例外点（EPs）最早源于非厄米物理，能够显著放大系统对微小扰动的响应，并作为增强计量测量的一种有用概念。特别是，这种计量增强会随例外点阶数的增加而急剧增长。然而，非厄米系统中固有的朗之万噪声会削弱这种增强。在本研究中，我们提出了一种量子计量方案，通过厄米磁子-光子相互作用在原子-腔系统中构造高阶例外点（HOEPs）。高阶例外点的构造利用了原子-腔类非厄米动力学行为，同时通过厄米相互作用避免了外部朗之万噪声。我们给出了一般性分析，用于构造任意 n 阶例外点（EPn）。为展示这些高阶例外点在量子计量中的优越性，我们设计了一种基于 EP3/4 的原子传感器，其灵敏度比基于 EP2 的原子传感器可达到的灵敏度高出数个数量级。我们进一步揭示了高阶例外点带来灵敏度增强的机制。针对该方案，我们提出了实验实现建议及潜在候选系统。这种基于例外点的原子传感器利用了原子-光界面，为利用高阶例外点进行量子计量提供了新的见解。
英文摘要：
Exceptional points (EPs), which arose early from non-Hermitian physics, significantly amplify the system's response to minor perturbations, and they act as a useful concept to enhance measurement in metrology. In particular, such a metrological enhancement grows dramatically with the EP's order. However, the Langevin noises intrinsically existing in the non-Hermitian systems diminish this enhancement. In this study, we propose a protocol for quantum metrology with the construction of higher-order EPs (HOEPs) in an atom-cavity system through Hermitian magnon-photon interaction. The construction of HOEPs utilizes the atom-cavity non-Hermitian-like dynamical behavior but avoids the external Langevin noises via the Hermitian interaction. A general analysis is exhibited for the construction of arbitrary -order EP (EPn). As a demonstration of the superiority of these HOEPs in quantum metrology, we work out an EP3/4-based atomic sensor with sensitivity being orders of magnitude higher than that achievable in an EP2-based atomic sensor. We further unveil the mechanism behind the sensitivity enhancement from HOEPs. The experimental establishment for this proposal is suggested with potential candidates. This EP-based atomic sensor, taking advantage of the atom-light interface, offers new insight into quantum metrology with HOEPs.
Universal quantum Fisher information and simultaneous occurrence of Landau-class and topological-class transitions in non-Hermitian Jaynes-Cummings models
