Quantum coherence of Gaussian states in curved spacetime

We study quantum coherence of two-mode Gaussian states in the background of an asymptotically flat black hole. We find that quantum coherence between mode A observed by an inertial observer Alice and mode B observed by an accelerated Bob who hovers near the event horizon is reduced by the Hawking thermal bath. However, it does not vanish in the limit of infinite Hawking temperature but is frozen to a certain value that is an increasing function of the squeezing parameter. We also find that the quantum coherence between Alice and Anti-Bob, Bob and Anti-Bob, increases with the Hawking temperature, which implies the transfer and/or generation of the quantum coherence assisted by the Hawking effect. Finally the additivity relationship of quantum coherence is discussed and a stronger monogamy for the considered system is discovered.