Minimizing high-power dielectric loss and noise in a mechanically-mediated electro-optic transducer

A quantum network based on microwave-frequency superconducting circuits connected by optical fibers will require a highly efficient and low-noise microwave-to-optical transducer. We have developed such a transducer by simultaneously coupling a mechanical mode of a Si₃N₄ membrane to a superconducting LC circuit and a high finesse optical Fabry-Perot cavity. In the presence of strong parametric pumps, we have operated the transducer with 47% efficiency and 3.2 photons of input referred added noise [1]. Quantum operation requires further reduction of the noise, which is currently dominated by noise induced by the strong microwave pump. We observe that the induced microwave noise is positively correlated with excess microwave loss, which is strongly dependent on circulating power and temperature of the LC circuit. We have narrowed down the source of the excess loss to the Si₃N₄. Here, we present efforts to reduce the loss and noise through thermal treatment and geometrical screening of the dielectric.



[1] Brubaker, B. M., Kindem, J. M., Urmey, M.D, et. al., Optomechanical Ground-State Cooling in a Continuous and Efficient Electro-Optic Transducer, Phys. Rev. X 12, 021062