Abstract

The interaction of light with a two-level emitter is the most fundamental process in quantum optics and key to many applications in quantum science and technology. One peculiarity is that two photons are never simultaneously detected in the light scattered by a single quantum emitter. This is commonly interpreted to mean that a single two-level quantum emitter can only absorb and emit single photons. Here we show by spectrally filtering the fluorescence of such an emitter, that the remaining light consists of a stream of photon pairs that have been simultaneously scattered by the two-level emitter [1].

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