High-throughput bidirectional microwave-to-optical transduction assessed with a practical quantum capacity

A low-noise quantum channel bridging microwave and optical frequencies with high enough throughput to be compatible with qubit lifetimes will be critical for networking superconducting quantum computing nodes. In this talk we present measurements of a transducer based on electromechanical and optomechanical couplings to the vibrational mode of a silicon nitride membrane. Our transducer achieves high signal throughput, while approaching quantum-enabled operation with input-referred added noise of 3 photons. This performance is bidirectional; in downconversion, throughput of this magnitude is unprecedented, and marks an improvement in throughput of nearly four orders of magnitude, and in upconversion, this throughput matches the state-of-the-art demonstration at the few-photon noise level. Using the two-way classically assisted quantum channel capacity, we also find an expression for the maximum rate at which quantum information can propagate through a thermally occupied channel of finite bandwidth, providing a metric that combines the importance of both a quantum transducer's throughput and noise performance.