Repeated quantum error correction on a continuously encoded qubit by real-time feedback

TL;DR

This paper demonstrates active, real-time quantum error correction on a continuously encoded qubit using a diamond quantum processor, significantly improving error resilience and preserving quantum states beyond physical qubit dephasing times.

Contribution

It introduces a method for active error correction with real-time feedback on a continuously protected qubit, advancing fault-tolerant quantum computation capabilities.

Findings

Active error correction extends qubit coherence beyond physical limits

Correlated environmental errors can be effectively corrected

Repeated error correction prevents error accumulation

Abstract

Reliable quantum information processing in the face of errors is a major fundamental and technological challenge. Quantum error correction protects quantum states by encoding a logical quantum bit (qubit) in multiple physical qubits. To be compatible with universal fault-tolerant computations, it is essential that the states remain encoded at all times and that errors are actively corrected. Here we demonstrate such active error correction on a continuously protected qubit using a diamond quantum processor. We encode a logical qubit in three long-lived nuclear spins, repeatedly detect phase errors by non-destructive measurements using an ancilla electron spin, and apply corrections on the encoded state by real-time feedback. The actively error-corrected qubit is robust against errors and multiple rounds of error correction prevent errors from accumulating. Moreover, by correcting correlated phase errors naturally induced by the environment, we demonstrate that encoded quantum superposition states are preserved beyond the dephasing time of the best physical qubit used in the encoding. These results establish a powerful platform for the fundamental investigation of error correction under different types of noise and mark an important step towards fault-tolerant quantum information processing.