Quantum interferences and the question of thermodynamic equilibrium - art.no. 023818

We derive from first principles the dynamical equations for the interaction between a heat bath and a multilevel atom with some near degenerate states . Such dynamical equations exhibit atomic coherence terms which arise from the interference of transition amplitudes. We address the question whether such equations lead to a steady state that is consistent with the thermodyn amic equilibrium. We show that coherence affects the dynamics of the system , but the equilibrium conditions are still characterized by Boltzmann facto rs. We also show how an asymmetric treatment of spontaneous and stimulated processes could lend to a steady state which is at variance with the princi ples of thermodynamic equilibrium. We show that such a steady state con be realized by pumping with broadband laser fields. Finally, we show that cohe rences in the dynamical equations can be probed via the spectrum of fluores cence.