Quantum coherence in a photosynthetic dimer driven by incoherent sunlight*

In this work, we demonstrate noise-induced coherence in a model of a photosynthetic molecular dimer driven by an incoherent radiation field. Through perturbation theory associated with white noise approximation, the dynamics of the excitons is characterized by the dressed exciton states. The exciton coherence exhibits respectively quantum beats among the exciton states and quasistationary relaxation processes in two opposite parameter limits. We further examine the steady-state physics, where the exciton coherence can be classified into light-induced and trap-induced coherences that break detailed balance. At last, the steady-state population and energy fluxes in the dimer system are discussed.