# Work Extraction and Landauer's Principle in a Quantum Spin Hall Device

## TL;DR

This paper demonstrates how a quantum spin Hall device can utilize nuclear spins as a memory resource to extract work from heat, illustrating Landauer's principle and proposing an experimental setup for observation.

## Contribution

It introduces a method to use nuclear spins in a quantum spin Hall device for work extraction and Landauer erasure, linking thermodynamics with spintronics.

## Key findings

- Nuclear spins can serve as a memory resource for work extraction.
- Bias currents can initialize nuclear spins, demonstrating Landauer's principle.
- Proposed experimental setup for observing the cycle.

## Abstract

Landauer's principle states that erasure of each bit of information in a system requires at least a unit of energy $k_B T \ln 2$ to be dissipated. In return, the blank bit may possibly be utilized to extract usable work of the amount $k_B T \ln 2$, in keeping with the second law of thermodynamics. While in principle any collection of spins can be utilized as information storage, work extraction by utilizing this resource in principle requires specialized engines that are capable of using this resource. In this work, we focus on heat and charge transport in a quantum spin Hall device in the presence of a spin bath. We show how a properly initialized nuclear spin subsystem can be used as a memory resource for a Maxwell's Demon to harvest available heat energy from the reservoirs to induce charge current that can power an external electrical load. We also show how to initialize the nuclear spin subsystem using applied bias currents which necessarily dissipate energy, hence demonstrating Landauer's principle. This provides an alternative method of "energy storage" in an all-electrical device. We finally propose a realistic setup to experimentally observe a Landauer erasure/work extraction cycle.