Approaching the single-photon strong coupling regime of optomechanics using a Cooper pair transistor

We report experimental progress on the hybrid optomechanical system described in [1]. The system consists of a coplanar waveguide superconducting microwave cavity whose coupling to a double-clamped beam nanomechanical resonator (NR) is mediated by a Cooper pair transistor (CPT). The optomechanical coupling is no longer purely capacitive, but arises because of the NR-gate induced variation of the quantum inductance of the CPT. This variation increases as we approach charge degeneracy of the CPT and should put us within reach of the single photon strong coupling regime. The band structure of the CPT also introduces other nonlinear terms in the Hamiltonian that should be strong even at low cavity occupation numbers. We can selectively address these by driving at appropriate frequencies and they will be used to generate and readout quantum states in the NR.

[1] A. J. Rimberg, M. P. Blencowe, A. D. Armour, P. D. Nation, New J. Phys. 16, 055008