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Optics and Spectroscopy

Entangled states in spin subsystems of polyatomic ensembles

Dmitriy V. Kupriyanov, Igor M. Sokolov, A. V. Slavgorodskii

Published May 1, 2003• 0 citations
Publisher

Abstract

The feasibility of formation entangled states in spin subsystems of two spatially separated atomic ensembles is discussed. It is shown that the process of cooperative Raman scattering of correlated photon pairs emitted by a parametric source in a below-threshold regime may serve as a physical mechanism for the entanglement. A scheme of teleportation of a coherent spin state in systems of spatially separated ensembles is proposed.

DOI
10.1134/1.1576841

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Jun 10, 2013•1 citation
The feasibility of formation entangled states in spin subsystems of two spatially separated atomic ensembles is discussed. It is shown that the process of cooperative Raman scattering of correlated photon pairs emitted by a parametric source in a below-threshold regime may serve as a physical mechanism for the entanglement. A scheme of teleportation of a coherent spin state in systems of spatially separated ensembles is proposed.
In this paper we consider the optical coupling of two four-level 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 Einstein-Podolsky-Rosen system in different applications pursuing the goal of spreading quantum information schemes in atomic subsystems.
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.
Spontaneous Raman scattering (SRS) in atomic ensembles provides a promising method to generate spin-wave--photon entangled states. In the past experiments, a spin-wave--photon entangled state was produced via SRS from an atomic ensemble. Here, we report a scheme of simultaneously generating two spin-wave--photon (atom-photon) entangled states in a cold Rb ensemble via SRS. Based on joint Bell-state measurements on the two photons coming from the two atom-photon entangled sources, respectively, we projected the two stored spin waves into a Bell state and then mapped the quantum memory into a polarization-entangled photon pair. Such a polarization-entangled photon pair can be released on demand and thus the presented scheme has potential application in the preparation of large-size photonic entangled states.
A proposal is made for the creation of macroscopic quantum states of collective atomic-ensemble variables by the use of stimulated Raman scattering (SRS), followed by conditional optical measurement. After the completion of the SRS process, one is able to reverse the process and to return all the atoms to their ground states in such a way that reads out an arbitrary quantum state of the collective atomic field and writes this state onto the outgoing optical field. This scheme can be used for the creation of entanglement between two distant atomic ensembles. The quantum analysis of the SRS process treats one-dimensional spatial-temporal propagation accurately. Remarkably, it is found that this multimode problem can be simplified to a two-mode problem involving spatial-temporal wave-packet modes of the optical and atomic collective fields. This improves the understanding of the entanglement created in this system.
The two-photon and scattering resonances between the spontaneous emissions of the two- and single- photon transitions of the three-level inverted radiators in the Ξ, V configurations and the system of two-level radiators D, inverted relatively the dipole forbidden transition are revised. This approach opens the new possibilities in the manipulation of the decay process and generation of the entangled photon pairs. The correlation between the V and Ξ cascade three-level subsystems on the two-photon transitions of dipole forbidden radiators is studied, taking into consideration the cooperative scattering and two photon resonances through the vacuum field. One of them corresponds to the situation when the total energy of emitted photons by three level dipole-active radiator in the cascade configuration enters into the two-photon resonance with the dipole-forbidden transitions of second atom. Another effect corresponds to the scattering situation, when the difference of the excited energies of the two dipole-active transitions of V three level radiator are in the resonance with the dipole-forbidden transitions of the second one. These effects are accompanied with the interferences between single- and two-quantum collective transitions of the inverted radiators from the ensemble. The two particle collective decay rate is defined in the description of the atomic correlation functions.