Exceptional points enhance sensing in silicon micromechanical resonators

Exceptional points (EPs) have recently emerged as a new method for engineering the response of open physical systems, that is, systems that interact with the environment. The systems at the EPs exhibit a strong response to a small perturbation. Here, we show a method by which the sensitivity of silicon resonant sensors can be enhanced when operated at EPs. In our experiments, we use a pair of mechanically coupled silicon micromechanical resonators constituting a parity-time (PT)-symmetric dimer. Small perturbations introduced on the mechanically coupled spring cause the frequency to split from the EPs into the PT-symmetric regime without broadening the two spectrum linewidths, and this frequency splitting scales with the square root of the perturbation strength. The overall signal-to-noise ratio is still greatly enhanced, although the measured noise spectral density of the EP sensing scheme has a slight increase comparable to the traditional counterpart. Our results pave the way for resonant sensors with ultrahigh sensitivity.