual value of the multi-input quantum gate from values of the plurality of control parameters; searching for a second value (14b, 15b, 16b) of each of the plurality of control parameters by using the error function such that a second error estimated from the second values is less than the first error; and acquiring a result obtained by executing the multi-input quantum gate by using the second values from the quantum computer, and determining a third value (14c, 15c, 16c) to be set to each of the plurality of control parameters by using the result.
  8. An information processing apparatus comprising: memory means (11) for storing an error function (13) for estimating an error between an ideal value and an actual value of a multi-input quantum gate from values of a plurality of control parameters (14 to 16) for controlling a plurality of pulse signals used by a quantum computer in executing the multi-input quantum gate; and processing means (12) for: selecting a first value (14a, 15a, 16a) for each of the plurality of control parameters, estimating a first error from the first values by using the error function, searching for a second value (14b, 15b, 16b) of each of the plurality of control parameters by using the error function such that a second error estimated from the second values is less than the first error, acquiring a result obtained by executing the multi-input quantum gate by using the second values from the quantum computer, and determining a third value (14c, 15c, 16c) to be set to each of the plurality of control parameters by using the result.

Description

FIELD The embodiments discussed herein relate to a computer program, a quantum gate calibration method, and an information processing apparatus. BACKGROUND A quantum computer may emit a pulse signal to a qubit with as a physical implementation of a quantum operation corresponding to a quantum gate. Due to physical restrictions and use environments, the pulse signal to be emitted may fail to be an ideal signal. Thus, the quantum gate may have an error that indicates a deviation from an ideal effect regarding the qubit. Therefore, the quantum computer may have control parameters for adjusting the waveform of the pulse signal, such as the pulse length and the amplitude. The user may perform calibration by measuring the error of the quantum gate of the quantum computer and changing control parameter values so as to reduce the error. For example, optimized randomized benchmarking for immediate turn-up (ORBIT) measures the fidelity of a quantum gate and searches for a control parameter value that maximizes the fidelity with a search algorithm such as the Nelder-Mead method. In addition, among quantum gates, there is a multi-input quantum gate that acts on a plurality of qubits, such as a controlled NOT (CNOT) gate that acts on two qubits. For example, in a cross resonance (CR) method, a pulse signal having a resonance frequency that resonates with a target bit is emitted to a control bit. In this way, the quantum state of the target bit changes depending on the quantum state of the control bit. It is not easy for a quantum computer to implement a multi-input quantum gate with high accuracy by using only one type of pulse signal. Therefore, the quantum computer may implement a multi-input quantum gate by combining a plurality of pulse signals. For example, the quantum computer may emit an additional pulse signal, such as a cancellation tone or a rotary tone, to a qubit, in addition to the main CR pulse. In an analog processor in which quantum devices are arranged in a grid pattern, there is a technique of setting an inter-device coupling value or a local bias value and adjusting a runtime control parameter. There is also a technique in which, at the time of initialization of quantum hardware, each superconducting cavity receives a variable amount of photons such that the photons of the two coupled superconducting cavities interact. There is also a technique for reducing the influence of degeneration in a hybrid computing system including a quantum processor and a digital processor. There is also a technique of modeling a quantum device by using a Hamiltonian matrix and estimating optimum values of physical parameters of the quantum device. See, for example, the following literatures. U.S. Patent Application Publication No. 2011/0298489International Publication Pamphlet No. WO 2015/160401International Publication Pamphlet No. WO 2017/075246International Publication Pamphlet No. WO 2019/005206J. Kelly, R. Barends, B. Campbell, Y. Chen, Z. Chen, B. Chiaro, A. Dunsworth, A.G. Fowler, I. Hoi, E. Jeffrey, A. Megrant, J. Mutus, C. Neill, P.J.J. O'Malley, C. Quintana, P. Roushan, D. Sank, A. Vainsencher, J. Wenner, T.C. White, A.N. Cleland, and John M. Martinis, "Optimal Quantum Control Using Randomized Benchmarking," Physical Review Letters, Volume 112, Issue 24, June 2014Petar Jurcevic, Ali Javadi-Abhari, Lev S. Bishop, Isaac Lauer, Daniela F. Bogorin, Markus Brink, Lauren Capelluto, Oktay Gunluk, Toshinari Itoko, Naoki Kanazawa, Abhinav Kandala, George A. Keefe, Kevin Krsulich, William Landers, Eric P. Lewandowski, Douglas T. McClure, Giacomo Nannicini, Adinath Narasgond, Hasan M. Nayfehl, Emily Pritchett, Mary Beth Rothwell, Srikanth Srinivasan, Neereja Sundaresan, Cindy Wang, Ken X. Wei, Christopher J. Wood, Jeng-Bang Yau, Eric J. Zhang, Oliver E. Dial, Jerry M. Chow, and Jay M. Gambettal, "Demonstration of Quantum Volume 64 on a Superconducting Quantum Computing System", Quantum Science and Technology, Volume 6, Number 2, March 2021 When a multi-input quantum gate is implemented by combining a plurality of pulse signals, the quantum computer may have a plurality of control parameters for adjusting the waveforms of the plurality of pulse signals. However, when the number of control parameters is large, the parameter adjustment method of repeatedly measuring the error of the quantum gates may take a long time to gain the control parameter values at which the error is sufficiently small, and may fail to attain the optimum values within a practical time. SUMMARY In one aspect, an object of the present disclosure is to calibrate quantum gates more efficiently. In one aspect, there is provided a computer program that causes a computer to execute a process including: selecting a first value for each of a plurality of control parameters for controlling a plurality of pulse signals used by a quantum computer in executing a multi-input quantum gate; estimating a first error from the first values by using an error function for