Improved optical cavity in microwave-mechanical-optical transducer*

Linking quantum computational nodes to form a long-distance network in an architecture based on superconducting qubits faces an inherent challenge: the low excitation energy of microwave photons precludes quantum signal propagation at room temperature. A quantum coherent transducer between microwave and optical frequencies would overcome this difficulty. By coupling both a superconducting LC resonator and an optical Fabry-Perot cavity to the same MHz-frequency mode of a SiN membrane micromechanical oscillator, we realize a converter with 47% efficiency [1]. The process adds 38 photons of noise which prevent its quantum operation, with a significant contribution associated with the optical pump mediating the optomechanical interaction. By redesigning the optical cavity, we have reduced misalignment-induced optical loss and enabled greater optomechanical coupling, allowing reduced pump powers.

[1] Higginbotham, A. P., et. al. “Harnessing electro-optic correlations in an efficient mechanical converter,” Nature Physics 14, 1038-1042 (2018)