Upper bounds on quantum dynamics in arbitrary dimension

TL;DR

This paper introduces a new method to establish upper bounds on quantum transport in multi-dimensional operators, extending previous one-dimensional results to higher dimensions without excluding phases.

Contribution

The authors develop a general approach to bound quantum dynamics in arbitrary dimensions, applicable to Schrödinger and long-range operators, and provide the first phase-uniform results for quasiperiodic operators beyond one dimension.

Findings

Power-logarithmic bounds on quantum transport for multidimensional operators

Results hold uniformly for all phases and Diophantine frequencies

Applicable to various ergodic operators, including skew-shift dynamics

Abstract

Motivated by the research on upper bounds on the rate of quantum transport for one-dimensional operators, particularly, the recent works of Jitomirskaya--Liu and Jitomirskaya--Powell and the earlier ones of Damanik--Tcheremchantsev, we propose a method to prove similar bounds in arbitrary dimension. The method applies both to Schroedinger and to long-range operators. In the case of ergodic operators, one can use large deviation estimates for the Green function in finite volumes to verify the assumptions of our general theorem. Such estimates have been proved for numerous classes of quasiperiodic operators in one and higher dimension, starting from the works of Bourgain, Goldstein, and Schlag. One of the applications is a power-logarithmic bound on the quantum transport defined by a multidimensional discrete Schr\"odinger (or even long-range) operator associated with an irrational shift, valid for all Diophantine frequencies and uniformly for all phases. To the best of our knowledge, these are the first results on the quantum dynamics for quasiperiodic operators in dimension greater than one that do not require exclusion of a positive measure of phases. Moreover, and in contrast to localisation, the estimates are uniform in the phase. The arguments are also applicable to ergodic operators corresponding to other kinds of base dynamics, such as the skew-shift.