A Coupled Quantum Otto Cycle

TL;DR

This paper investigates a quantum heat engine based on a two-spin Heisenberg model undergoing an Otto cycle, revealing conditions for enhanced efficiency and novel parameter regimes beyond uncoupled systems.

Contribution

It introduces a coupled quantum Otto cycle with conditions for higher efficiency and identifies new parameter domains not accessible in interaction-free models.

Findings

Engine efficiency can surpass that of uncoupled models under certain conditions.

A tighter upper bound on efficiency than the Carnot limit is established.

A new parameter domain enables improved quantum heat engine performance.

Abstract

We study the 1-d isotropic Heisenberg model of two spin-1/2 systems as a quantum heat engine. The engine undergoes a four-step Otto cycle where the two adiabatic branches involve changing the external magnetic field at a fixed value of the coupling constant. We find conditions for the engine efficiency to be higher than the uncoupled model; in particular, we find an upper bound which is tighter than the Carnot bound. A new domain of parameter values is pointed out which was not feasible in the interaction-free model. Locally, each spin seems to effect the flow of heat in a direction opposite to the global temperature gradient. This seeming contradiction to the second law can be resolved in terms of local effective temperature of the spins.