Linear-Optical Proposal for Implementation of the Two-Logic-Qubit Controlled Phase Gate in Decoherence-Free Subspace with Conventional Photon Detectors

Abstract

A linear-optical scheme is proposed to implement the nondeterministic two-qubit controlled phase gate in decoherence-free subspace (DFS) with a certain success probability. The proposed setup requires simple linear-optical elements, two pairs of the two-photon polarization entangled states as auxiliary resource, and the conventional photon detectors that only distinguish the vacuum and nonvacuum Fock number states. A sophisticated single-photon detector distinguishing one or two photon states is unnecessary. This makes the protocol more realizable in experiments.