Applications of correlated photon pairs : sub-shot noise interferometry and entanglement

Abstract

Using cesium atoms weakly coupled to a low-finesse cavity, we have generated photon pairs that are highly correlated in a non-classical way, as demonstrated by a large violation of the Cauchy-Schwartz inequality G = 760 +2100 -320 for a bin width T = 60 ns. Biphoton interferometry of the correlated pairs via the Holland-Burnett scheme holds promise to demonstrate precision beyond the shot noise limit, although the current interference fringe visibility of [beta]= 0.84 ± 0.04 only translates to a shot noise limited phase uncertainty. Polarization-time entangled pairs can also be directly generated, by optically pumping the atoms to both F = 3, mF = ±3 ground states. The degree of entanglement, expressed by the calculated fidelity f = 0.81 ± 0.09 and calculated Bell state parameter S = 2.3 ± 0.2, is estimated to be finite but not maximal.