Abstract Quantum networks play an extremely important role in quantum information science, with application to quantum communication, computation, metrology, and fundamental tests. One of the key challenges for implementing a quantum network is to distribute entangled flying qubits to spatially separated nodes, at which quantum interfaces or transducers map the entanglement onto stationary qubits. The stationary qubits at the separated nodes constitute quantum memories realized in matter while the flying qubits constitute quantum channels realized in photons. Dedicated efforts around the world for more than 20 years have resulted in both major theoretical and experimental progress toward entangling quantum nodes and ultimately building a global quantum network. Here, the development of quantum networks and the experimental progress over the past two decades leading to the current state of the art for generating entanglement of quantum nodes based on various physical systems such as single atoms, cold atomic ensembles, trapped ions, diamonds with nitrogen‐vacancy centers, and solid‐state host doped with rare‐earth ions are reviewed. Along the way, the merits are discussed and the potential of each of these systems toward realizing a quantum network is compared.
Abstract Quantum networks play an extremely important role in quantum information science, with application to quantum communication, computation, metrology, and fundamental tests. One of the key challenges for implementing a quantum network is to distribute entangled flying qubits to spatially separated nodes, at which quantum interfaces or transducers map the entanglement onto stationary qubits. The stationary qubits at the separated nodes constitute quantum memories realized in matter while the flying qubits constitute quantum channels realized in photons. Dedicated efforts around the world for more than 20 years have resulted in both major theoretical and experimental progress toward entangling quantum nodes and ultimately building a global quantum network. Here, the development of quantum networks and the experimental progress over the past two decades leading to the current state of the art for generating entanglement of quantum nodes based on various physical systems such as single atoms, cold atomic ensembles, trapped ions, diamonds with nitrogen‐vacancy centers, and solid‐state host doped with rare‐earth ions are reviewed. Along the way, the merits are discussed and the potential of each of these systems toward realizing a quantum network is compared.
Summary form only given. Entanglement - the property that particles can share a single quantum state - is arguably the most counterintuitive yet potentially most powerful element of quantum physics. Future quantum networks may harness the unique features of entanglement in a range of exciting applications, such as quantum computation and simulation, secure communication, enhanced metrology for astronomy and time-keeping as well as fundamental tests of nature. To fulfill these promises, a strong worldwide effort is ongoing to gain precise control over multi-particle nodes and to wire them up using quantum-photonic channels. Diamond spins associated with NV centers are promising building blocks for such a network as they combine a coherent electron-optical interface [1] (similar to that of trapped atomic qubits) with a local register of robust and well-controlled nuclear spin qubits [2]. Here I will introduce the field of quantum networks and present an overview of the latest progress, including the first loophole-free violation of Bell's inequalities [3,4] and the first primitive network experiments on a pair of spatially separated two-qubit nodes.
Quantum memory, which maps photonic quantum information into a stationary medium and retrieves it at a chosen time, plays a vital role in the advancement of quantum information science. In particular, the scalability of a quantum memory is a central challenge for quantum network that can be overcome by using integrated devices. Quantum memory with an integrated device is highly appealing since it not only expands the number of memories to increase data rates, but also offers seamless compatibility with other on-chip devices and existing fiber network, enabling scalable and convenient applications. Over the past few decades, substantial efforts have been dedicated to achieving integrated quantum memory using rare earth ions doped solid-state materials, color centers, and atomic gases. These physical platforms are the primary candidates for such devices, where remarkable advantages have been demonstrated in achieving high-performance integrated quantum memory, paving the way for efficiently establishing robust and scalable quantum network with integrated quantum devices. In this paper, we aim to provide a comprehensive review of integrated quantum memory, encompassing its background and significance, advancement with bulky memory system, fabrication of integrated device, and its memory function considering various performance metrics. Additionally, we will address the challenges associated with integrated quantum memory and explore its potential applications. By analyzing the current state of the field, this review will make a valuable contribution by offering illustrative examples and providing helpful guidance for future achievements in practical integrated quantum memory.
Entanglement distribution is a fundamental building block of quantum communication networks, enabling the secure and reliable exchange of quantum information over long distances. Unlike classical communication, quantum networks exploit the unique properties of quantum entanglement to support applications such as quantum key distribution, quantum teleportation, distributed quantum computing, and networked quantum sensing. Although significant progress has been made in recent years, the efficient generation, transmission, and preservation of entangled states remain major research challenges due to photon loss, decoherence, and limitations in current communication infrastructure.This review provides a comprehensive overview of entanglement distribution in quantum communication networks, focusing on the technologies that enable practical implementation and the latest experimental developments. It discusses key approaches for generating and distributing entangled photons through optical fibers, free-space links, and satellite-based communication, together with supporting technologies such as quantum repeaters, quantum memories, and photonic devices. The review also examines recent experimental demonstrations that have advanced long-distance quantum communication while highlighting the technical barriers that must be overcome for large-scale deployment. Finally, emerging applications and future research directions are presented, including the development of scalable quantum networks, the quantum internet, and secure global communication systems. This review aims to provide researchers and students with a clear understanding of the current state of entanglement distribution and its growing role in next-generation quantum communication technologies.
Abstract Worldwide, enormous efforts are directed toward the development of the so‐called quantum internet. Turning this long‐sought‐after dream into reality is a great challenge that will require breakthroughs in quantum communication and computing. To establish a global, quantum‐secured communication infrastructure, photonic quantum technologies will doubtlessly play a major role, by providing and interfacing essential quantum resources, for example, flying‐ and stationary qubits or quantum memories. Over the last decade, significant progress has been made in the engineering of on‐demand quantum light sources based on semiconductor quantum dots, which enable the generation of close‐to‐ideal single‐ and entangled‐photon states, useful for applications in quantum information processing. This review focuses on implementations of, and building blocks for, quantum communication using quantum‐light sources based on epitaxial semiconductor quantum dots. After reviewing the main notions of quantum communication and introducing the devices used for single‐photon and entangled‐photon generation, an overview of experimental implementations of quantum key distribution protocols using quantum dot based quantum light sources is provided. Furthermore, recent progress toward quantum‐secured communication networks as well as building blocks thereof is summarized. The article closes with an outlook, discussing future perspectives in the field and identifying the main challenges to be solved.
Distributed quantum computing requires a quantum network with robust links between physically separated quantum nodes [1]. Hybrid networks where nodes from different types of stationary qubits (such as neutral atoms or solid state defects) are linked, can be used to take advantage of the strengths of various systems. An efficient interface for fast and reliable exchange of quantum information between stationary qubits at nodes with photons, or traveling qubits, is needed for distributing entanglement between nodes. A high rate of generating and distributing light-matter entangled states will scale up the speed of computation distributed between the nodes of a network.
Abstract Quantum network is constituted by quantum channels and quantum nodes. The interaction between non‐classical optical modes and quantum nodes, as well as quantum entanglement among multiple distant quantum nodes are the building blocks of quantum network, which enable to achieve a plethora of quantum information protocols, such as distributed quantum computation, quantum state transfer across quantum nodes, and quantum clock network. On one hand, the multipartite non‐classical states of optical modes, which can directly interact with atomic ensembles, are required for the practical applications of quantum network. On the other hand, a crucial goal of quantum network is to unconditionally generate and on‐demand store and retrieve multipartite entangled states in atomic ensembles. This paper presents an up‐to‐date review on recent developments in these areas: multipartite continuous‐variable polarization entangled optical modes have been created by transforming quantum state from quadrature into polarization components; and a scalable quantum network with deterministic entanglement among multiple quantum memories has been constructed by transferring spatially separated entangled optical modes into atomic ensembles.