Optical pumping method for squeezing and entanglement in the ground-state spin subsystems of macroscopic atomic ensembles

Abstract

We describe the mechanism of squeezing and entanglement in the ground-state spin subsystems of macroscopic atomic ensembles via the process of stimulated cooperative Raman-type scattering of correlated photon pairs. This mechanism is analogous to common optical pumping techniques normally used for depopulation of Zeeman sublevels in macroscopic atomic ensembles. We show that, by the excitation of atoms, oriented in their angular momenta, with nonclassical light consisting of a rare flux of strongly correlated photon pairs, essential correlations in the macroscopic spin fluctuations can be transferred and accumulated. In turn this leads to squeezing or entanglement in the quasispin (alignment) subsystems of macroscopic ensembles. We discuss in particular a scheme for an interferometer that would be available for the control or teleportation of quantum states created in quasispin subsystems. Such squeezed and entangled states can be stored in long-lived spin subsystems and can be further used in quantum information protocols based on the continuous variable technique.