Robust entanglement in atomic systems

Abstract

Various models for generation of robust atomic entangled states and their implementation with current accessible technologies are proposed and worked out. Deterministic creation of long living Bell states with respect to metastable states in three-level Λ type systems is studied. Strong atom-field coupling drives atoms into a transient entangled state followed by an irreversible evolution towards a long-living maximally entangled state featuring robustness against dipole-allowed transitions. First, generation of pairwise atomic entanglement in cavities in ideal case is discussed, extension to multi-party entangled states is made. Observation of photons emitted from the system signals the generation of a Bell state. The interaction of multi-level atoms with body-assisted electro-magnetic field in the presence of dispersing and absorbing media is studied and these results are applied to the description of a pair of Λ type atoms passing by a microsphere. Microspheres give rise to resonances of well defined height and width with easy access to strong and weak coupling regimes for atom-field interaction, thus enabling realization of the proposed scheme of ”robust entanglement of three-level atoms”. Even in realistic settings it is possible to obtain quite high amount of entanglement at spatially well separated distances. Then we focus on steady state entanglement between atomic dipoles. It is shown that two dipoles in free space driven by a classical driving field become entangled in the steady state. The crucial point is that, this entanglement is irrespective of the initial state and may be preserved as long as the engineered system is kept intact. Absorption effects in real cavities are studied, and an input-output relation is formulated in the presence of a source in the cavity. Extraction of non-classical photon states from a cavity is investigated.