  We investigate theoretically the optical properties of an atomic gas which
has been cooled by the laser cooling method velocity-selective coherent
population trapping. We demonstrate that the application of a weak laser pulse
gives rise to a backscattered pulse, which is a direct signal for the
entanglement in the atomic system, and which leads to single-particle
entanglement on the few-photon level. If the pulse is applied together with the
pump lasers, it also displays the phenomenon of electromagnetically induced
transparency. We suggest that the effect should be observable in a gas of
Rubidium atoms.
