Quantum coherence for an atom interacting with an electromagnetic field in the background of cosmic string spacetime

We investigate the behaviors of quantum coherence (QC) for an atom coupled to the fluctuating electromagnetic field under the cosmic string spacetime. It is found that vacuum fluctuation, atomic polarization and nontrivial spacetime topology affect the QC behaviors. When deficit angle parameter nu =1 and atom is far away from the string, the results restore to that of free Minkowski spacetime. When atom lies in the string and is transversely polarizable, the atom seems like a closed system, and QC completely is not affected by the electromagnetic fluctuation. For nonzero atom-string distance, QC presents oscillatory behaviors as atom-string distance changes, and larger deficit angle parameter causes more prominent oscillation. In a sense, the string can protect the QC to some extent, which is similar to the boundary effect in Minkowski spacetime. Besides, this atom eventually evolves to an incoherent state, which does not appear to be related to the initial state and other various parameters; this means QC cannot keep for long evolution time in the cosmic string spacetime. In principle, atomic polarization, atom-string distance and deficit angle parameter provide us more freedom to steer the QC behaviors, which might be useful to sense various cosmic string spacetime and distinguish the cosmic string spacetime from Minkowski spacetime.