Optical readout of a superconducting qubit using a piezo-optomechanical transducer

Superconducting quantum processors have made important progress in size and computing potential. However, the practical cryogenic limitations of operating large numbers of superconducting qubits are becoming a bottleneck for further scaling. Due to the low thermal conductivity and the dense optical multiplexing capacity of telecommunications fibre, converting qubit signal processing to the optical domain using microwave-to-optics transduction would substantially relax the strain on cryogenic space and thermal budgets. Here we demonstrate optical readout of a superconducting transmon qubit through an optical fibre connected via a coaxial cable to a fully integrated piezo-optomechanical transducer. Using a demolition readout technique, we achieve a single-shot readout fidelity of 81%. Our results illustrate the benefits of piezo-optomechanical transduction for low-dissipation operation of large quantum processors. Superconducting qubits are measured using microwaves, posing constraints on its size and thermal budgets. The electro-optic transceiver presented here can be used to perform optical readout without affecting qubit performance.