Long-lived quantum coherent dynamics of a \(\Lambda\)-system driven by a thermal environment

We present a theoretical study of quantum coherent dynamics of a three-level \(\Lambda\) system driven by a thermal environment (such as blackbody radiation), which serves as an essential building block of photosynthetic light-harvesting models and quantum heat engines. By solving the nonsecular Bloch-Redfield master equations, we obtain analytical results for the ground-state population and coherence dynamics and classify the dynamical regimes of the incoherently driven \(\Lambda\)-system as underdamped and overdamped depending on whether the ratio \(\Delta/[r f(p)]\) is greater or less than one, where \(\Delta\) is the ground-state energy splitting, \(r\) is the incoherent pumping rate, and \(f(p)\) is a function of the transition dipole alignment parameter \(p\). In the underdamped regime, we observe long-lived coherent dynamics that lasts for \(\tau_c\simeq 1/r\), even though the initial state of the \(\Lambda\)-system contains no coherences in the energy basis. In the overdamped regime for \(p = 1\), we observe the emergence of coherent quasi-steady states with the lifetime \(\tau_{c} = 1.34 (r/\Delta^{2})\), which have low von Neumann entropy compared to the conventional thermal states. We propose an experimental scenario for observing noise-induced coherent dynamics in metastable He\(^*\) atoms driven by x-polarized incoherent light. Our results suggest that thermal excitations can generate experimentally observable long-lived quantum coherent dynamics in the ground-state subspace of atomic and molecular \(\Lambda\) systems in the absence of coherent driving.