Effects of Counter‐Rotating Couplings on the Dynamics of a Λ System: Long‐Lived Coherence Oscillations

Abstract

AbstractThe time evolution of the ground‐state population and coherence of a Λ‐type three‐level emitter strongly coupled to a radiation reservoir is studied by using a transformed rotating‐wave approximation (TRWA) and time‐dependent variational approach with the multiple Davydov ansatz. The study aims at illustrating the role of counter‐rotating couplings in the long‐time evolution of the Λ system. The TRWA and variational approach are found to be consistent with each other and predict that there exist long‐lived oscillatory behaviors of ground‐state populations and coherence, which are robust in the presence of strong dissipation and arise from the counter‐rotating‐coupling‐induced virtual photon processes. The oscillation amplitude and frequency depend on the system‐reservoir coupling strength and the frequency difference between the two ground states, which can be qualitatively and quantitatively captured by the TRWA analytical results. Present results offer insights into the impact of the counter‐rotating couplings on the long‐time evolution of the strongly dissipative multilevel system as well as the protocol of generation of coherent oscillations by relaxation in a strong‐coupling regime.