Quantum-phase dynamics of an atomic/molecular system interacting with a two-mode squeezed vacuum field: coexistence of quantum and thermal features

We investigate the dynamics of a three-state atomic/molecular model system interacting with a two-mode squeezed vacuum field in view of the correlation between the atomic/molecular density matrix and photon-phase distribution. It is found that two-mode squeezed vacuum field realizes the anomalous situation that the coherency between the atomic/ molecular states concerning the two-photon process is preserved well during the dynamics though the coherency between other states completely vanish. This implies that the quantum and thermal features can coexist in the atomic/ molecular system in the presence of two-mode squeezed vacuum field. Such phenomenon is found to originate in the feature of its initial photon-phase correlation of a two-mode squeezed vacuum. We also discuss how the present attractive features in off-diagonal density matrices affect the molecular non-linear polarization. (C) 2002 Elsevier Science B.V. All rights reserved.