Diffusive spin transport

TL;DR

This paper presents a unified framework for understanding diffusive spin transport, combining spin decoherence in fluctuating magnetic fields with particle diffusion due to impurities, relevant for quantum information and mesoscopic systems.

Contribution

It introduces a comprehensive description of diffusive spin transport by integrating spin decoherence and spatial diffusion dynamics.

Findings

Characterizes spin decoherence using irreducible representations of the rotation group.

Describes diffusive dynamics of particles due to impurities.

Provides a unified model applicable to electronic devices and photon propagation.

Abstract

Information to be stored and transported requires physical carriers. The quantum bit of information (qubit) can for instance be realised as the spin 1/2 degree of freedom of a massive particle like an electron or as the spin 1 polarisation of a massless photon. In this lecture, I first use irreducible representations of the rotation group to characterise the spin dynamics in a least redundant manner. Specifically, I describe the decoherence dynamics of an arbitrary spin S coupled to a randomly fluctuating magnetic field in the Liouville space formalism. Secondly, I discuss the diffusive dynamics of the particle's position in space due to the presence of randomly placed impurities. Combining these two dynamics yields a coherent, unified picture of diffusive spin transport, as applicable to mesoscopic electronic devices or photons propagating in cold atomic clouds.