Light Avoids Anderson Localization

The confinement of waves in a disordered medium—Anderson localization [1]—has been observed for electromagnetic [2, 3] and acoustic [4] waves in disordered dielectric structures, and for electron waves in condensed matter. Anderson localization arises as a result of the constructive interference between waves that follow time reversed paths as they loop back to a point as a result of scattering from defects. The effect is common in low-dimensional disordered systems because the restricted volume explored by scattered waves enhances the likelihood that waves will return to a point. Now, a new experiment conducted by Mohammad Hafezi at the Joint Quantum Institute of NIST and the University of Maryland, College Park, and collaborators reveals the virtually unimpeded flow of photons—the opposite of Anderson localization—in a one-dimensional channel along the edges of a two-dimensional disordered lattice. These findings, reported in Physical Review Letters[5], may inspire new ways of engineering photonics devices such as filters, switches, and delay lines that rely on the controlled propagation of light.