Convergence of continuous-time quantum walks on the line

The position density of a ``particle'' performing a continuous-time quantum walk on the integer lattice, viewed on length scales inversely proportional to the time $t$, converges (as $t$ tends to infinity) to a probability distribution that depends on the initial state of the particle. This convergence behavior has recently been demonstrated for the simplest continuous-time random walk [N. Konno, Phys. Rev. E 72, 026113 (2005)]. In this Brief Report, we use a different technique to establish the same convergence for a very large class of continuous-time quantum walks, and we identify the limit distribution in the general case.