Calibrated decoders for experimental quantum error correction

TL;DR

This paper demonstrates a quantum memory preservation method using calibrated decoders and flagged error events, achieving logical error rates below physical measurement errors, thus advancing quantum error correction techniques.

Contribution

Introduces a calibrated perfect matching decoder with flagged error events for improved quantum error correction in quantum memories.

Findings

Logical error rate per round was reduced to 5.1×10^{-4} with full post-selection.

The method surpasses the physical measurement error rate, indicating effective error correction.

Using flagged error events and calibration enhances decoder performance in quantum error correction.

Abstract

Arbitrarily long quantum computations require quantum memories that can be repeatedly measured without being corrupted. Here, we preserve the state of a quantum memory, notably with the additional use of flagged error events. All error events were extracted using fast, mid-circuit measurements and resets of the physical qubits. Among the error decoders we considered, we introduce a perfect matching decoder that was calibrated from measurements containing up to size-4 correlated events. To compare the decoders, we used a partial post-selection scheme shown to retain ten times more data than full post-selection. We observed logical errors per round of $2.2\pm0.1\times10^{-2}$ (decoded without post-selection) and $5.1\pm0.7\times10^{-4}$ (full post-selection), which was less than the physical measurement error of $7\times10^{-3}$ and therefore surpasses a pseudo-threshold for repeated logical measurements.