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arXiv:1007.0869 · Physical Review A

Narrowband-biphoton generation due to long-lived coherent population oscillations

A. V. Sharypov, A. D. Wilson‐Gordon

Published Sep 21, 2011• 8 citations
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Abstract

We study the generation of paired photons due to the effect of four-wave mixing in an ensemble of pumped two-level systems that decay via an intermediate metastable state. The slow population relaxation of the metastable state creates long-lived coherent population oscillations, leading to a narrowband nonlinear response of the medium which determines the narrow spectral width and long coherence time of the biphotons.

DOI
10.1103/physreva.84.033845

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The generation of nonclassical photon pairs with a long coherence time is key for applications that range from fundamental to quantum communication and metrology. Spontaneous four-wave mixing with electromagnetically induced transparency has been demonstrated as one of the most efficient methods; however, narrowing the bandwidth and producing photon pairs with a temporal length beyond 1 μs remains a technical challenge due to noise considerations and the need for cold atoms with a high optical depth (OD). In this work, we demonstrate the generation of narrowband photon pairs with a controllable coherence time up to 1.72 μs in a laser-cooled atomic ensemble with an OD as high as 130. At such a high OD, we find that the pump laser field spatial profile has a significant effect on the time–frequency entangled two-photon waveform. We also confirm the quantum particle nature of heralded narrowband single photons generated from this source.