Towards Real-World Quantum Networks: A Review

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.

Automated summary

Quantum networks are crucial for quantum information science, enabling applications in quantum communication, computation, metrology, and fundamental tests. The main challenge lies in distributing entangled flying qubits to separate nodes, where quantum interfaces or transducers map the entanglement onto fixed qubits. Extensive efforts over the past two decades have led to significant progress in entangling quantum nodes and building a global quantum network using various physical systems. This review discusses the development of quantum networks and experimental advancements, comparing the potential and merits of systems such as single atoms, cold atomic ensembles, trapped ions, diamonds with nitrogen-vacancy centers, and solid-state hosts doped with rare-earth ions.