Open quantum random walks: bi-stability on pure states and ballistically induced diffusion

Abstract: Open quantum random walks (OQRWs) deal with quantum random motions on the line for systems with internal and orbital degrees of freedom. The internal system behaves as a quantum random gyroscope coding for the direction of the orbital moves. We reveal the existence of a transition, depending on OQRW moduli, in the internal system behaviors from simple oscillations to random flips between two unstable pure states. This induces a transition in the orbital motions from usual diffusion to ballistically induced diffusion with large mean free path and large effective diffusion constant at large time. We also show that mixed states of the internal system are converted into random pure states during the process. We touch upon possible experimental realizations.