  We study the entanglement in a system consisting of two non-interacting atoms
located in separate cavities, both in their ground states. A single incoming
photon has a non-zero probability of entering either of the two cavities. The
Jaynes-Cummings interaction in the rotating wave approximation describes the
coupling of each atom with the radiation field. We compute and analyze the
atom-atom entanglement, the entanglement between the two photon modes, and also
the entanglement between each atom and each photon mode. The measure of
entanglement is the von Neumann entropy. For the case in which the two
atom-photon systems have identical properties, but allowing for non-resonant
conditions, the sum of the atom-atom and photon-modes-entanglement is time
independent. The effect of detuning is to decrease the strength of the largest
entanglement achieved and to shorten the time for it to occur. The results
support the fact that the state of the photons after emergence from cavities is
entangled, notwithstanding its single-particle nature. In addition, for the
case of resonance and identical cavity parameters, we demonstrate that von
Neumann entropy is always greater than or equal to the measure of entanglement
known as negativity.
