Enhanced coupling between waveguides through randomness

Amorphous systems possess various non-intuitive features, entirely based on their intrinsic random structure and absence of any long-range order [1]. One of their most striking properties is the existence of a gap in the spectrum of eigenstates despite the lack of Bragg scattering [2]. Recently, the concept of amorphous lattices exhibiting a band gap was introduced in optics, and demonstrated using a liquid-like arrangement of waveguides [3]. In our experiments of [3], we demonstrated an isolated defect state residing deep inside the gap. But how do defect states interact with one another? What is the nature of this interaction? Can defect states interact over great distances? To answer these questions, we present a comprehensive experimental and theoretical study on coupled defect states in an amorphous band-gap lattice, and find an enhancement of coupling arising from the random environment surrounding the defects.