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Frontiers in Optics

No Fundamental Sensing Advantage from Exceptional Point Sensors

Hudson A. Loughlin, Vivishek Sudhir

Published Jan 1, 2024• 0 citations
Publisher

Abstract

We present a theory of quantum noise in exceptional point sensors. We find that these sensors have no sensing advantage relative to traditional sensors limited by fundamental quantum or thermal noise.
DOI
10.1364/fio.2024.ftu6c.4

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Exceptional-point (EP) sensors exhibit a square-root resonant frequency bifurcation in response to external perturbations, making them appear attractive for sensing applications. However, there is an open debate as to whether or not this sensitivity advantage is negated by additional noise in the system. We settle this debate by showing that increased fundamental noises of quantum and thermal origin in EP sensors, and in particular self-excited (or PT-symmetric) EP sensors, negate the sensitivity benefit. Accordingly, EP sensing schemes are only beneficial either with further quantum enhancement or if compared to sensors limited by technical noise. As many modern sensors are limited by technical noise, EP sensors may still find practical uses despite their lack of a fundamental advantage. Alternatively, we propose a quantum-enhanced EP sensor that achieves a sensing advantage even when limited by quantum or thermal fluctuations.
A fundamental aspect of quantum systems lies in their extreme sensitivity to external perturbations. This characteristic, which generally represents a considerable challenge for physicists seeking to isolate these systems in order to observe their quantum properties, can actually be transformed into an advantage. Indeed, this intrinsic sensitivity makes quantum systems ideal candidates for high-precision metrology. Quantum sensors exploit this susceptibility to measure physical quantities with precision difficult to match with classical approaches.
Abstract Parity-time (PT)-symmetric non-Hermitian systems exhibit a heightened sensitivity to external environmental changes, making them a popular choice in the field of quantum sensing. In this study, we designed a small tilt sensor based on the exceptional point (EP) of non-Hermitian systems. The measurement sensitivity of the sensor can be increased by a factor of 10000 times when compared with that of traditional sensors. However, in terms of the measurement precision of the EP sensor, there was no significant improvement because the EP sensor amplified the signal while amplifying the noise. Nonetheless, EP sensors retain clear advantages in specialized scenarios, such as detector saturation events, during which they surpass traditional sensors. Subsequently, we increased the measurement precision of the EP sensor by 2 n + 1 times by using high-order Hermite-Gaussian (HG) light, where n denotes the mode order of the signal light. Finally, we conclude this study with an analysis of the noise in EP sensors based on quantum error theory. Furthermore, we explore how EP sensors can strike a balance between high sensitivity and precision by incorporating a squeezed light field with elevated HG modes.