Search

EP-4738207-A1 - INFORMATION PROCESSING APPARATUS, COMPUTER PROGRAM, AND ERROR ESTIMATION METHOD

EP4738207A1EP 4738207 A1EP4738207 A1EP 4738207A1EP-4738207-A1

Abstract

An information processing apparatus identifies a pair of second vertices corresponding to second qubits in which errors are detected through syndrome measurement, the pair being determined to be at a short distance based on a first determination criterion as to whether the distance between the second vertices is long or short. The information processing apparatus determines, based on first weights of first edges included in a path connecting the pair in a first decode graph, a second weight for a second edge connecting the paired second vertices. The information processing apparatus generates a second decode graph that includes the paired second vertices and a second edge connecting the paired second vertices, the second edge being assigned the second weight. Then, the information processing apparatus estimates a third qubit in which an error has occurred, based on the second weight of the second edge in the second decode graph.

Inventors

  • KISHI, Kaito

Assignees

  • FUJITSU LIMITED

Dates

Publication Date
20260506
Application Date
20251027

Claims (8)

  1. An information processing apparatus comprising: processing means (12) for: generating a first decode graph (3) including first vertices corresponding to a plurality of first qubits, respectively, and first edges each connecting the first vertices corresponding to two first qubits among the plurality of first qubits, the plurality of first qubits being used for detecting an error occurring in qubits in a qubit device (1), the two first qubits sharing a same qubit among the qubits as an error detection target, each of the first edges being assigned a first weight based on a probability of detecting an error with the first qubits corresponding to the first vertices at both ends of said each of the first edges; identifying, from among the plurality of first vertices, a pair of second vertices (4a to 4f) corresponding to two different second qubits among a plurality of second qubits in which errors have been detected through syndrome measurement, the second vertices of the pair having been determined to be at a short distance based on a first determination criterion as to whether a distance between the second vertices (4a to 4f) is long or short; determining a second weight for a second edge connecting the second vertices of the pair, based on the first weights of the first edges included in a path connecting the second vertices of the pair in the first decode graph (3); generating a second decode graph (7) including the second vertices of the pair and the second edge connecting the second vertices of the pair, the second edge being assigned the second weight; and estimating a third qubit in which an error has occurred, based on the second weight of the second edge in the second decode graph (7).
  2. The information processing apparatus according to claim 1, wherein identifying of the pair includes dividing a region where the first decode graph (3) exists into a plurality of subregions (3a, 3b, ...), and determining, based on the first determination criterion related to a positional relationship between subregions to which two second vertices under determination belong, whether a distance between the two second vertices under determination is long or short.
  3. The information processing apparatus according to claim 2, wherein determining of the second weight for the second edge includes determining a calculation method for calculating the second weight, according to whether a second determination criterion is satisfied, the second determination criterion being used for determining that a distance between subregions to which the second vertices of the pair belong is short.
  4. The information processing apparatus according to claim 3, wherein the determining of the second weight for the second edge includes determining the second weight using a first calculation method, upon determining that a positional relationship between the subregions to which the second vertices of the pair belong satisfies the second determination criterion, and determining the second weight using a second calculation method, upon determining that the positional relationship does not satisfy the second determination criterion, the second calculation method being less precise than the first calculation method.
  5. The information processing apparatus according to claim 4, wherein the determining of the second weight for the second edge includes calculating, for each of the plurality of subregions in the first decode graph (3), an average weight of the first weights of the first edges in said each of the plurality of subregions, and replacing, upon determining that the second determination criterion is not satisfied, the first weight of each of the first edges with the average weight of the subregion to which said each of the first edges belongs, and determining the second weight.
  6. The information processing apparatus according to any of the preceding claims, wherein identifying of the pair includes preventing a number of pairs, each formed by each of the second vertices and a different second vertex, from exceeding a predetermined upper limit value.
  7. A computer program that causes a computer to perform a process comprising: generating a first decode graph (3) including first vertices corresponding to a plurality of first qubits, respectively, and first edges each connecting the first vertices corresponding to two first qubits among the plurality of first qubits, the plurality of first qubits being used for detecting an error occurring in qubits in a qubit device (1), the two first qubits sharing a same qubit among the qubits as an error detection target, each of the first edges being assigned a first weight based on a probability of detecting an error with the first qubits corresponding to the first vertices at both ends of said each of the first edges; identifying, from among the plurality of first vertices, a pair of second vertices (4a to 4f) corresponding to two different second qubits among a plurality of second qubits in which errors have been detected through syndrome measurement, the second vertices of the pair having been determined to be at a short distance based on a first determination criterion as to whether a distance between the second vertices (4a to 4f) is long or short; determining a second weight for a second edge connecting the second vertices of the pair, based on the first weights of the first edges included in a path connecting the second vertices of the pair in the first decode graph (3); generating a second decode graph (7) including the second vertices of the pair and the second edge connecting the second vertices of the pair, the second edge being assigned the second weight; and estimating a third qubit in which an error has occurred, based on the second weight of the second edge in the second decode graph (7).
  8. An error estimation method executed by a computer, the error estimation method comprising: generating a first decode graph (3) including first vertices corresponding to a plurality of first qubits, respectively, and first edges each connecting the first vertices corresponding to two first qubits among the plurality of first qubits, the plurality of first qubits being used for detecting an error occurring in qubits in a qubit device (1), the two first qubits sharing a same qubit among the qubits as an error detection target, each of the first edges being assigned a first weight based on a probability of detecting an error with the first qubits corresponding to the first vertices at both ends of said each of the first edges; identifying, from among the plurality of first vertices, a pair of second vertices (4a to 4f) corresponding to two different second qubits among a plurality of second qubits in which errors have been detected through syndrome measurement, the second vertices of the pair having been determined to be at a short distance based on a first determination criterion as to whether a distance between the second vertices (4a to 4f) is long or short; determining a second weight for a second edge connecting the second vertices of the pair, based on the first weights of the first edges included in a path connecting the second vertices of the pair in the first decode graph (3); generating a second decode graph (7) including the second vertices of the pair and the second edge connecting the second vertices of the pair, the second edge being assigned the second weight; and estimating a third qubit in which an error has occurred, based on the second weight of the second edge in the second decode graph (7).

