Long-lived quantum coherences in a V-type system strongly driven by a thermal environment

TL;DR

This paper analytically demonstrates that strong thermal pumping can induce long-lived quantum coherences in a three-level V-system, revealing new regimes of sustained quantum coherence influenced by dipole alignment and thermal environment parameters.

Contribution

The study provides exact solutions showing how thermal excitation and dipole alignment affect quantum coherence lifetimes in a V-system, highlighting regimes of long-lived coherence under strong incoherent pumping.

Findings

Long-lived coherences occur in the overdamped regime with strong thermal pumping.

Coherence lifetime scales linearly with photon occupation number for parallel dipoles.

Quasistationary states slow thermalization and depend on dipole alignment.

Abstract

We explore the coherent dynamics of a three-level V-system interacting with a thermal bath in the regime where thermal excitation occurs much faster than spontaneous decay. We present analytic solutions of the Bloch-Redfield quantum master equations, which show that strong incoherent pumping can generate long-lived quantum coherences among the excited states of the V-system in the overdamped regime defined by the condition $\Delta/(\bar{n}\gamma)<f(p)$, where $\Delta$ is the excited-state level splitting, $\gamma$ is the spontaneous decay rate, $\bar{n}\gg 1$ is the effective photon occupation number proportional to the pumping intensity, and $f(p)$ is a universal function of the transition dipole alignment parameter $p$. In the limit of nearly parallel transition dipoles ($p\to 1$) the coherence lifetime $\tau_c = 1.34 (\bar{n}/\gamma) (\Delta/\gamma)^{-2}$ scales linearly with $\bar{n}$ and is enhanced by the factor $0.67 \bar{n}$ with respect to the weak-pumping limit [Phys. Rev. Lett. 113, 113601 (2014); J. Chem. Phys. 144, 244108 (2016)]. We also establish the existence of long-lived quasistationary states, which occur in the overdamped regime and affect the process of thermalization of the V-system with the bath, slowing down the approach to thermal equilibrium. In the case of nonparallel transition dipole moments ($p<1$), no quasistationary states are formed and the coherence lifetime decreases sharply. Our results reveal new regimes of long-lived quantum coherent dynamics, which could be observed in thermally driven atomic and molecular systems.