Preparation of the four-qubit cluster states in cavity QED and the trapped-ion system

This paper proposes a simple scheme to generate afour-atom entangled cluster state in cavity quantum electrodynamics.With the assistantce of a strong classical field the cavity is onlyvirtually excited and no quantum information will be transferredfrom the atoms to the cavity during the preparation for a four-atomentangled cluster state, and thus the scheme is insensitive to thecavity field states and cavity decay. Assuming that deviation oflaser intensity is 0.01 and that of simultaneity for the interactionis 0.01, it shows that the fidelity of the resulting four-atomentangled cluster state is about 0.9886. The scheme can also beused to generate a four-ion entangled cluster state in a hottrapped-ion system. Assuming that deviation of laser intensity is0.01, it shows that the fidelity of the resulting four-ion entangledcluster state is about 0.9990. Experimental feasibility forachieving this scheme is also discussed.