Description

FIELD The embodiments discussed herein relate to an information processing apparatus, a computer program, and an error estimation method. BACKGROUND Development of quantum error correction techniques has been advanced in order to implement high-precision quantum computation on a quantum computer. To enable quantum error correction, the state of a single qubit is encoded using a plurality of physical qubits, e.g., in a surface code. The encoded single qubit is referred to as a logical qubit. Errors in the physical qubits constituting a logical qubit may be detected through syndrome measurements using ancilla qubits. The positions of physical qubits in which errors have occurred are detected by decoding the code based on the results of the syndrome measurements. As a quantum error correction technique, for example, a qubit error estimation device has been proposed that estimates errors within a desired time and with a practical code distance, without using approximations such as assuming a constant bit error rate. Techniques have also been proposed for encoding a quantum circuit to a trivalent lattice scheme to identify flag qubit outcomes. Quantum error correction has also been proposed to correct a stream of syndrome measurements. Furthermore, an efficient method for decoding quantum state information has also been proposed. A technique of implementing a decoder responsible for diagnosing noise-induced diagnostic errors on a field-programmable gate array (FPGA) and an application specific integrated circuit (ASIC) has also been proposed. See, for example, the following literatures. Japanese Laid-open Patent Publication No. 2024-59124Japanese National Publication of International Patent Application No. 2022-553169U.S. Patent Application Publication No. 2022/0382632U.S. Patent No. 11847020 Ben Barber, et al., "A real-time, scalable, fast and highly resource efficient decoder for a quantum computer", arXiv: 2309.05558v2, quant-ph, 24-Sep-2024 When a quantum computer sequentially performs the gate operations of a plurality of quantum gates represented in a quantum circuit, it frequently performs syndrome measurements on logical qubits and the estimation of error locations based on the measurement results. Therefore, there is a demand that the computation for estimating error locations in a logical qubit is performed within a short time, for example, within 1 µs. However, conventional error location estimation algorithms have difficulty in estimating error locations within a short time due to a large amount of data used and other reasons. SUMMARY In one aspect, it is desirable to reduce the time needed to estimate error locations in a logical qubit. In one aspect, there is provided an information processing apparatus including: processing unit for: generating a first decode graph including first vertices corresponding to a plurality of first qubits, respectively, and first edges each connecting the first vertices corresponding to two first qubits among the plurality of first qubits, the plurality of first qubits being used for detecting an error occurring in qubits in a qubit device, the two first qubits sharing a same qubit among the qubits as an error detection target, each of the first edges being assigned a first weight based on a probability of detecting an error with the first qubits corresponding to the first vertices at both ends of said each of the first edges; identifying, from among the plurality of first vertices, a pair of second vertices corresponding to two different second qubits among a plurality of second qubits in which errors have been detected through syndrome measurement, the second vertices of the pair having been determined to be at a short distance based on a first determination criterion as to whether a distance between the second vertices is long or short; determining a second weight for a second edge connecting the second vertices of the pair, based on the first weights of the first edges included in a path connecting the second vertices of the pair in the first decode graph; generating a second decode graph including the second vertices of the pair and the second edge connecting the second vertices of the pair, the second edge being assigned the second weight; and estimating a third qubit in which an error has occurred, based on the second weight of the second edge in the second decode graph. BRIEF DESCRIPTION OF DRAWINGS The invention is described, by way of example only, with reference to the following drawings, in which: FIG. 1 illustrates an example of an error estimation method according to a first embodiment;FIG. 2 illustrates an example of a configuration of a quantum computing system;FIG. 3 illustrates an example of hardware of a classical computer and a quantum computer;FIG. 4 illustrates an example of qubit encoding;FIG. 5 illustrates an example of errors occurring in a logical qubit;FIG. 6 illustrates an example of an error location estimation process using a decode graph;