Optimized piezo-optomechanical quantum transducer on a hybrid lithium niobate-silicon material platform*

Coherent transduction of single photons from microwave to optical frequencies is expected to play a key role in future quantum networks and distributed quantum computers. We present the design of a piezo-optomechanical quantum transducer optimized for high conversion efficiency and low added noise. In our device, transduction is mediated by a strongly hybridized acoustic mode of a lithium niobate piezoacoustic cavity attached to a silicon optomechanical crystal. This hybrid material platform allows us to design for strong microwave photon-phonon coupling without compromising optomechanical cooperativity. Crucially, we use an acoustic wavelength-scale piezo volume to minimize participation of the lossy piezo region in both electrical and acoustic modes. The resulting transducer acoustic mode is almost silicon-like with single photon piezoelectric and optomechanical coupling rates of MHz-order and an estimated mechanical decoherence rate of order 10kHz. We estimate an intrinsic efficiency of order 10% with <0.5 added noise quanta when resonantly coupled to a typical 5 GHz transmon qubit and operated in pulsed mode at 10 kHz repetition rate. A transducer in this regime is suitable to realize probabilistic schemes for remote entanglement of superconducting quantum processors.