Steady-state Fano coherences in a V-type system driven by polarized incoherent light

Abstract

We explore the properties of steady-state Fano coherences generated in a three-level V-system continuously pumped by polarized incoherent light in the absence of coherent driving. By solving the nonsecular Bloch-Redfield quantum master equation we obtain the ratio of the stationary coherences to excited-state populations, C = (1 + ∆ 2 γ(r+γ) ) −1 , which quantifies the impact of steadystate coherences on excited-state dynamical observables of the V-system. The ratio is maximized when the excited-state splitting ∆ is small compared to either the spontaneous decay rate γ or the incoherent pumping rate r. We demonstrate that while the detrimental effects of a strongly decohering environment generally suppress the coherence-to-population ratio by the factor γ d /γ, an intriguing regime exists where the C ratio displays a maximum as a function of the dephasing rate γ d . We attribute the surprising dephasing-induced enhancement of stationary Fano coherences to the environmental suppression of destructive interference of individual incoherent excitations generated at different times. We further clarify the physical basis for the steady-state Fano coherence, whose imaginary part is identified with the non-equilibrium flux across a pair of qubits coupled to two independent thermal baths, unraveling a direct connection between the seemingly unrelated phenomena of incoherent driving of multilevel quantum systems and non-equilibrium quantum transport in qubit networks. The real part of the steady-state Fano coherence is found to be proportional to the deviation of excited-state populations from their values in thermodynamic equilibrium, making it possible to observe signatures of steady-state Fano coherences in excitedstate populations. Finally, we put forward an experimental proposal for observing steady-state Fano coherences by detecting the total fluorescence signal emitted by Calcium atoms excited by polarized vs. isotropic incoherent light. Our analysis paves the way toward further theoretical and experimental studies of non-equilibrium coherent steady states in thermally driven atomic and molecular systems, and for the exploration of their potential role in biological processes.

Generalized Adiabatic Theorems: Quantum Systems Driven by Modulated Time-Varying Fields

“…This then indicates that the only coherences observed in the slow turn-on limit are those that survive in the steady-state, such as those seen in previous theoretical studies [23,[42][43][44][45].…”

“…Consequently, as illustrated in this example, the open systems adiabatic theorem guarantees that a sufficiently slow turn-on of an incoherent field will only show coherences that survive in the steady-state. In the case of two baths, steady state coherences associated with transport will persist [23,42].…”

Steady-State Analysis of Light-Harvesting Energy Transfer Driven by Incoherent Light: From Dimers to Networks

“…To break the detailed balance and induce steady-state coherence, light-harvesting systems must couple to at least another thermal bath, such as the protein environment or the reaction center, in addition to sunlight radiation. 7,14,17,24 An equilibrium system weakly perturbed by thermal noise assumes the Boltzmann distribution in its eigenstates with zero exciton coherence. Therefore, the nonvanishing steady-state exciton coherence arises from nonequilibrium driving, that is, the excitation by incoherent sunlight and the depletion from the excitation manifold.…”

Steady-State Analysis of Light-harvesting Energy Transfer Driven by Incoherent Light: From Dimers to Networks

“…where we assume that the excitation and trapping occur on difference molecules. Eq (24) holds generally for any exciton networks of arbitrary connectivity under the stationary condition, which is not limited to incoherent radiation or incoherent pumping.…”

“…47,48 In summary, we have demonstrated that steady-state coherence leads to optimal energy transfer in light-harvesting systems. Specifically, as given explicitly in Eq (24), efficiency η is proportional to exciton transfer flux, F , which in turn is determined by quantum coherence…”