title: Quantum transport and spin dynamics on shearless tori.
abstract: We investigate quantum dynamics in phase-space regions containing "shearless tori." We show that the properties of these peculiar classical phase-space structures-important to the dynamics of tokamaks-may be exploited for quantum information applications. In particular we show that shearless tori permit the nondispersive transmission of localized wave packets. The quantum many-body Hamiltonian of a Heisenberg ferromagnetic spin chain, subjected to an oscillating magnetic field, can be reduced to a classical one-body "image" dynamical system which is the well-studied Harper map. The Harper map belongs to a class of Hamiltonian systems (nontwist maps) which contain shearless tori. We show that a variant with sinusoidal time driving "driven Harper model" produces shearless tori which are especially suitable for quantum state transfer. The behavior of the concurrence is investigated as an example.
authors.affiliation: Department of Applied Physics, Graduate School of Engineering, Osaka City University, Osaka 558-8585, Japan. kudo.kazue@ocha.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Kudo
authors.forename: T S
authors.initials: TS
authors.lastname: Monteiro