Abstract
Noise-assisted transport in quantum systems occurs when quantum time evolution and decoherence conspire to produce a transport efficiency that is higher than what would be seen in either the purely quantum or purely classical cases. In disordered systems, it has been understood as the suppression of coherent quantum localization through noise, which brings detuned quantum levels into resonance and thus facilitates transport. We report several new mechanisms of environment-assisted transport in ordered systems, in which there is no localization to overcome and where one would naively expect that coherent transport is the fastest possible. Although we are particularly motivated by the need to understand excitonic energy transfer in photosynthetic light-harvesting complexes, our model is general—transport in a tight-binding system with dephasing, a source and a trap—and can be expected to have wider application.
Highlights
Trapped as opposed to lost, regardless of how fast the transport is
We do not average over initial sites, which allows us to explain the absence of environment-assisted quantum transport (ENAQT) in end-to-end transport
We can see that ENAQT is possible in all configurations except when the initial site is located opposite the trap
Summary
There is no general solution, ENAQT can be determined analytically in every particular finite system, which is how Plenio and Huelga proved that ξ = 0 in the case with the origin and trap at opposite ends of the chain [5]. The solution is by Gaussian elimination (see the appendix), meaning that η is a rational function of γ , κ and μ. ENAQT is calculated by maximizing this function with respect to γ. Κ2(20μ4 + 7μ2 + 9)μ + 32κμ6 + 16κμ4 + 7κμ2 − κ + 16μ7 + 8μ5 − 4μ3 − 2μ 0, meaning that there is a region in the (μ, κ) plane in which ENAQT is impossible, as shown in figure 2. In all other cases, obtained as ENAQT κ and μ siismsutrltiacntleyopuoslsyititveen.dTtohezemroaxwimhiulme kEeeNpAinQgTμis=ξκm/ax2=√37.−In4t√ha3t
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