Incoherent Excitation of Thermally Equilibrated Open Quantum Systems

TL;DR

This paper analytically investigates how incoherent external perturbations affect the dynamics of thermally equilibrated open quantum systems, revealing that such systems exhibit mostly incoherent behavior after initial response, relevant to biological light-harvesting processes.

Contribution

It provides a non-Markovian analytical model to study incoherent excitation effects on open quantum systems, highlighting the limited role of stationary coherences in response to incoherent perturbations.

Findings

Dynamics are incoherent beyond initial response.

Stationary coherences have limited impact on system response.

Results are relevant to light-harvesting molecules in photosynthesis.

Abstract

Under natural conditions, excitation of biological molecules, which display non-unitary open system dynamics, occurs via incoherent processes such as temperature changes or irradiation by sunlight/moonlight. The dynamics of such processes is explored analytically in a non-Markovian generic model. Specifically, a system S in equilibrium with a thermal bath TB is subjected to an external incoherent perturbation BB (such as sunlight) or another thermal bath TB', which induces time evolution in (S+TB). Particular focus is on (i) the extent to which the resultant dynamics is coherent, and (ii) the role of "stationary coherences", established in the (S+TB) equilibration, in the response to the second incoherent perturbation. Results for systems with parameters analogous to those in light harvesting molecules in photosynthesis show that the resultant dynamical behaviour is incoherent beyond a very short response to the turn-on of the perturbation.