Increasing extractable work in small qubit landscapes

TL;DR

This paper explores how small quantum systems, specifically qubits, can maintain high free-energy states and increase extractable work through restricted dynamics, initial conditions, and correlations, revealing minimal system sizes and landscape features that facilitate this.

Contribution

It identifies the minimal qubit system size for increasing extractable work and demonstrates how landscape connectivity and initial temperature distribution influence work extraction.

Findings

Four qubits are the minimal system for increasing extractable work.

Restricted connectivity and inhomogeneous initial temperatures extend work-increasing intervals.

Correlations enable positive changes in extractable work.

Abstract

An interesting class of physical systems, including those associated with life, demonstrates the ability to hold thermalization at bay and perpetuate states of high free-energy compared to a local environment. In this work, we study quantum systems with no external sources or sinks for energy, heat, work, or entropy, that allow for high free-energy subsystems to form and persist. We initialize systems of qubits in mixed, uncorrelated states and evolve them subject to a conservation law. We find that four qubits make up the minimal system for which these restricted dynamics and initial conditions allow an increase in extractable work for a subsystem. On landscapes of eight co-evolving qubits, interacting in randomly selected subsystems at each step, we demonstrate that restricted connectivity and an inhomogeneous distribution of initial temperatures both lead to landscapes with longer intervals of increasing extractable work for individual qubits. We demonstrate the role of correlations that develop on the landscape in enabling a positive change in extractable work.