Quantum diffusion in the strong tunneling regime

We discuss the dynamics of a quantum-mechanical wavepacket in a noisy environment (i.e., time-dependent disorder), modeled using a tight-binding Hamlitonian. It has been found that the fluctuating environment may give rise to diffusive behavior (rather than Anderson localization, which occurs for time-independent disorder). We develop a new approach to this problem by considering the dynamics as arising from multiple Landau-Zener crossing events. We find the conditions for the validity of the approach, and use it to calculate how the diffusion constant depends on the noise. The analytical results are corroborated numerically. The results may be applicable to exciton diffusion in photosynthesis and electronic transport in solid-state physics.