Beating the break-even point by repetitive quantum error correction on a photonic qubit

Quantum error correction (QEC) aims for protecting logic qubits from noises by feedback control. To benefit from QEC, a redundantly encoded logic qubit needs to have a lifetime otherwise unavailable--surpass the "break-even" point. Most QEC codes work by repetitively performing feedback-control cycles, where an error, once occurs, is corrected in real time. Such repetitive QEC demonstrations have been reported on various platforms, but where the break-even point remains to be reached yet. Here we demonstrate a QEC procedure with a logic qubit binomially-encoded in a microwave cavity, dispersively coupled to an ancilla superconducting qubit. By applying a pulse featuring an ingeniously tailored frequency comb to the ancilla, we extract the error syndrome robustly and perform repetitive QEC, thereby exceeding the break-even point by 20%.