Exceptional Point Enhances Sensitivity of Optomechanical Mass Sensors

We propose an efficient optomechanical mass sensor operating at exceptional points (EPs), non-Hermitian degeneracies where eigenvalues of a system and their corresponding eigenvectors simultaneously coalesce. The benchmark system consists of two optomechanical cavities that are mechanically coupled, where we engineer mechanical gain (loss) by driving the cavity with a blue-detuned (red-detuned) laser. The system features an EP at the gain and loss balance, where any perturbation induces a frequency splitting that scales as the square root of the perturbation strength, resulting in a giant sensitivity-factor enhancement compared with conventional optomechanical sensors. For nonidentical mechanical resonators, quadratic optomechanical coupling is used to tune the frequency mismatch to get closer to the EP, extending the efficiency of our sensing scheme to mismatched resonators. This work paves the way toward new levels of sensitivity for optomechanical sensors, which could find applications in many other fields, including nanoparticle detection, precision measurement, and quantum metrology.