Enhancing the sensitivity of nonlinearity sensors through homodyne detection in dissipatively coupled systems

In this manuscript, we propose a new sensing mechanism to enhance the sensitivity of a quantum system to nonlinearities by homodyning the amplitude quadrature of the cavity field. The system consists of two dissipatively coupled cavity modes, one of which is subject to single- and two-photon drives. In the regime of low two-photon driving strength, the spectrum of the system acquires a real spectral singularity. We find that this singularity is very sensitive to the two-photon drive and nonlinearity of the system, and compared to the previous nonlinearity sensor, the proposed sensor achieves an unprecedented sensitivity around the singularity point. Moreover, the scheme is robust against fabrication imperfections. This work would open a new avenue for quantum sensors, which could find applications in many fields, such as the precise measurement and quantum metrology.