Departments of Applied Physics and Physics, Yale University, New Haven, Connecticut 06520, USA.
Yale Quantum Institute, Yale University, New Haven, Connecticut 06520, USA.
Phys Rev Lett. 2019 Nov 1;123(18):180501. doi: 10.1103/PhysRevLett.123.180501.
Open quantum systems can have exceptional points (EPs), degeneracies where both eigenvalues and eigenvectors coalesce. Recently, it has been proposed and demonstrated that EPs can enhance the performance of sensors in terms of amplification of a detected signal. However, typically amplification of signals also increases the system noise, and it has not yet been shown that an EP sensor can have improved signal-to-noise performance. We develop a quantum noise theory to calculate the signal-to-noise performance of an EP sensor. We use the quantum Fisher information to extract a lower bound for the signal-to-noise ratio (SNR) and show that parametrically improved SNR is possible. Finally, we construct a specific experimental protocol for sensing using an EP amplifier near its lasing threshold and heterodyne signal detection that achieves the optimal scaling predicted by the Fisher bound. Our results can be generalized to higher order EPs for any bosonic non-Hermitian system with linear interactions.
开放量子系统可以具有临界点 (EP)，即本征值和本征向量合并的简并。最近，有人提出并证明，EP 可以增强传感器的性能，例如放大检测到的信号。然而，通常情况下信号的放大也会增加系统噪声，并且尚未表明 EP 传感器可以具有改善的信噪比性能。我们开发了一种量子噪声理论来计算 EP 传感器的信噪比性能。我们使用量子 Fisher 信息来提取信噪比的下界，并表明参数化提高 SNR 是可能的。最后，我们构建了一个使用 EP 放大器在其激光阈值附近进行感应的具体实验方案，并使用外差信号检测来实现 Fisher 边界预测的最佳比例。我们的结果可以推广到任何具有线性相互作用的玻色非厄米系统的更高阶 EP。
