Calibrated Decoders for Experimental Quantum Error Correction

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, midcircuit 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-four correlated events. To compare the decoders, we used a partial postselection scheme shown to retain ten times more data than full postselection. We observed logical errors per round of 2.2 +/- 0.1 x 10(-2) (decoded without postselection) and 5.1 +/- 0.7 x 10(-4) (full postselection), which was less than the physical measurement error of 7 x 10(-3) and therefore surpasses a pseudothreshold for repeated logical measurements.

Automated summary

Arbitrarily long quantum computations require quantum memories that can be repeatedly measured without being corrupted. In this study, the researchers were able to preserve the state of a quantum memory by using flagged error events. Fast, midcircuit measurements and resets of the physical qubits were used to extract all error events. A perfect matching decoder was introduced for comparison with other error decoders, and it was calibrated using measurements containing up to size-four correlated events. The researchers observed logical errors per round that surpass the physical measurement error, demonstrating the potential for repeated logical measurements.