基于弱场零差结构的量子探测器的响应机制和量子功能研究

Weak-field homodyne detector as a new quantum detector structure provides simultaneous sensitivity to both the particle behavior and wave behavior of light field. Such kind of hybrid quantum detectors are beginning to play key roles in investigating fundamental quantum phenomena, generating exotic quantum states, and form essential resources for quantum-enhanced applications, e.g. entanglement distillation and quantum computation, as well as highly efficient optical telecommunications. Therefore a complete study of the response and quantum utility of weak-field homodyne detectors will not only help us to design more powerful quantum detector structures to improve the performance of quantum-optical applications, but also shed new light on the study of one of the fundamental theories of quantum mechanics, the measurement theory. We have for the first time experimentally characterized the fundamental structure of the weak-field homodyne detector through quantum detector tomography. Compared to the classical characterization of photodetectors using parameters such as detectivity, spectral sensitivity and noise equivalent power, detector tomography provides a direct, complete, and assumption-free specification of quantum detectors via its operator (called Positive-Operator-Valued Measure, or POVM), which links the quantum input states to the classical detector output. As an example, our experiment reveals the non-classical nature within the weak-field homodyne detector. Being the first tomography of phase-sensitive quantum detectors, these results provide a universal, device-independent understanding of the role of quantum coherence in a measurement process. Therefore our scheme underpins the study of the quantum utility of a quantum-optical detector. In this project, we will establish a complete theoretical model based on the previous experimental results to describe the behavior of the weak-field homodyne detector. The model will take into account the coupling to the external degrees of freedom to highlight the effect of decoherence on the quantum utility of the detector. We will extend this model to more complicated structures, e.g. with multiple receiving ports, multiple local oscillators and even with feedbacks. To test and complement the theoretical study, we will improve the current detector tomography scheme for the experimental investigation of extended structures of the weak-field homodyne detector. We will further develop novel tools to quantify the 'quantum detectivity', e.g. the precision of measuring certain parameters, the capability of distinguishing certain states, of weak-field homodyne detectors through their POVM operators, and study the applications of such detectors in quantum metrology, quantum and classical communications. The proposed work will not only design and develop novel quantum-optical detector structures and applications, but also try to build a toolbox for benchmarking the quantum utility of detectors.

弱场零差探测器（weak-field homodyne detector）可以同时探测入射信号的粒子行为和波动行为，因而逐渐开始在各种量子技术和量子力学基本理论的研究中发挥重要作用。全面理解其响应机制和量子功能，不但对于设计更为复杂和强大的量子探测器有着重要意义，对于我们理解量子力学核心问题之一的测量问题也有着启发意义。申请人在国际上首次通过探测器层析的方法对弱场零差探测器的基本结构进行了实验研究，对其响应机制和非经典特性有了初步理解。本项目将建立关于该探测器工作原理的完备理论模型，进一步拓展探测器结构；改进现有的探测器层析方案，对新的探测器结构进行实验研究；开发新的理论和实验工具来定量地研究不同结构的测量精度和分辨率，以及在各种量子技术中的应用。本项目在开发新的探测系统结构以及基于这些结构的量子技术的同时，还将完善现有的量子探测器研究的理论体系，建立探测器量子功能的研究基准。

量子探测器是光量子技术的核心组成部分之一，在量子通信、量子计算、量子精密测量等方面发挥着重要的作用。相比起量子光源，关于量子量子探测器的研究相对匮乏。近年来，一种新型的量子探测器，弱场零差探测器，逐渐受到更多关注。该探测器可以同时探测入射信号的 粒子行为和波动行为，因而在各种量子技术和量子力学基本理论的研究中发挥重要作用。全面理解其响应机制和量子功能，不但对于设计更为复杂和强大的量子探测器有着重要要意义，对于我们理解量子力学核心问题之一的测量问题也有着启发意义。本项目针对该探测器展开研究，建立了该探测器工作原理的完备理论模型并进行了实验验证，进而对该探测器中的相干性进行了量化。.项目的主要研究成果包括一下几个方面：1、在原理论模型中加入了探测噪声、干涉对比度等实际因素，完善了探测器模型；2、完善了量子探测器层析的算法，并提出了量子探测器层析中的误差分析方法，给出了层析结果的置信区间；3、利用新算法，完成了弱场零差探测器的层析实验；4、利用量子资源理论，完善了量子探测系统相干性的理论体系，并对弱场零差探测器的相干性进行了标定。本项目在开发新的探测系统结构以及基于这些结构的量子技术的同时，完善了现有的量子探测器研究的理论体系，建立探测器量子功能的研究基准。