Unraveling excitation energy transfer assisted by collective behaviors of vibrations

Abstract

We investigate how collective behaviors of vibrations such as cooperativity and interference can enhance energy transfer in a nontrivial way, focusing on an example of a donor–bridge–acceptor trimeric chromophore system coupled to two vibrational degrees of freedom. Employing parameters selected to provide an overall uphill energy transfer from donor to acceptor, we use numerical calculations of dynamics in a coupled exciton–vibration basis, together with perturbation-based analytics and calculation of vibronic spectra, to identify clear spectral features of single- and multi-phonon vibrationally-assisted energy transfer (VAET) dynamics, where the latter include up to six-phonon contributions. We identify signatures of vibrational cooperation and interference that provide enhancement of energy transfer relative to that obtained from VAET with a single vibrational mode. We observe a phononic analogue of two-photon absorption, as well as a novel heteroexcitation mechanism in which a single phonon gives rise to simultaneous excitation of both the trimeric system and the vibrational degrees of freedom. The impacts of vibrations and of the one- and two-phonon VAET processes on the energy transfer are seen to be quite different in the weak and strong site–vibration coupling regimes. In the weak coupling regime, two-phonon processes dominate, whereas in the strong coupling regime up to six-phonon VAET processes can be induced. The VAET features are seen to be enhanced with increasing temperature and site–vibration coupling strength, and are reduced in the presence of dissipation. We analyze the dependence of these phenomena on the explicit form of the chromophore–vibration couplings, with comparison of VAET spectra for local and non-local couplings.

Noise-Assisted Discord-Like Correlations in Light-Harvesting Photosynthetic Complexes

“…In light of this information, we selected a subsystem that comprises these two important sites, whose energy transfer is mainly controlled by site 2 due to the weak coupling between sites 1 and 3. Interestingly, a similar trimeric chromophore system was used recently to explore the underlying physics of vibrationally-assisted energy transfer [18]. We follow previous authors [6,9,33] that estimate Γ RC = 1 ps −1 .…”

“…One of these is the so-called environment-assisted quantum transport or ENAQT, an effect that arises from the balance between coherent quantum evolution of a photosynthetic system and environmentally induced decoherence [15,16]. More recently, the role of vibrations in efficient transport of photosynthetic energy has been highlighted, giving rise to the so-called vibrationally assisted energy transfer effect [17,18].…”

Interplay of vibration- and environment-assisted energy transfer

“…When the classical noise is present, the energy levels fluctuate. The form of the coupling term σz implies that these two excitations are anticorrelated via the noise source [21,26]. This means that the noise can bring the excitation levels to resonance and thereby enhance the excitation energy transfer efficiency.…”

“…This platform has been used to experimentally study VAET [15], and the addition of classical fluctuations can be easily achieved by noisy modulation of addressing lasers. We have also recently studied the effect of multiple underdamped vibrational modes on energy transfer within the context of a trapped ion simulation [21]. We expect that the predictions made below for regimes of energy transfer can also be validated on the circuit-QED platform [22].…”

Interplay of vibration- and environment-assisted energy transfer

“…This platform has been used to experimentally study VAET [15], and the addition of classical fluctuations can be easily achieved by noisy modulation of addressing lasers. We have also recently studied the effect of multiple underdamped vibrational modes on energy transfer within the context of a trapped ion simulation [22]. We expect that the predictions made below for regimes of energy transfer can also be validated on the circuit-QED platform [23].…”