Beating the break-even point with autonomous quantum error correction

Abstract

Quantum error correction protects fragile quantum information by encoding it in high-dimensional Hilbert spaces. Conventional protocols typically require repeated syndrome measurements, real-time feedback or post-selection, and multiple physical qubits, which add technical complexity. Here we realize autonomous quantum error correction with a logical qubit encoded in multiple internal spin states of a single trapped ion and surpass the break-even point for qubit lifetime. We use engineered spin–motion couplings to transfer error-induced entropy into motional modes, which is then dissipated by sympathetic cooling with an ancilla ion. This eliminates the need for measurement and feedback. By repeatedly applying this protocol, we observe lifetime extension under both ambient laboratory conditions and injected low-frequency magnetic noise. Our results show that the multilevel structure of trapped ions can support hardware-efficient quantum error correction and robust quantum memories with reduced overhead.