We propose a scheme to implement a two-qubit controlled-phase gate for single
atomic qubits, which works in principle with nearly ideal success probability
and fidelity. Our scheme is based on the cavity input-output process and the
single photon polarization measurement. We show that, even with the practical
imperfections such as atomic spontaneous emission, weak atom-cavity coupling,
violation of the Lamb-Dicke condition, cavity photon loss, and detection
inefficiency, the proposed gate is feasible for generation of a cluster state
in that it meets the scalability criterion and it operates in a conclusive
manner. We demonstrate a simple and efficient process to generate a cluster
state with our high probabilistic entangling gate