标题： 量子光最优圆二色性传感：多参数估计方法 显示英文标题

标题： Optimal circular dichroism sensing with quantum light: Multi-parameter estimation approach

摘要： 圆二色性（CD）的测量被广泛用于区分手性结构的不同对映异构体。 它已被应用于天然材料（例如分子）以及人工材料（例如纳米光子结构）。 然而，特别是对于手性分子，信号水平非常低，提高信噪比对于缩短必要的测量时间或降低最低可检测分子浓度至关重要。 作为解决此问题的一种方案，我们提出在此使用光的量子态进行CD传感，以将噪声降低到使用相干态光时遇到的散粒噪声极限以下。 通过多参数估计方法，我们确定了CD传感精度的终极量子极限，允许包括额外辅助模式的通用方案。 我们表明，可以通过各种最优方案实现终极量子极限。 这不仅包括直接传感配置中的Fock态输入，还包括辅助模式传感配置中的双光束输入，对于这两种情况都需要进行光子数分辨探测作为最优测量设置。 即使存在额外的系统损耗，这些最优方案也能提供显著的量子增强。 还详细研究了在直接传感配置中使用双光束态的实际方案的最优性，作为实际CD信号非常小时CD传感的近似最优方案。 还提出了涉及单光子源和探测器的替代方案。 这项工作为进一步研究量子计量技术在手性传感中的应用铺平了道路。 显示英文摘要

摘要： The measurement of circular dichroism (CD) has widely been exploited to distinguish the different enantiomers of chiral structures. It has been applied to natural materials (e.g. molecules) as well as to artificial materials (e.g. nanophotonic structures). However, especially for chiral molecules the signal level is very low and increasing the signal-to-noise ratio is of paramount importance to either shorten the necessary measurement time or to lower the minimum detectable molecule concentration. As one solution to this problem, we propose here to use quantum states of light in CD sensing to reduce the noise below the shot noise limit that is encountered when using coherent states of light. Through a multi-parameter estimation approach, we identify the ultimate quantum limit to precision of CD sensing, allowing for general schemes including additional ancillary modes. We show that the ultimate quantum limit can be achieved by various optimal schemes. It includes not only Fock state input in direct sensing configuration but also twin-beam input in ancilla-assisted sensing configuration, for both of which photon number resolving detection needs to be performed as the optimal measurement setting. These optimal schemes offer a significant quantum enhancement even in the presence of additional system loss. The optimality of a practical scheme using a twin-beam state in direct sensing configuration is also investigated in details as a nearly optimal scheme for CD sensing when the actual CD signal is very small. Alternative schemes involving single-photon sources and detectors are also proposed. This work paves the way for further investigations of quantum metrological techniques in chirality sensing.