Realizing Repeated Quantum Error Correction in a Distance-Three Surface Code

TL;DR

This paper demonstrates repeated quantum error correction using a distance-three surface code on a 17-qubit superconducting circuit, showing preservation of logical qubit states with low error probability, advancing towards fault-tolerant quantum computing.

Contribution

First implementation of repeated, high-speed quantum error correction cycles with a distance-three surface code on superconducting qubits, demonstrating practical fault-tolerance progress.

Findings

Low error probability of 3% per cycle when rejecting leakage

Successful preservation of four logical qubit states

Device characteristics match numerical models

Abstract

Quantum computers hold the promise of solving computational problems which are intractable using conventional methods. For fault-tolerant operation quantum computers must correct errors occurring due to unavoidable decoherence and limited control accuracy. Here, we demonstrate quantum error correction using the surface code, which is known for its exceptionally high tolerance to errors. Using 17 physical qubits in a superconducting circuit we encode quantum information in a distance-three logical qubit building up on recent distance-two error detection experiments. In an error correction cycle taking only $1.1\,\mu$s, we demonstrate the preservation of four cardinal states of the logical qubit. Repeatedly executing the cycle, we measure and decode both bit- and phase-flip error syndromes using a minimum-weight perfect-matching algorithm in an error-model-free approach and apply corrections in postprocessing. We find a low error probability of $3\,\%$ per cycle when rejecting experimental runs in which leakage is detected. The measured characteristics of our device agree well with a numerical model. Our demonstration of repeated, fast and high-performance quantum error correction cycles, together with recent advances in ion traps, support our understanding that fault-tolerant quantum computation will be practically realizable.