Clarification of exceptional point contribution for photonic sensing

TL;DR

This paper clarifies that exceptional points in photonic systems do not inherently enhance sensing performance, but can do so when combined with lasing threshold conditions, resolving ongoing debates about their true sensing advantage.

Contribution

The study demonstrates that exceptional points are linked to lasing thresholds rather than directly providing sensing benefits, clarifying their role in photonic sensing.

Findings

Quantum Fisher information divergence is due to lasing threshold, not exceptional points.

Exceptional points occur at lasing threshold across multiple modes.

Exceptional points can enhance sensitivity when combined with lasing threshold.

Abstract

Exceptional points, with simultaneous coalescence of eigen-values and eigen-vectors, can be realized with non-Hermitian photonic systems. With the enhanced response, exceptional points have been proposed to improve the performance of photonic sensing. Recently, there are intense debate about the actual sensing advantage of exceptional points. The major concern is that intrinsic noise is also amplified at exceptional points. Here, we aim to clarify the contribution of exceptional points for photonic sensing. This is achieved by analyzing the condition to realize divergent quantum Fisher information in linear non-Hermitian photonic systems. We show that the divergence of quantum Fisher information is the result of lasing threshold, instead of exceptional points. However, exceptional points correspond to the condition that lasing threshold is simultaneously achieved across multiple photonic modes. Therefore, exceptional points can further improve the sensitivity on top of lasing threshold. On the other hand, exceptional points alone cannot provide sensing advantage.