Generation of arbitrary four-atom entangled decoherence-free states

This paper proposes a scheme to generate arbitraryfour-atom entangled decoherence-free states by using simple linearoptical elements, four one-sided cavities in which four atoms areconfined respectively. By conveniently tuning the titled angle ofone half-wave plate, it can obtain arbitrary four-atom entangleddecoherence-free states with a successful probability of 1 as long asthere is no photon loss.