Transient subdiffusion via disordered quantum walks

Transport phenomena play a crucial role in modern physics and applied sciences. Examples include the dissipation of energy across a large system, the distribution of quantum information in optical networks, and the timely modeling of spreading diseases. In this work we experimentally prove the feasibility of disordered quantum walks to realize a quantum simulator that is able to model general transient subdiffusive phenomena, exhibiting a sublinear spreading in space over time. Our experiment simulates such phenomena by means of a finely controlled insertion of various levels of disorder during the evolution of the walker, enabled by the unique flexibility of our setup. This allows us to explore the full range of subdiffusive behaviors, ranging from anomalous Anderson-like localization to normal diffusion for all experimentally accessible step numbers.