  We show that high squeezing and entanglement can be generated at the output
of a cavity containing atoms interacting with two fields in a Coherent
Population Trapping situation, on account of a non-linear Faraday effect
experienced by the fields close to a dark-state resonance in a cavity.
Moreover, the cavity provides a feedback mechanism allowing to reduce the
quantum fluctuations of the ground state spin, resulting in strong steady state
spin-squeezing.
