We consider various dissipative atom-cavity systems and show that their collective dynamics can be used to maximize entanglement for intermediate values of the cavity leakage parameter κ. We first consider the interaction of a single two-level atom with one of two coupled microwave cavities and show analytically that the atom-cavity entanglement increases with cavity leakage. We next consider a system of two atoms passing successively through a cavity and derive the expression for the maximum value of κ in terms of the Rabi angle gt, for which the two-atom entanglement can be increased. Finally, numerical investigation of micromaser dynamics also reveals the increase of two-atom entanglement with stronger cavity-environment coupling for experimentally attainable values of the micromaser parameters.

We study the efficiency of two-qubit mixed entangled states as resources for quantum teleportation. We first consider two maximally entangled mixed states, viz., the Werner state\cite{werner}, and a class of states introduced by Munro {\it et al.} \cite{munro}. We show that the Werner state when used as teleportation channel, gives rise to better average teleportation fidelity compared to the latter class of states for any finite value of mixedness. We then introduce a non-maximally entangled mixed state obtained as a convex combination of a two-qubit entangled mixed state and a two-qubit separable mixed state. It is shown that such a teleportation channel can outperform another non-maximally entangled channel, viz., the Werner derivative for a certain range of mixedness. Further, there exists a range of parameter values where the former state satisfies a Bell-CHSH type inequality and still performs better as a teleportation channel compared to the Werner derivative even though the latter violates the inequality.

We study the entanglement properties of a pair of two-level atoms going through a cavity one after another. The initial joint state of two successive atoms that enter the cavity is unentangled. Interactions mediated by the cavity photon field result in the final two-atom state being of a mixed entangled type. We consider the field statistics of the Fock state field, and the thermal field, respectively, inside the cavity. The entanglement of formation of the joint two-atom state is calculated for both these cases as a function of the Rabi angle gt. We present a comparitive study of two-atom entanglement for low and high mean photon number cases corresponding to the different fields statistics.

We consider a realistic model for the one-atom micromaser consisting of a cavity maintained in a steady state by the streaming of two-level Rydberg atoms passing one at a time through it. We show that it is possible to monitor the robust entanglement generated between two successive experimental atoms passing through the cavity by the control decoherence parameters. We calculate the entanglement of formation of the joint two-atom state as a function of the micromaser pump parameter. We find that this is in direct correspondence with the difference of the Shannon entropy of the cavity photons before and after the passage of the atoms for a reasonable range of dissipation parameters. It is thus possible to demonstrate information transfer between the cavity and the atoms through this set-up. The generation of quantum entanglement in atomic systems is being vigorously pursued in recent years. The primary motivation for this upsurge of interest is to test the applicability of the ongoing conceptual developments in quantum information theory and through them the implementation of current quantum communication and computation protocols [1]. Several schemes have been proposed recently to engineer the entanglement of two [2] or more atoms [3,4]. Many of these proposals are for generating entanglement in a probabilistic manner. Since a large number of these proposals rely on the trapping or slow passage of cold atoms through optical cavities [5], the efficient control of cavity leakage and atomic dissipation is a major concern [6]. The value of the atom-cavity coupling g is very close to the values of photonic and atomic decay rates κ and Γ, respectively, in the parameter ranges operated by optical cavities. Thus decoherence effects are significant even in the time O(1/g) needed for perceptible entanglement.The micromaser, described below, is appreciated as a practical device for processing quantum information. The formation of atom-photon entanglement and the subsequent generation of correlations between spatially separated atoms has been shown using the micromaser. The nonlocal correlations developed in this fashion between two or more atoms can be used to test the violation of Bell-type inequalities [7,8,9,10]. Since for Rydberg atoms tuned with microwave frequencies, κ ≪ g, and Γ is negligible, decoherence does not crucially affect the individual single atom dynamics. However, dissipation does build up over the passage of a number of atoms through the micromaser, and is revealed in the photonic statistics of the steady-state cavity field, as was discussed in Ref. [8]. The entanglement between a pair of atoms pumped at the same time through a micromaser has been analysed in Ref. [9]. It is rather difficult to practically realize such a set-up though. The genuine one-atom micromaser, on the other hand, can be operated over a reasonably large region of parameter space, and is thus a feasible device [11] for generating entanglement between two or more atoms. Recently, Englert et al [10] have shown using a non-separabilit...

We constructed a class of non-maximally entangled mixed states [1] and extensively studied its entanglement properties and also their usefulness as teleportation channels. In this article, we revisited our constructed state and have studied it from three different perspectives. Since every entangled state is associated with an witness operator, we have found a suitable entanglement as well as teleportation witness for our non-maximally entangled mixed states. We considered the noisy channel's effects on our constructed state and to see whether it affects the states' capacity as teleportation channel. For this purpose we have mainly emphasized on amplitude damping channel. A comparative study with concurrence and quantum discord of the state of ref.[1] has also been carried out here.