Quantum ratchet transport with minimal dispersion rate

TL;DR

This paper investigates quantum ratchet transport by analyzing wave packet dynamics in a periodically modulated potential, focusing on optimizing directed motion while minimizing wave packet dispersion.

Contribution

It introduces a quantum Péclet number to quantify and optimize the balance between directed velocity and dispersion in quantum ratchet systems.

Findings

Quantum ratchet transport can be controlled by symmetry-breaking modulation.

A quantum Péclet number effectively characterizes transport quality.

Optimal transport involves high velocity and low dispersion.

Abstract

We analyze the performance of quantum ratchets by considering the dynamics of an initially localized wave packet loaded into a flashing periodic potential. The directed center-of-mass motion can be initiated by the uniform modulation of the potential height, provided that the modulation protocol breaks all relevant time- and spatial reflection symmetries. A poor performance of quantum ratchet transport is characterized by a slow net motion and a fast diffusive spreading of the wave packet, while the desirable optimal performance is the contrary. By invoking a quantum analog of the classical P\'eclet number, namely the quotient of the group velocity and the dispersion of the propagating wave packet, we calibrate the transport properties of flashing quantum ratchets and discuss the mechanisms that yield low-dispersive directed transport.