Superradiance Transition in Photosynthetic Light-Harvesting Complexes

Abstract

We investigate the role of long-lasting quantum coherence in the efficiency of energy transport at room temperature in Fenna-Matthews-Olson photosynthetic complexes. The excitation energy transfer due to the coupling of the light harvesting complex to the reaction center ("sink") is analyzed using an effective non-Hermitian Hamiltonian. We show that, as the coupling to the reaction center is varied, maximal efficiency in energy transport is achieved in the vicinity of the superradiance transition, characterized by a segregation of the imaginary parts of the eigenvalues of the effective non-Hermitian Hamiltonian. Our results demonstrate that the presence of the sink (which provides a quasi-continuum in the energy spectrum) is the dominant effect in the energy transfer which takes place even in absence of a thermal bath. This approach allows one to study the effects of finite temperature and the effects of any coupling scheme to the reaction center. Moreover, taking into account a realistic electric dipole interaction, we show that the optimal distance from the reaction center to the Fenna-Matthews-Olson system occurs at the superradiance transition, and we show that this is consistent with available experimental data.

Noise-assisted quantum electron transfer in photosynthetic complexes

“…Inserting ρ 22 (t) into (11) and performing the integration, we find that the ET efficiency is given by…”

“…The primary charge separation occurs on a very short time-scale, of a few picoseconds [1][2][3][4][5]. Because this time-scale is so short, even the room-temperature fluctuations of the protein environment do not destroy the quantum coherent effects, which were recently discovered in these complexes [5][6][7][8][9][10][11][12][13].…”

Superradiance Transition and Nonphotochemical Quenching in Photosynthetic Complexes

“…For those sites which are not connected to sinks, the corresponding ET rates vanish. Under reasonable assumptions, this type of model can be described by an effective non-Hermitian Hamiltonian [2,3,4,5,6].Then, this approach becomes similar to those used in describing the so-called "superradiance transition" (ST) in systems in which the discrete (intrinsic) energy states interact with the continuum spectra [7,8,9,10,11,12]. In these systems, the ST usually occurs when the resonances start to overlap.…”

“…This segregation is called the ST. The ST is a quantum coherent effect and, in biological systems, it should be considered (see, for example, [11,12]) in close relation to the quantum coherent effects studied recently in the photosynthetic complexes [13].It is important to note, that in many systems the occurrence of the ST requires not only the overlapping of the neighboring resonances, but also a delocalization of the eigenfunctions which are involved in the ST. This is especially important for those systems in which the initial wave function does not sufficiently overlap with those eigenfunctions which are responsible for the SR (see below).…”

“…This segregation is called the ST. The ST is a quantum coherent effect and, in biological systems, it should be considered (see, for example, [11,12]) in close relation to the quantum coherent effects studied recently in the photosynthetic complexes [13].…”