量子存储器作为构建量子网络的核心器件，近十几年来发展迅速。在量子计算中，它可用作不同信息处理过程间的同步装置。在量子通信中，可结合纠缠交换技术实现量子中继，使远距离量子通信成为可能。其中固态量子存储器具有存储寿命长，带宽大，保真度高，多模式存储能力强等优点，是最有希望实现量子中继的量子存储系统之一。除此之外，作为光与物质的相互作用系统，量子存储器及其对应量子光源还可进行有关基本量子物理问题的研究，如光子反常轨迹的观测和宏观实在性的检验等。 本人博士期间主要进行基于掺Nd晶体的宽带固态量子存储器的研究，包括一些其在量子通信以及量子基本问题检验方面的应用。本文所取得的主要研究成果如下： 1.对¹⁴³Nd:YVO₄晶体的光谱及存储性质的应用研究。 基于Nd-143的稀土掺杂晶体由于其内部存在的核自旋能级，使其有望在未来实现长寿命量子存储。我们首次在同位素提纯¹⁴³Nd:YVO₄晶体中实现了初步的光谱学研究，并进一步实现了原子频率梳的制备和二能级原子频率梳存储。这些研究为下一步光子在该体系中进入核自旋能级实现自旋波量子存储提供可行性。 2.提出基于中等寿命量子存储器的半分层型量子中继理论方案。 大尺度量子网络的构建依赖于实用化量子存储器的实现。目前，已经存在很多量子中继方案，其基本目标是要超越光纤直接传输单光子。然而其中绝大多数方案都存在光子分配效率不高以及利用现有技术难以实现等不足。我们提出一种半分层型的量子中继结构，它能在优化分配速率的同时将存储器的寿命需求降至数十毫秒量级。同时该方案还能固定节点的距离，此时中继器对存储器的寿命需求也就固定，几乎与分配距离无关，这种配置适用于大规模量子网络中需要可拓展应用的场景。 3.实验观察到单光子的反常历史轨迹。 当我们考虑一个光子的运动轨迹的时候，量子力学给出的解释与经典世界的现象之间的矛盾变得异常突出。从经典的角度来看，轨迹只有对粒子才有意义，对波来说并不适用。而波粒二象性的发现使得这种二分法的概念逐渐被人们所抛弃，取而代之的是量子力学给出的出色解决办法：轨迹可以被严格定义，但是它与经典的轨迹概念全然不同。通过利用单光子的频谱组成来标记其路径的技术，我们给出了单光子轨迹的一种操作性定义，该定义显示利用光的频率自由度可以构建一种真正的量子测量设备。利用这种方法，我们分析了一系列装置，发现了反常不连续的光子轨迹，从光子产生的地方到其探测的地方之间并不连接。利用级联的干涉仪，我们在实验上展示了这些不连续的光子轨迹，并进一步演示了如何利用二态波矢法对实验结果进行简单解释。 4.在光与物质相互作用的系统中实现了对宏观实在性的严格实验检验。 宏观实在性是一种经典的世界观，它认为一个宏观系统总是会确定地处于一系列宏观可区分的状态中的一个，因而不可能处于这些状态的叠加之中。在宏观尺度上的量子现象是否存在物理基本原理的限制，这个问题至今仍然不清楚。实验上，我们利用量子存储器在光与物质相互作用界面实现了一个严格而简单的宏观实在性检验。我们首先产生一个包含两个宏观可区分固态系统激发态的微观-宏观纠缠态。通过实验检验，我们证明了在该体系中由10¹⁰个离子共享的涉及76个原子激发的相干叠加态依然违背宏观实在性。这些结果为利用量子存储技术提高原子叠加态的尺度以及进一步推进划分微观与宏观的界限提供了一种通用的方法。 关键词：固态量子存储，量子中继，稀土掺杂晶体，量子光源，自发参量下转换，反常历史轨迹，宏观实在性

 As the key components for building quantum networks, quantum memory has developed rapidly in the past decade. In quantum computing, it can be used as a synchronization tool that matches various process within a quantum computer. In quantum communication, it can be used to realize quantum repeater combining with entanglement swapping technique, enabling quantum communication over long-distance. The solid-state quantum memory has the advantages of long lifetime, large bandwidth, high fidelity and high multimode capability, which make it become one of the most prominent candidates for realizing quantum repeater. In addition, as a light-matter interfaced system, quantum memory and its matching single-photon source can also be utilized to perform research on some fundamental quantum physics problems, such as the observation of anomalous trajectories of single photons and tests of macroscopic realism. During my PhD, I mainly focus on the study of wideband solid-state quantum memory based on Nd-doped crystals, including its application in quantum communication and tests of fundamental quantum physics. The followings are the main research works of my doctoral dissertation: 1.Spectroscopic investigations of ¹⁴³Nd:YVO₄ for quantum memory applications. Because of the stable nuclear spin energy levels, Nd-143 ions doped crystal can be considered as a promising candidate system for realizing long-lived quantum memory in the future. For the first time, we performed basic spectroscopic investigations in isotope pure ¹⁴³Nd:YVO₄ crystals. Furthermore, we achieved the preparation of the atomic frequency comb (AFC) and implemented the two-level AFC quantum storage. These studies provide feasibility for the realization of spin-wave quantum memory if we can transfer optical excitations into ground-state spin levels in this system. 