Effect of Pulse Shaping on Observing Coherent Energy Transfer in Single Light-Harvesting Complexes

Abstract

Recent experimental and theoretical studies have revealed that quantum coherence plays an important role in the excitation energy transfer in photosynthetic light-harvesting (LH) complexes. Inspired by the recent single-molecule two-color double-pump experiment, we theoretically investigate the effect of pulse shaping on observing coherent energy transfer in the single bacterial LH2 complex. It is found that quantum coherent energy transfer can be observed when the time delay and phase difference between the two laser pulses are controlled independently. However, when the two-color pulses are generated using the pulse-shaping method, how the laser pulses are prepared is crucial to the observation of quantum coherent energy transfer in single photosynthetic complexes.

Analysis of Photosynthetic Systems and Their Applications with Mathematical and Computational Models

“…These studies are also supporting the existence of quantum coherence which is a subject of continuing debate [69][70][71][72][73][74][75][76]. The study of pump-probe polarization phenomena of the photosynthetic light harvesting complexes has also been reported in the previous works for several kinds of coherences and the long-time vibronic coherences have been observed in the FMO [77][78][79]. The electron-nuclear interaction in the BChl systems of the FMO complex has also been described in a molecular dynamics-based study of [80], which also signifies the influence of electronic relaxation caused by the environmental changes.…”

Theoretical study of excitation energy transfer and nonlinear spectroscopy of photosynthetic light‐harvesting complexes using the nonperturbative reduced dynamics method

“…Since the HEOM formalism can incorporate external fields directly into the equations of motion, it is also possible to directly simulate the experiments where the EET dynamics driven by a set of laser pulses. One of such study is performed in Reference 102, where Song et al simulated the EET dynamics between the B800 and B850 rings of the LH2 complex in a double pump experiment 103 . The goal is to find out whether control of phases between the 2 two‐color pump laser pulses can lead to significant quantum beats on the EET dynamics, as observed in the single complex experiment in Reference 103.…”

“…In the second scheme where the pulse shaping method only modifies the phase profile, no quantum coherence is observed in the weak excitation regime, since the total laser power spectrum is not altered. 102 In the third scheme, when both the amplitude and phase profiles are modulated in the pulse shaping method, quantum beats can be observed again. F I G U R E 4 Simulated population dynamics of the B800 and B850 manifolds in the LH2 complex, driven by two consecutive independent 30 fs pump pulses.…”

“…Simulated population dynamics of the B800 and B850 manifolds in the LH2 complex, driven by two consecutive independent 30 fs pump pulses 102 . The time delay is Δ t = 102 fs between the pulse centers, and the phase difference is Δ ϕ = 0…”

“…In Reference 102, three different cases of the phase relations between the two pump pulse pairs were studied: (a) The two laser pulses centered around 800 and 850 nm are independent, such that the time delay and phase difference between them can be controlled independently; (b) The two pump laser pulses are generated by pulse shaping from a single laser pulse with a phase slope applied to the lower frequency part of the laser spectra, mimicking the experimental setup in Reference 103; (c) The two‐color pump pulses are generated using pulse shaping methods where both the amplitude and phase profiles are modified. The observable of the simulation is the final population on the B850 complex, which can be measured in the experiments through the fluorescence signal.…”