# US 12,182,665 B2 · Characterization of time-correlated quantum errors through entanglement > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,182,665 B2 - Document ID: US12182665B2 - Status: Granted - Kind: B2 - Application number: 17/928,349 - Filed: 2021-05-27 - Published: 2023-11-09 - Granted: 2024-12-31 - Earliest claimed: 2020-05-29 - Assignees: Google Inc. - Applicants: Google LLC - Inventors: Yuezhen Niu; Trevor Johnathan McCourt; Masoud Mohseni; Vadim Smelyanskiy - Web page: https://patentgrep.com/patent/US12182665B2 ## CPC - G06N 10/70: Quantum error correction, detection or prevention, e.g. surface codes or magic state distillation - G06N 10/40: Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control - G06N 20/00: Machine learning - G06N 7/01: Probabilistic graphical models, e.g. probabilistic networks - G06N 10/20: Models of quantum computing, e.g. quantum circuits or universal quantum computers - G06N: COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS ## Abstract Errors that affect a quantum computer can be efficiently measured and characterized by placing the quantum computer in a highly-entangled state such as a Greenberger-Horne-Zeilinger (GHZ) state, accumulating quantum errors in the highly entangled state, and then measuring the accumulated errors. In some approaches, the error characterization includes measuring parity oscillations of the GHZ state and fitting a quantum error model to a power spectrum of the parity oscillations. The fitted quantum error model can be used to select a suitable fault-tolerant error correction scheme for the quantum computer given its environmental noise. ## Claims ### Claim 1 A method of operating a quantum computer, comprising: repeatedly performing a plurality of operations, the plurality of operations comprising initializing N qubits of the quantum computer in a highly entangled state that allows the amplification of quantum errors through coherent phase accumulation, accumulating quantum errors in the highly entangled state, and measuring the accumulated errors; and obtaining an ensemble average of the accumulated errors from repeated performing of the plurality of operations; wherein the repeated performing of the plurality of operations is completed on a measurement time scale less than a characteristic time scale for drift of quantum errors in the quantum computer. ### Claim 2 (depends on 1) The method of claim 1, wherein the highly entangled state selected to amplify quantum errors is a Greenberger-Horne-Zeilinger (GHZ) state. ### Claim 3 (depends on 1) The method of claim 1, wherein measuring the accumulated errors comprises measuring parity oscillations of the highly entangled state for a sequence of phase angles ϕ. ### Claim 4 (depends on 3) The method of claim 3, wherein the sequence of phase angles ϕ is an incremental sequence of phase angles ϕ. ### Claim 5 (depends on 3) The method of claim 3, wherein the sequence of phase angles ϕ is a randomized sequence of phase angles ϕ. ### Claim 6 (depends on 3) The method of claim 3, wherein, for each phase angle ø in the sequence of phase angles, measuring parity oscillations includes: applying an analyzing pulse for the phase angle ϕ to each of the N qubits. ### Claim 7 (depends on 6) The method of claim 6, wherein for each phase angle ϕ in the sequence of phase angles, measuring parity oscillations includes: applying a dynamical decoupling pulse series after the analyzing pulse. ### Claim 8 (depends on 7) The method of claim 7, wherein each of the dynamical decoupling pulse series is a Carr-Purcell-Meiboom-Gill (CPMG) pulse series. ### Claim 9 (depends on 3) The method of claim 3, further comprising: fitting a quantum error model to the ensemble average of the accumulated errors. ### Claim 10 (depends on 9) The method of claim 9, wherein the quantum error model is a Pauli error model. ### Claim 11 (depends on 10) The method of claim 10, wherein: the obtaining of the ensemble average includes obtaining a power spectrum of the parity oscillations as a function of phase frequency ωϕ conjugate to phase angle ϕ; and the fitting of the Pauli error model is a fitting of Pauli phase error probability ρz and Pauli bit-flip error probability ρx to the power spectrum of the parity oscillations. ### Claim 12 (depends on 9) The method of claim 9, further comprising: selecting a quantum error correction scheme corresponding to the fitted quantum error model. ### Claim 13 (depends on 12) The method of claim 12, further comprising: performing, by the quantum computer, a computational process using the selected quantum error correction scheme. ### Claim 14 (depends on 9) The method of claim 9, further comprising: evaluating, based on the fitted quantum error model, a fitness of the quantum computer for a selected computational process. ### Claim 15 A system for operating a quantum computer, the system comprising: one or more processors; one or more I/O devices coupled to the one or more processors and configured to send control signals to and receive readout signals from the quantum computer; and one or more memories having stored thereon computer readable instructions configured to cause the one more processors and the one or more I/O devices to carry out operations on the quantum computer, the operations comprising: repeatedly performing a plurality of operations, the plurality of operations comprising initializing N qubits of the quantum computer in a highly entangled state that allows the amplification of quantum errors through coherent phase accumulation, accumulating quantum errors in the highly entangled state, and measuring the accumulated errors; and obtaining an ensemble average of the accumulated errors from repeated performing of the plurality of operations; wherein the repeated performing of the plurality of operations is completed on a measurement time scale less than a characteristic time scale for drift of quantum errors in the quantum computer. ### Claim 16 (depends on 15) The system of claim 15, wherein the quantum computer is a superconducting quantum computer, an NMR quantum computer, a trapped ion quantum computer, or an atomic quantum computer. ### Claim 17 (depends on 15) The system of claim 15, further comprising: the quantum computer. ### Claim 18 A non-transitory computer readable medium storing instructions for execution by one more or more computers configured to send control signals to and receive readout signals from a quantum computer, the instructions causing the one or more computers to carry out operations on the quantum computer, the operations comprising: repeatedly performing a plurality of operations, the plurality of operations comprising initializing N qubits of the quantum computer in a highly entangled state that allows the amplification of quantum errors through coherent phase accumulation, accumulating quantum errors in the highly entangled state, and measuring the accumulated errors; and obtaining an ensemble average of the accumulated errors from repeated performing of the plurality of operations; wherein the repeated performing of the plurality of operations is completed on a measurement time scale less than a characteristic time scale for drift of quantum errors in the quantum computer.