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Recent progress in single-photon and entangled-photon generation and applications

Quantum information science has recently attracted a lot of attention. Its applications include secure communication, quantum computation, quantum simulation, and quantum metrology. In these applications, photons are one of the most important physical quanta for their tolerance to decoherence. In this manuscript, we review the recent progress in single-photon/entangled-photon emitters and their applications: heralded single-photon sources using parametric downconversion and their application to quantum key distribution, highly indistinguishable heralded single-photon sources, fiber-coupled solid-state single-photon sources, and ultrabroadband-frequency entanglement generation.