Fluorescence antibunching from single terrylene molecules embedded in a cholesteric-liquid-crystal host is used to demonstrate operation of a room-temperature single-photon source. One-dimensional (1-D) photonicband-gap microcavities in planar-aligned cholesteric liquid crystals with band gaps from visible to near-infrared spectral regions are fabricated. Liquid-crystal hosts (including liquid crystal oligomers and polymers) increase the source efficiency, firstly, by aligning the dye molecules along the direction preferable for maximum excitation efficiency (deterministic molecular alignment provides deterministically polarized output photons), secondly, by tuning the 1-D photonic-band-gap microcavity to the dye fluorescence band and thirdly, by protecting the dye molecules from quenchers, such as oxygen. In our present experiments, using oxygen-depleted liquid-crystal hosts, dye bleaching is avoided for periods exceeding one hour of continuous 532 nm excitation. IntroductionA single-photon source (SPS) [1, 2] that efficiently produces photons with antibunching characteristics [3] is a pivotal hardware element for quantum communication technology [4][5][6]. Using a SPS, secure quantum communication will prevent any potential eavesdropper from intercepting a message with a secure key without the receiver noticing [4]. Quantum communication has a potential large market [7,8], but its practical realization is held back in part because of the difficulties in developing robust sources of antibunched photons on demand. In another implementation, a SPS becomes the key hardware element for quantum computers with linear optical elements and photodetectors [9][10][11][12].In spite of several solutions for SPSs presented in the literature, significant drawbacks remain. They are the reason why current quantum communication systems are baud-rate bottlenecked, causing photon numbers from ordinary photon sources to attenuate to the single-photon level (approximately 0.1 photon per pulse

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