Exceptional precision of a nonlinear optical sensor at a square-root singularity

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Reference K.J.H. Peters and S.R.K. Rodriguez, Exceptional precision of a nonlinear optical sensor at a square-root singularity, Phys.Rev.Lett. 129, 013901: 1-7 (2022)
Group Interacting Photons

Exceptional points (EPs) — spectral singularities of non-Hermitian linear systems — have recently attracted interest for sensing. While initial proposals and experiments focused on enhanced sensitivities neglecting noise, subsequent studies revealed issues with EP sensors in noisy environments. Here we propose a single-mode Kerr-nonlinear resonator for exceptional sensing in noisy environments. Based on the resonator’s dynamic hysteresis, we define a signal that displays a square-root singularity reminiscent of an EP. However, our sensor has crucial fundamental and practical advantages over EP sensors: the signal-to-noise ratio increases with the measurement speed, the square-root singularity is easily detected through intensity measurements, and both sensing precision and information content of the signal are enhanced around the singularity. Our sensor also overcomes the fundamental trade-off between precision and averaging time characterizing all linear sensors. All these unconventional features open up new opportunities for fast and precise sensing using hysteretic resonators.