Implemented with continuous-wave control fields only, this passive protocol protects the quantum information by autonomously correcting single-photon-loss errors and boosts the coherence time of the bosonic qubit by over a factor of two. Here we encode a logical qubit in Schrödinger cat-like multiphoton states.sup.15 of a superconducting cavity, and demonstrate a corrective dissipation process that stabilizes an error-syndrome operator: the photon number parity. In principle, QEC can be realized autonomously and continuously by tailoring dissipation within the quantum system.sup.1,8,9,10,11,12,13,14, but so far it has remained challenging to achieve the specific form of dissipation required to counter the most prominent errors in a physical platform. Existing demonstrations of QEC are based on an active schedule of error-syndrome measurements and adaptive recovery operations.sup.2,3,4,5,6,7 that are hardware intensive and prone to introducing and propagating errors. Abstract : To build a universal quantum computer from fragile physical qubits, effective implementation of quantum error correction (QEC).sup.1 is an essential requirement and a central challenge.

Cat code quantum error correction