Nonreciprocal quantum sensing via directional squeezing in two coupled microring resonators

We propose a scheme for nonreciprocal quantum rotation sensing in two coupled microring resonators, one of which rotates in a clockwise direction. Driving the rotating resonator in two directions induces the opposite Sagnac-Fizeau shifts. By pumping the other nonlinear resonator via classical field, directional squeezing is generated along the pump direction due to the phase-matching condition, which leads to an asymmetric detuning and chiral photon interaction between the two resonators. As a result, the estimation of the Sagnac-Fizeau shift is shown to be nonreciprocal, i.e., the estimation precision is dramatically enhanced for the forward-input case, where most of the accessible information is predominantly stored in the primary resonator, but not for the backward-input one. Further, we evaluate the performance of several Gaussian measurements and analyze how measurements of the second-order coherence g⁽²⁾(0) can extract quantum-enhanced information and improve measurement precision. The proposed scheme offers what we believe to be a new perspective for the design of a nonreciprocal quantum gyroscope.