Enhanced Whispering Gallery Mode Phase Shift using Indistinguishable Photon Pairs

We present a theoretical investigation of a whispering gallery mode (WGM) resonator coupled to a Mach-Zehnder interferometer (MZI) and show a bimodal coincidence transmission spectrum when the input state is an indistinguishable photon pair. This is due to the doubled WGM phase shift experienced by the path-entangled state in the interferometer. Further, we model the noise in a WGM resonance shift measurement comparing photon pairs with a coherent state. At least a four-fold improvement in the signal-to-noise ratio (SNR) is possible, with clear implications for quantum-enhanced WGM sensing.