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arXiv:1609.02378 · Optics Express

Highly bright photon-pair generation in Doppler-broadened ladder-type atomic system

Yoon‐Seok Lee, Sang Min Lee, Heonoh Kim, Han Seb Moon

Published Nov 23, 2016• 62 citations
arXivHTMLPDF

Abstract

Rb. The photon-pair generation rate is enhanced by the two-photon coherence contributions from almost all the atomic velocity groups in the Doppler-broadened ladder-type atomic system. We obtained the violation of the Cauchy-Schwarz inequality by a factor of 2370 ± 150. We believe that our scheme for highly bright paired photons is important as a useful quantum light source for quantum entanglement swapping between completely autonomous sources.

DOI
10.1364/oe.24.028083

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We experimentally demonstrate two-photon interference of a time-energy entangled photon pair generated via collective two-photon coherence in Doppler-broadened cascade-type ^{87}Rb atoms. The two photons originally proposed by J. D. Franson are realized as a photon pair due to collective effects, which are generated from the cascade atomic system with a relatively long lifetime of the initial state and a considerably shorter lifetime of the intermediate state. The achievement of two-photon interference with photon-pair sources generated from inhomogeneous atomic ensembles constitutes an important result for time-energy entanglement based on an atom-photon interaction.
A scheme for the generation of nonclassical pairs of photons in atomic vapors is proposed. The scheme exploits the fact that the cross correlation of the emission of photons from the extreme transitions of a four-level cascade system shows antibunching, unlike the case of the three-level cascade emission, which shows bunching. The Cauchy-Schwarz inequality, which is the ratio of the cross-correlation to the autocorrelation function, in this case is estimated to be 103−−106{10}^{3}--{10}^{6}103−−106 for controllable time delay, and is one to four orders of magnitude larger compared to previous experiments. The choice of Doppler-free geometry, in addition to the fact that at three-photon resonance the excitation and deexcitation processes occur in a very narrow frequency band, ensures cleaner signals.