Figure 1: Environment-assisted quantum transport (ENAQT).

(a) Photosynthetic antenna complexes are networks of chlorophylls that collect and transfer solar energy. A well-studied example is the Fenna–Matthews–Olson complex of green sulphur bacteria, here depicted as a network of seven sites that transports excitation energy from initial site 1 to target site 3 (adapted with permission from ref. 49). Simulations have suggested that this transport may be enhanced by decoherence^5,6,7. (b) We simulate an instance of ENAQT on a lattice of four sites, with site 1 initially excited and site 3 the target. If the detuning Δβ of site 4 equals C, one of the system eigenmodes has no occupancy at site 3 and cannot couple to the sink; by broadening the levels, decoherence breaks the condition Δβ=C, allowing all eigenmodes to couple to the sink and thus increasing transport efficiency. (c) Our simulator consists of four coupled waveguides arranged as shown (cross-section). The sink is modelled with a large array of closely coupled waveguides that transport light away from the main four waveguides. At the central wavelength λ₀, waveguide 4 has propagation constant β+Δβ, while the others have propagation constant β. (d) Theoretical expectation of transport enhancement for this system, as a function of simulation length z and decoherence strength γ. The red bar indicates the region explored experimentally.