Sublinear Sensors with Enhanced Signal-to-Noise Ratio

The enhanced wave-matter interactions occurring at the exceptional point degeneracies (EPDs) of the resonant spectrum of non-Hermitian systems has inspired a whole new class of hypersensitive sensors. The main feature of these sensors was their enhanced signal due to a sublinear resonant detuning from the EPD, occurring when a perturbing agent was interacting with the sensor. The initial excitement for these developments has been followed by a skepticism associated with the observation that in some lasing platforms the enhanced measured signal is accompanied by an equally enhanced noise. The excess noise can be of fundamental nature (owing to the eigenbasis collapse) or of technical nature associated with the amplification mechanisms utilized for the realization of EPDs. Here, we proposed another EPD scheme based on the lasing modes of a parity-time symmetric electromechanical system with an additional saturable lossy nonlinearity. We show that in the appropriate parameter range, the system has two stable lasing modes which form a EPD at a critical value of the coupling between the gain and loss resonators of the system. A subsequent noise analysis indicates that nonlinearities suppress the noise leading to an order of magnitude enhancement of the signal-to-noise ration in the proximity of the EPD. The experimental results are nicely supported by a theoretical analysis.