Quantum Correlation without Entanglement in a Two-Atom-Vacuum Field System

Quantum correlation without entanglement in a two-atom-vacuum field system is investigated. The influence of the atomic dipole-dipole interaction on quantum correlation is also examined. We find that, when both atoms are initially in separable excited states, the quantum discord of two atoms appears while their entanglement wholly vanishes throughout the evolution. We explain our results in detail. Our results provide a novel method of achieving a quantum correlation resource without entanglement in the real system.