Long-lived quantum coherences in symmetric V-system strongly driven by incoherent light

The three-level V-system is a prototype model of quantum coherent dynamics in multilevel systems, including photosynthetic light-harvesting complexes and photovoltaic devices. The symmetric V-system weakly irradiated by incoherent light undergoes coherent dynamics under certain conditions [1]. Here, we explore the coherent dynamics in the limit where incoherent driving is fast compared to the radiative decay rates. The two-photon quantum coherences between the excited levels of the symmetric V-system display an oscillatory behavior in the underdamped regime ($\Delta/\gamma > \bar{n}$) and reach a long-lived quasi-stationary state in the overdamped regime ($\Delta/\gamma < \bar{n}$) for the effective photon occupation numbers $\bar{n}\gg 1$. The lifetime of the long-lived coherent state scales as $\bar{n}(\Delta/\gamma)^{-2}$ for $p>p_c$, where $p_c$ is a critical value of the transition dipole alignment factor ($p_c= 1-\varepsilon$ with $\varepsilon \to 0$ over a wide range of excited-level splittings $\Delta$ and radiative decay rates $\gamma$). For $p