Limitations of Sensing at an Exceptional Point

With the rapid progress of high-quality superconducting and photonic resonators, it has become possible to sense with extremely high precision a wide range of physical properties. Along with these advances, several proposals have recently been put forward for schemes that maximize the sensitivity of these sensing systems. Of particular recent interest are sensors operating near exceptional points (EPs), which have been shown to provide dramatic variations of their eigenvalues in response to small parameter changes. While there have been theoretical and experimental reports of sensitivity enhancements under these operating conditions, recent work has also cast doubts around the actual benefit of operating near an EP for sensors under realistic conditions. In this paper, we study the fundamentals of sensing in linear scattering systems operating near an EP, analyzing the specific role of EPs and of the associated amplification mechanisms; we specifically show that eigenvalue variations under a perturbation are not a good measure of the overall sensor performance near an EP. Further, we note that sensors with amplification should account for the extra energy usage when comparing to passive sensors.