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Google patents method to measure quantum computer accuracy

This patent describes a statistical method for estimating how accurately a quantum computer performs its calculations. It works by running random test circuits and using a mathematical technique called Bayesian estimation to separate the correct results from the noise inherent in the hardware.

Why it mattersThis is a technical tool for engineers to verify that quantum hardware is working as intended, which is a necessary step before the technology can be used for practical tasks.

In the filing’s own words

Methods, systems and apparatus for estimating the fidelity of a quantum computing system. In one aspect, a method includes defining one or more random quantum circuits, wherein a noisy experimental implementation of each random quantum circuit is approximated by a depolarizing channel with respective polarization parameter; generating, for each defined random quantum circuit and by the quantum computing system, a set of experimental data, wherein data items in the set of experimental data comprise measured bit strings corresponding to experimental implementations of the random quantum circuit; determining, for each of the one or more random quantum circuits, an estimate of the respective polarization parameter, comprising maximizing a log-likelihood of the polarization parameter conditioned on the respective set of experimental data using series inversion; and determining an estimate of the fidelity of the quantum computing system based on the determined estimates of respective polarization parameters.

What exactly they claim (claim 1)

1. A method for estimating the fidelity of a quantum computing system, the method comprising: defining one or more random quantum circuits, wherein a noisy experimental implementation of each random quantum circuit is approximated by a depolarizing channel with respective polarization parameter; generating, for each defined random quantum circuit and by the quantum computing system, a set of experimental data, wherein data items in the set of experimental data comprise measured bit strings corresponding to experimental implementations of the random quantum circuit; determining, for each of the one or more random quantum circuits, an estimate of the respective polarization parameter, comprising: computing, for each measured bit string in the respective set of experimental data, an output probability as a weighted combination of (i) a probability that an ideal implementation of the random quantum circuit produces a measurement eigenstate corresponding to the measured bit string and (ii) a uniform probability over all possible bit strings, wherein weights of the weighted combination are determined based on the polarization parameter; forming a log-likelihood of the polarization parameter based on the computed output probabilities; and maximizing the log-likelihood of the polarization parameter using series inversion; and determining, using the determined estimates of respective polarization parameters, an estimate of the fidelity of the quantum computing system.

Facts

Company
Google (Google LLC)
Official title
Bayesian quantum circuit fidelity estimation
Patent number
US12731065B2
Application number
17623385
Filed
Oct 25, 2019
Granted
Sep 8, 2026
Inventors
3
Claims
14

Classified under

G06N 10/70 Physics & computingG06N 10/20 Physics & computingG06N 10/40 Physics & computing
Read the full filing (official PDF) ↗ Open in the Patent Tracker

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Summaries are simplified from the filing’s own abstract and first claim. A patent filing is not a product announcement.
Patent data and drawings: U.S. Patent and Trademark Office (USPTO). Nebula is not affiliated with or endorsed by the USPTO.