Cooperative Ramantype transitions in a system of two fourlevel atoms: Entanglement in the spin subsystem of two spatially separated atomic ensembles
Abstract
In this paper we consider the optical coupling of two fourlevel atoms via cooperative Raman scattering of correlated photons of the nondegenerate spontaneous parametric radiation. The Raman scattering of twin photons incident on the atoms is additionally stimulated by coherent classical radiation in such a way that it is slightly off resonant for each atom considered independently but resonant for the joint system. We discuss the special excitation conditions when the amplitude of the cooperative stimulated Raman scattering from quantum to classical modes becomes greater than the normal transition rates associated with independent Raman scattering. In certain conditions weak entanglement between the Zeeman sublevels in the ground states of these atoms can appear. The small admixture of entanglement in the system of two atoms leads to strong entanglement between transverse macroscopic spin fluctuations of two spatially separated atomic ensembles coupled by such quantum light. The proposed mechanism of entanglement is relevant to the ground state spin subsystem of two distant macroscopic and optically thin atomic ensembles. Such an entangled state can be stored for a long time and used as a basic EinsteinPodolskyRosen system in different applications pursuing the goal of spreading quantum information schemes in atomic subsystems.
 Publication:

Physical Review A
 Pub Date:
 June 2001
 DOI:
 10.1103/PhysRevA.63.063811
 Bibcode:
 2001PhRvA..63f3811K
 Keywords:

 42.50.Ct;
 42.50.Lc;
 42.50.Fx;
 Quantum description of interaction of light and matter;
 related experiments;
 Quantum fluctuations quantum noise and quantum jumps;
 Cooperative phenomena in quantum optical systems