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

Abstract

The question of how quantum coherence facilitates energy transfer has been intensively debated in the scientific community. Since natural and artificial lightharvesting units operate under the stationary condition, we address this question via a nonequilibrium steady-state analysis of a molecular dimer irradiated by incoherent sunlight and then generalize the key predictions to arbitrarily complex exciton networks. The central result of the steady-state analysis is the coherence−flux−efficiency relation:where c is the normalization constant. In this relation, the first equality indicates that the energy transfer efficiency, η, is uniquely determined by the trapping flux, which is the product of the flux, F, and branching ratio, κ, for trapping at the reaction centers, and the second equality indicates that the energy transfer flux, F, is equivalent to the quantum coherence measured by the imaginary part of the off-diagonal density matrix, that is,Consequently, maximal steady-state coherence gives rise to optimal efficiency. The coherence−flux−efficiency relation holds rigorously and generally for any exciton network of arbitrary connectivity under the stationary condition and is not limited to incoherent radiation or incoherent pumping. For light-harvesting systems under incoherent light, the nonequilibrium energy transfer flux (i.e., steady-state coherence) is driven by the breakdown of detailed balance and by the quantum interference of light excitations and leads to the optimization of energy transfer efficiency. It should be noted that the steady-state coherence or, equivalently, efficiency is the combined result of light-induced transient coherence, inhomogeneous depletion, and the system−bath correlation and is thus not necessarily correlated with quantum beatings. These findings are generally applicable to quantum networks and have implications for quantum optics and devices.

The origin of loose bound of the thermodynamic uncertainty relation in a dissipative two-level quantum system

“…The expression of mean current (Eq. 8) conforms to the coherence-current relation [50,51] which states that the imaginary part of the coherence (Eq. 7) is responsible for inducing a quantum current between the states.…”

Efficient light harvesting and photon sensing via engineered cooperative effects

“…Finally, under what we call the sunlight configuration (figure 1(d)), we model illumination by natural sunlight, which is isotropic, unpolarized, incoherent and broad-band. This is modeled well as black-body radiation at 6000 K [37,38]. Specifically, in the sunlight configuration the Hamiltonian term H EM is not present, while we include two additional Lindblad dissipators for absorption and stimulated emission induced by sunlight,…”

“…Specifically the coupling between the ring, assumed at thermal equilibrium, and the central core absorber is described with an approach equivalent to the generalized Förster theory, see appendix I. Finally note that in literature three-level models describing exciton transport have been widely used [20,38,[42][43][44]. In particular our approach is similar to the one used in reference [38] where the pumping of sunlight on a dimer system has been considered.…”

Do photosynthetic complexes use quantum coherence to increase their efficiency? Probably not

“…on May 10, 2021 http://advances.sciencemag.org/ Downloaded from (26), but this is an operational definition, which ignores the presence of coherences (off-diagonal terms of the density matrix) (19). Formally, coherence is necessary for observing current because the current is proportional to (the imaginary part of) the off-diagonal elements of the density matrix, e.g., coherences.…”

“…Interest in the dynamics of excitons in the ETC exploded over the past decade, following recent experiments, where ultrafast nonlinear spectroscopy signals showed long-lived oscillations (2)(3)(4)(5)(6)(7)(8). The discovery of coherent oscillations in ETCs pushed forward the hypothesis that in natural photosynthetic complexes, which are extremely efficient, quantum coherence in the presence of an environment is used to assist energy transfer, an idea that has generated much excitement (and debate) (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19).…”