Maximal atom-photon entanglement in an N-type atomic system

Atom-photon entanglement provides an essential resource for quantum communication and quantum computation. How to conveniently and efficiently achieve a maximal entanglement between atomic system and spontaneous emission field has been a challenging task. Here, we present a simple, yet we believe a powerful, method to generate entangled states between photons and an N-type atomic system. Beside the achievement of a nearly perfect entanglement, we also examine evidence for a link between entanglement and populations in dressed and bare states; It is found that a maximal entanglement can be established when populations in both dressed and bare states are spread over states. Moreover, the system would be disentangled in the absence of evenly distributed populations, another reason for further strengthen our claim that the physical origin of such entanglement is quantum correlation produced by distribution of the populations. We then discuss the dependence of the entanglement on Rabi frequency and detuning of the applied fields and demonstrate how an almost complete entanglement can be achieved for a judicious choice of these parameters. Note that entanglement is measured in semi-classical regime and by solving density matrix equations of motion and von-Neumann entropy.