title: Quantum to classical transition for random walks.
abstract: We look at two possible routes to classical behavior for the discrete quantum random walk on the integers: decoherence in the quantum "coin" which drives the walk, or the use of higher-dimensional (or multiple) coins to dilute the effects of interference. We use the position variance as an indicator of classical behavior and find analytical expressions for this in the long-time limit; we see that the multicoin walk retains the "quantum" quadratic growth of the variance except in the limit of a new coin for every step, while the walk with decoherence exhibits "classical" linear growth of the variance even for weak decoherence.
authors.affiliation: Institute for Advanced Study, Einstein Drive, Princeton, New Jersey 08540, USA. tbrun@ias.edu
authors.forename: Todd A
authors.initials: TA
authors.lastname: Brun
authors.forename: Hilary A
authors.initials: HA
authors.lastname: Carteret
authors.forename: Andris
authors.initials: A
authors.lastname: Ambainis