The relativistic quantum channel of communication through field quanta

Setups in which a system Alice emits field quanta which a system Bob receives are prototypical for wireless communication and have been extensively studied. In the most basic setup, Alice and Bob are modelled as Unruh-DeWitt detectors for scalar quanta and the only noise in their communication is due to quantum fluctuations. For this basic setup we here construct the corresponding information-theoretic quantum channel. We calculate the classical channel capacity as a function of the spacetime separation and we confirm that the classical as well as the quantum channel capacity are strictly zero for spacelike separations. We show that this channel can be used to entangle Alice and Bob instantaneously. Alice and Bob are shown to extract this entanglement from the vacuum through a Casimir-Polder effect.