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Coherent versus incoherent energy transport: Effects of harmonic deformations

Naghi Behzadi, Bahram Ahansaz

Published Jan 4, 2016• 0 citations
OpenAlex

Abstract

In this work, we study the effects of coherent and incoherent transport of energy through two types of configurations of four interacting two-level systems. Both of the configurations are irreversibly attached to the respective reaction centers. For the first type, the dynamics is only coherent, while for the second one the coherent evolution is completely suppressed and the evolution of the system is only incoherent induced from interaction of the system with fluctuating environments. We calculate the efficiency of transport for both of the configurations in the presence of harmonic deformations. It is found that for a special type of deformations, the efficiency of incoherent transport becomes better than the coherent one.

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In this work, we study the effects of coherent and incoherent transport of energy through two types of configurations of four interacting two-level systems. Both of the configurations are irreversibly attached to the respective reaction centers. For the first type, the dynamics is only coherent, while for the second one the coherent evolution is completely suppressed and the evolution of the system is only incoherent induced from interaction of the system with fluctuating environments. We calculate the efficiency of transport for both of the configurations in the presence of harmonic deformations. It is found that for a special type of deformations, the efficiency of incoherent transport becomes better than the coherent one.
Selective energy transport throughout a quantum network connected to more than one reaction center can play an important role in many natural and technological considerations in photosystems. In this work, we propose a method in which an excitation can be transported from the original site of the network to one of the reaction centers arbitrarily using independent sources of dephasing noises. We demonstrate that in the absence of dephasing noises, the coherent evolution of the system does not have any role in energy transport in the network. Therefore, incoherent evolution via application of dephasing noises throughout a selected path of the network leads to complete transferring of the excitation to a desired reaction center.
We consider the problem of energy transport in a chain of coupled quantum systems with the goal of shedding light on how nonclassical resources can affect transport. We study the cases for which either coherent or incoherent energy hopping takes place in the chain. Here, incoherent energy hopping is referred to as the ``classical'' scenario in allusion to its fully diagonal dynamics in the basis formed by the eigenstates of the decoupled sites. We focus on the case of a linear chain of two-level sites and find a hopping rate threshold above which the coherent quantum case is more efficient than the incoherent counterpart. We then link the quantum hopping rate to the coherence global maximum, which allows us to state that there is a coherence threshold above which the quantum scenario is more efficient. Next, we consider the integrated coherence generated by the dynamics and show how it is related to what is known as the invasiveness of a quantum operation. Our results strongly suggest the significant role played by quantum invasiveness as a resource for quantum transport.
Coherent control of energy transport in a non-equilibrium steady-state (NESS) in a reaction-center-connected donor-acceptor pair is proposed. The pigments are considered to be continuously interacting with incoherent radiation and a phonon bath while being driven by phase-controlled coherent fields. Coherent excitation of the donor-acceptor pair is shown to induce interference between excitation pathways, resulting in phase dependent modulation of the flux. As a consequence one can enhance or suppress energy transfer via interference, e.g. an optical energy switch. The persistence of such interference enables coherent control at a NESS in dissipative regime suggests an extension of the operational scope of quantum control from traditional transient domain with low dissiaption to noisy environment NESS at room temperature.
We investigate coherent and incoherent excitation transfer in a random network with dipole–dipole interactions as a model system describing energy transport, e.g., in photosynthetic light-harvesting complexes or gases of cold Rydberg atoms. For this purpose, we introduce and compare two different measures (the maximum output probability and the average transfer time) for the efficiency of transport from the input to the output site. We especially focus on optimal configurations which maximize the transfer efficiency and the impact of dephasing noise on the transport dynamics. For most configurations of the random network, the transfer efficiency increases when adding noise, giving rise to essentially classical transport. These noise-assisted configurations are, however, systematically less efficient than the optimal configurations. The latter reach their highest efficiency for purely coherent dynamics, i.e. in the absence of noise. 1.
The investigation of the phenomenon of dephasing assisted quantum transport, which happens when the presence of dephasing benefits the efficiency of this process, has been mainly focused on Markovian scenarios associated with constant and positive dephasing rates in their respective Lindblad master equations. What happens if we consider a more general framework, where time-dependent dephasing rates are allowed, thereby, permitting the possibility of non-Markovian scenarios? Does dephasing-assisted transport still manifest for non-Markovian dephasing? Here, we address these open questions in a setup of coupled two-level systems. Our results show that the manifestation of non-Markovian dephasing-assisted transport depends on the way in which the incoherent energy sources are locally coupled to the chain. This is illustrated with two different configurations, namely non-symmetric and symmetric. Specifically, we verify that non-Markovian dephasing-assisted transport manifested only in the non-symmetric configuration. This allows us to draw a parallel with the conditions in which time-independent Markovian dephasing-assisted transport manifests. Finally, we find similar results by considering a controllable and experimentally implementable system, which highlights the significance of our findings for quantum technologies.