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DE-112022000582-B4 - Mitigation of the readout error in quantum computation

DE112022000582B4DE 112022000582 B4DE112022000582 B4DE 112022000582B4DE-112022000582-B4

Abstract

System (120) which features: a processor (260) that executes computer-executable components stored in memory (270), wherein the computer-executable components include: a compilation component (230) that encodes one or more qubits (140) according to a ring-shaped repetition code at a time after operations on the one or more qubits and before readout, wherein the computer-executable components further comprise a branch detection component (220) that detects a first chain of several auxiliary qubits associated with a specific qubit of the one or more qubits (140), a second chain of several auxiliary qubits associated with the specific qubit, and a marker qubit that combines the first chain of auxiliary qubits and the second chain of auxiliary qubits, wherein the encoding of the one or more qubits comprises encoding the specific qubit by: Encoding the first chain of auxiliary qubits using repetition encoding; and Encoding the second chain of auxiliary qubits using repetition coding.

Inventors

  • Panagiotis Barkoutsos
  • Jakob Max Guenther
  • Francesco Tacchino
  • James Robin Wootton
  • Ivano Tavernelli

Assignees

  • INTERNATIONAL BUSINESS MACHINES CORPORATION

Dates

Publication Date
20260513
Application Date
20220318
Priority Date
20210319

Claims (17)

  1. System (120) comprising: a processor (260) that executes computer-executable components stored in memory (270), wherein the computer-executable components comprise: a compilation component (230) that encodes one or more qubits (140) according to a ring-shaped repeat code at a time after operations on the one or more qubits and before readout, wherein the computer-executable components further comprise a branch detection component (220) comprising a first chain of several auxiliary qubits associated with a particular qubit of the one or the several qubits (140), a second chain of several auxiliary qubits associated with the particular qubit, and a marker qubit that recognizes the first chain of auxiliary qubits and the second chain of auxiliary qubits, wherein the encoding of the one or the several qubits includes encoding the particular qubit by: encoding the first chain of auxiliary qubits using repetition encoding; and encoding the second chain of auxiliary qubits using repetition encoding.
  2. System (120) according to Claim 1 , wherein the one or more qubits (140) have several qubits and wherein the encoding comprises the ring-shaped repetition encoding of a first qubit of the several qubits and a second qubit of the several qubits in parallel and independently of each other.
  3. System (120) according to Claim 1 , which further comprises a monitoring component (240) that causes quantum hardware (130) to measure a state of the marker qubit, wherein the state represents a combination of faulty coding and fault-free coding of the specified qubit.
  4. System (120) according to Claim 1 , wherein a controlled NOT gate (CNOT gate) connects the marker qubit and an end auxiliary qubit of the first chain of auxiliary qubits, and wherein a second CNOT connects the marker qubit and an end auxiliary qubit of the second chain of auxiliary qubits.
  5. System (120) according to Claim 1 , wherein the specified qubit, the first chain of auxiliary qubits, the second chain of auxiliary qubits and the marker qubit are arranged in a layout (300) that has ring-shaped connectivity.
  6. System (120) according to Claim 1 , wherein one or more qubits (140) are contained in a qubit layout that exhibits strong hexagonal connectivity.
  7. System (120) according to Claim 1 , wherein the one or more qubits (140) form a quantum processor of a cloud-based quantum computer (130) or a local quantum computer (130).
  8. A computer-implemented method comprising: causing a processor (260) to encode one or more qubits (140) according to a ring-shaped repeat code at a time after operations on the one or more qubits and before readout, the method further comprising recognizing, by the processor (260), a first chain of several auxiliary qubits associated with a specific qubit of the one or more qubits (140), a second chain of several auxiliary qubits associated with the specific qubit, and a marker qubit that combines the first chain of auxiliary qubits and the second chain of auxiliary qubits, wherein the encoding of the one or more qubits comprises encoding the specific qubit by: encoding the first chain of auxiliary qubits according to a recovery encoding; and encoding the second chain of auxiliary qubits according to a recovery encoding.
  9. Computer-implemented method according to Claim 8 , wherein the one or the several qubits (140) comprise several qubits and wherein the encoding of the one or the several qubits comprises the encoding of a first qubit of the several qubits and a second qubit of the several qubits in parallel and independently of each other.
  10. Computer-implemented method according to Claim 8 , which further includes the processor (260) causing quantum hardware (130) to measure a state of the marker qubit, wherein the state is a faulty encoding or a fault-free encoding of the specified qubit.
  11. Computer-implemented method according to Claim 8 , which further includes the application of the encoding of one or more qubits (140) in a quantum computation of time propagation of a quantum observable by the processor.
  12. Computer-implemented method according to Claim 8 , which further includes the application of the encoding of one or more qubits (140) in a quantum variation algorithm by the processor (260).
  13. Computer-implemented method according to Claim 8 , wherein the specified qubit, the first chain of auxiliary qubits, the second chain of auxiliary qubits and the marker qubit are arranged in a layout (300) that has ring-shaped connectivity.
  14. Computer program product for mitigating readout errors in quantum computing, wherein the computer program product comprises a computer-readable storage medium (270) containing program instructions embodied therein, wherein the program instructions are executable by a processor (260) in order to to cause the processor to: cause the processor (260) to encode one or more qubits (140) according to a ring-shaped repeat code at a time after operations on the multiple qubits and before readout, wherein the program instructions are further executable by the processor (260) to cause the processor to recognize a first chain of multiple auxiliary qubits associated with a particular qubit of the one or more qubits, a second chain of multiple auxiliary qubits associated with the particular qubit, and a marker qubit that combines the first chain of auxiliary qubits and the second chain of auxiliary qubits, and wherein the encoding of the one or more qubits comprises encoding the particular qubit by: encoding the first chain of auxiliary qubits using repeat encoding; and encoding the second chain of auxiliary qubits using repeat encoding.
  15. Computer program product according to Claim 14 , wherein the one or the several qubits (140) comprise several qubits and wherein the encoding of the one or the several qubits comprises the parallel encoding of a first qubit of the several qubits and a second qubit of the several qubits.
  16. Computer program product according to Claim 14 , wherein the program instructions are further executable by the processor (260) to cause the processor to cause quantum hardware (130) to measure a state of the marker qubit, wherein the state is a faulty encoding or a fault-free encoding of the multiple qubits.
  17. Computer program product according to Claim 14 , wherein the specified qubit, the first chain of auxiliary qubits, the second chain of auxiliary qubits and the marker qubit are arranged in a layout (300) that has ring-shaped connectivity.

