Engineering Entanglement in Cavity Quantum Electrodynamical Systems

Abstract

Phenomenon of entanglement was justly referred by Erwin Schrödinger as the characteristic trait of the quantum theory. On one hand, the phenomenon helped a lot to clarify the conceptual foundations of the theory. On the other hand, the very same nonlocal, counterintuitive correlations that bind entangled entities are now being employed as a backbone resource for most of the quantum informatics tasks including cryptography, teleportation, entanglement swapping, quantum computation and many others. Therefore controlled engineering of entangled states becomes vitally important. Present work deals with four theoretical proposals for the cavity QED based generation of a variety of entangled atomic and cavity field states including Bell, W, NOON, cluster and graph states. In first two proposals, atom interferometry in Bragg regime has been utilized for the engineering of Bell, W and NOON cavity field states. In this respect, basic constituents of Mach-Zehnder-Bragg (MZB) interferometers i.e. atomic de Broglie wave mirrors and beam splitters have been explored in detail. It is further demonstrated that by manipulating split atomic de Broglie wavepackets in a MZB interferometer, the required states can be engineered in an experimentally feasible manner while utilizing time-tested standard cavity QED tools. This work therefore opens up a new vista for quantum state engineering based on atom interferometry. Remaining two proposals aim at the generation of atomic and cavity field cluster and graph states and employ dispersive as well as resonant atom-field interactions as architectural components of the phase gate. First scheme in this section utilizes the concept of collective eraser whereas the second proposal, the most resource economical one, is based on the simultaneous resonant and dispersive interactions of two two-level atoms with an initially vacuum state high-Q cavity. Here the phase gate operation and hence the state engineering is accomplished when cavity is detected again into vacuum state after culmination of the interactions. Various parameters affecting success probability and fidelity of the proposed protocol have also been elucidated briefly. The parametric dependence of success probability and fidelity on most crucial factors of imprecision in the interaction times have also been plotted for the sake of quantitative assessment. This section is also concluded by providing a comprehensive note on the experimental feasibility of the presented work.