Bipartite quantum correlations in a fast-light medium generated with four-wave-mixing in rubidium vapour

Abstract

We investigate the propagation of pre-existing quantum correlations through a fast-light medium with an experiment based on two successive four-wave mixing processes in rubidium vapour.The four-wave mixing process allows both the generation of a large negative group index near its gain-line features [1-3] and the generation of strongly correlated twin-beams [4]. Here we create a pair of twin beams with -2.5 dB intensity difference squeezing and send one of the beams through a second four-wave mixing process, which acts as a fast light medium. As indicated in Fig.1, the noise-characteristics of the fast-light system in a small parameter range allow us to investigate the propagation of bipartite correlations through a region of anomalous dispersion with little added noise. This may allow us to characterize the quantum limits of fast-light propagation [5], both for bright twin-beam states and for two-mode squeezed-vacuum states [6]. Fig.