Quantum walk in stochastic environment

We consider a quantized version of the Sinai-Derrida model for "random walk in random environment."The model is defined in terms of a Lindblad master equation. For a ring geometry (a chain with periodic boundary condition) it features a delocalization-transition as the bias in increased beyond a critical value, indicating that the relaxation becomes underdamped. Counterintuitively, the effective disorder is enhanced due to coherent hopping. We analyze in detail this enhancement and its dependence on the model parameters. The nonmonotonic dependence of the Lindbladian spectrum on the rate of the coherent transitions is highlighted.