标题： 在基本量子极限下的贝叶斯频率估计 显示英文标题

标题： Bayesian frequency estimation at the fundamental quantum limit

摘要： 在未知频率处搜索微弱信号是探测基础物理实验中的一个经典任务，例如引力波观测站和超轻暗物质晕探测器。 这些最先进的传感器受到量子噪声的限制，这种噪声源于对设备状态的基本不确定性。 经典上，频率估计在信噪比方面存在阈值效应，使得微弱信号在频率上极难定位。 我们表明，这种现象在基本量子极限下仍然存在，但经典的正交测量方法可以通过对“量子白化”可能的量子态进行投影的相干协议来超越。 量子白化是一种协变测量，在宽先验极限下我们对其进行分析，并针对有限宽度先验进行数值研究。 除了加速对未知频率的搜索外，量子白化可以普遍用于在没有任何参数先验信息的情况下感知单位编码的参数。 显示英文摘要

摘要： Searching for a weak signal at an unknown frequency is a canonical task in experiments probing fundamental physics such as gravitational-wave observatories and ultra-light dark matter haloscopes. These state-of-the-art sensors are limited by quantum noise arising from the fundamental uncertainty about the state of the device. Classically, frequency estimation suffers from a threshold effect in the signal-to-noise ratio such that weak signals are extremely hard to localise in frequency. We show that this phenomenon persists at the fundamental quantum limit but that the classical approach, a quadrature measurement, can nevertheless be beaten by a coherent protocol of projecting onto the "quantum whitened" possible quantum states. Quantum whitening is a covariant measurement, and we examine it analytically in the wide-prior limit and numerically for finite-width priors. Beyond accelerating searches for unknown frequencies, quantum whitening may be used generally to sense the parameter of a unitary encoding given no prior information about the parameter.