  The dynamics of the exciton-photon entanglement, in a semiconductor
microcavity is analyzed. Finding a closed analytical expression for the time
evolution of the concurrence. Using as model two coupled, quantum oscillators
with detuning between them. Supposing that the system is at a temperature
closer to zero. And that the quantum state of the system, remains in the one
excitation sector of the total Hilbert space. The former theoretical setup,
describes the excitons coupled to the photons in the microcavity accurately,
for a system with ultra low density of excitons. We remark in first place, that
our closed expression for the concurrence dynamics. Enable us to establish a
good analytical criterion, to determine the coupling dynamical regime, in which
the system is. Even more, we show that our criterion, is in good agreement with
typically accepted, experimental signatures for strong, and wake coupling
regimes. Finally we present theoretical evidence, suggesting that the
entanglement between the exciton and the photon. Can be measured in
experiments, v\'ia the cross correlation contribution, to the time resolved
spectra of the system.