Description

BACKGROUND One or more embodiments of the invention relate to a mitigation of the readout error in a quantum calculation. Quantum computers are built from quantum units connected to an environment that can disrupt and relax the coherence of quantum information contained within the quantum unit. Thus, such units can be exposed to external noise. Consequently, a quantum processor formed by quantum units can be noisy, and errors can occur in the quantum calculations in which the quantum processor is used. Such noise and errors can exist regardless of the architecture of the quantum units. A readout error can arise from a quantum measurement of the quantum units used in a quantum calculation after the quantum units have been manipulated according to the operations that define the quantum calculation. Accordingly, improved technologies to mitigate the readout error may be desirable. The article " “Repetition code of 15 qubits” by James R. Wootton and Daniel Loss, published in “Physical Review A, Vol. 97, 2018, No. 5, Article no. 052313, 7 pp. ISSN 2469-9926”, accessed on 2025-12-02 at https://doi.org/10.1103/PhysRevA.97.052313 describes an implementation of repetition codes for quantum computers using a lookup table decoding of an error syndrome. The article " “Quantum error correction” by Todd A. Brun, available at https://arxiv.org/abs/1910.03672v1 and accessed on 2025-12-02 describes methods and aspects of quantum error correction. SUMMARY The following summary serves to provide a basic understanding of one or more embodiments of the invention. This summary is not intended to identify important or decisive elements, nor to outline any scope of protection for the embodiments in question or for the claims. Its sole purpose is to present concepts in a simplified form as an introduction to the more detailed description that follows. According to one embodiment, a system is provided. The system includes a processor that executes computer-executable components stored in memory. Among the computer-executable components is a compilation component that encodes one or more qubits according to a ring-shaped repeat code at a time point after operations on the one or more qubits and before readout. Thus, measurements that define readout are the only operations that act on an encoded qubit state or states, while all other operations that describe the preparation of the common state of the one or more qubits can be performed without encoding. Therefore, encoding the one or more qubits using a ring-shaped repeat code can reduce readout errors in a quantum computation involving the encoded qubit(s). Furthermore, or in other embodiments, the computer-executable components also include a branch detection component that detects a chain of auxiliary qubits associated with a specific qubit of the one or more qubits, a second chain of auxiliary qubits associated with the specific qubit, and a flag qubit that combines the first chain of auxiliary qubits and the second chain of auxiliary qubits. The encoding of the one or more qubits comprises encoding the specific qubit by encoding the first chain of auxiliary qubits using repetition encoding and encoding the second chain of auxiliary qubits using repetition encoding. According to a further embodiment, a computer-implemented method is provided. The computer-implemented method comprises a processor encoding one or more qubits according to a ring-shaped repetition code at a time point after operations on the one or more qubits and before readout. According to a further embodiment, a computer program product for mitigating readout errors in quantum computing. The computer program product comprises a computer-readable storage medium containing program instructions. The program instructions are executable by a computer to cause the processor to read one or more qubits according to a ring-shaped repetition code at a time after Opera. to encode the ions on the multiple qubits and before reading them out. BRIEF DESCRIPTION OF THE DRAWINGS 1 illustrates a non-restrictive example of an operating environment for readout error mitigation in a quantum computation according to one or more embodiments described herein.2 illustrates a non-restrictive example of a data processing system for readout error mitigation in quantum computing according to one or more embodiments described herein.3 Illustrates a schematic non-restrictive example of a closed chain of qubit units for ring-shaped repetition encoding of a particular qubit unit within the chain according to one or more embodiments described herein.4A schematically illustrates a temporal relationship between a unitary (U) representing operations on a single qubit and another unit (U coding ) representing a ring-shaped repetition coding of the single qubit according to one or more embodiments described herein.4B schematically illustrates a temporal relationship between a unit (U) performing operations on two qubits and two units (U (0) encoding an