title: Shape of the quantum diffusion front.
abstract: We show that quantum diffusion has well-defined front shape. After an initial transient, the wave packet front (tails) is described by a stretched exponential P(x,t) = A(t)exp(-absolute value of [x/w](gamma)), with 1 < gamma < infinity, where w(t) is the spreading width which scales as w(t) approximately t(beta), with 0 < beta < or = 1. The two exponents satisfy the universal relation gamma = 1/(1-beta). We demonstrate these results through numerical work on one-dimensional quasiperiodic systems and the three-dimensional Anderson model of disorder. We provide an analytical derivation of these relations by using the memory function formalism of quantum dynamics. Furthermore, we present an application to experimental results for the quantum kicked rotor.
authors: Department of Physics, University of Texas, Austin 78712, USA.
authors: J
authors: J
authors: Zhong
authors: R B
authors: RB
authors: Diener
authors: D A
authors: DA
authors: Steck
authors: W H
authors: WH
authors: Oskay
authors: M G
authors: MG
authors: Raizen
authors: E W
authors: EW
authors: Plummer
authors: Z
authors: Z
authors: Zhang
authors: Q
authors: Q
authors: Niu