Coherent population trapping in the Lambda system by a two-mode quantized field in an SU(2) coherent state

Coherent population trapping (CPT) in a three-level system in the Lambda co nfiguration interacting with two quantized fields is studied. It is shown t hat, in addition to the known trapping states of the field involving ordina ry coherent states of each mode, SU(2) coherent states associated with the Schwinger realization are also field states that give rise to CPT for this system. In addition it is pointed out that superpositions of such states, a nd statistical mixtures of them, for different total photon numbers also gi ve rise to CPT. The stability of the CPT slates against decay of the cavity field modes is examined. CPT is preserved if the modes decay at the same r are. A possible method for generating statistical mixtures of the SU(2) coh erent states is described.