Rubidium atom makes single-photon server

Quantum-information technology depends on single-photon sources.

Quantum-information technology depends on single-photon sources (see Although by its nature a single neutral atom can generate only one photon at a time, the difficulty in single-photon generation has up to now been the short duration of the emitted stream of photons-too short to adequately use the photons and ensure they are indistinguishable from each other. But by using a cavity-based scheme in which a dipole laser traps a single rubidium (Rb) atom, a trigger laser is used for photon generation, and a recycling laser is used for repumping, monitoring, and cooling the atom, researchers at the Max Planck Institute for Quantum Optics (Garching, Germany) and the University of Oxford (Oxford, England) have developed a single-photon server that delivers up to 300,000 sequential photons for as long as 30 s.

A single Rb atom is trapped in a high-finesse optical cavity by a two-dimensional optical lattice. A weak 785 nm cavity-stabilization laser confines the atom along the cavity axis, while a strong retroreflected-dipole laser confines the atom in a direction perpendicular to the cavity axis. The cavity is excited by a sequence of laser pulses, and a series of mirrors and filters deliver a stream of high-quality single photons. Contact Gerhard Rempe at

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