Which-way interference within ringlike unit cells for efficient energy transfer

We show that `which-way' interference within unit-cells enhances the propagation along linear arrays made upon these basic units. As a working example, we address the exciton transfer through linear aggregates of ring-like unit cells, the latter resembling the circular structure of the Light-Harvesting complexes of purple bacteria. After providing an analytic approximate solution of the eigenvalue problem for such aggregates, we show that the population transferred across the array is not a monotonic function of the coupling between nearest-neighbor rings, contrary to what is found from situations where this intra-unit cell interference is not displayed. The non-monotonicity depends on an interesting trade off between the exciton transfer speed and the amount of energy transferred, which is associated with the rupture of symmetry among paths within the ring-like cells, due to the inter-ring coupling strength.