2.Semihierarchical quantum repeaters based on moderate lifetime quantum memories. The construction of large-scale quantum networks relies on the development of practical quantum repeaters. Many approaches have been proposed with the goal of outperforming the direct transmission of photons, but most of them are inefficient or difficult to implement with current technology. Here, we present a protocol that uses a semihierarchical structure to improve the entanglement distribution rate while reducing the requirement of memory time to a range of tens of milliseconds. This protocol can be implemented with a fixed distance of elementary links and fixed requirements on quantum memories, which are independent of the total distance. This configuration is especially suitable for scalable applications in large-scale quantum networks. 3.Experimental observation of anomalous trajectories of single photons. The contradiction between quantum mechanics and classical world become especially sharp in case one consider trajectories of truly quantum objects such as single photons. From a classical point of view, trajectories are well defined for particles, but not for waves. The wave-particle duality forces a breakdown of this dichotomy and quantum mechanics resolves this in a remarkable way: Trajectories can be well defined, but they are utterly different from classical trajectories. We give an operational definition to the trajectory of a single photon by introducing a technique to mark its path using its spectral composition. The method demonstrates that the frequency degree of freedom can be used as a bona fide quantum measurement device (meter). The analysis of a number of setups, using our operational definition, leads to anomalous trajectories which are noncontinuous and in some cases do not even connect the source of the photon to where it is detected. We carried out an experimental demonstration of these anomalous trajectories using a nested interferometer. We show that the two-state vector formalism provides a simple explanation for the results. 4.Strict experimental test of macroscopic realism in a light-matter interfaced system. Macroscopic realism is a classical worldview that a macroscopic system is always determinately in one or other of the macroscopically distinguishable states available to it, and so is never in a superposition of these states. The question that whether there is a fundamental limitation on the possibility to observe quantum phenomena at the macroscopic scale remains unclear. We implement a strict and simple protocol to test macroscopic realism in a light-matter interfaced system. We create a micro-macro entanglement with two macroscopically distinguishable solid-state components and rule out those theories which would deny coherent superpositions of up to 76 atomic excitations shared by 10¹⁰ ions in two separated solids. These results provide a general method to enhance the size of superposition states of atoms by utilizing quantum memory techniques and to push the envelope of macroscopicity at higher levels. Keywords: Solid-state quantum memory, Quantum repeater, Rare-earth doped crystal, Quantum light source, Spontaneous parametric down-conversion, Anomalous trajectory, Macroscopic realism