Non-classical photon pair generation in atomic vapours

TL;DR

This paper proposes a new scheme for generating non-classical photon pairs in atomic vapours, demonstrating anti-bunching and a significant violation of classical correlation bounds with cleaner signals.

Contribution

It introduces a novel four-level cascade scheme that exhibits anti-bunching and large Cauchy-Schwarz inequality violations, unlike previous three-level systems.

Findings

Cross correlation shows anti-bunching, unlike three-level systems.

Cauchy-Schwarz ratio estimated between 10^3 and 10^6.

Doppler-free geometry yields cleaner signals.

Abstract

A scheme for the generation of non-classical pairs of photons in atomic vapours 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 anti-bunching which has not been reported earlier and which is unlike the case of the three level cascade emission which shows bunching. The Cauchy-Schwarz inequality which is the ratio of cross-correlation to the auto correlation function in this case is estimated to be $10^3-10^6$ 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/deexcitation processes occur in a very narrow frequency band, ensures cleaner signals.