Improving Performance of Quantum Heat Engines using modified Otto cycle

TL;DR

This paper proposes a modified Otto cycle for quantum heat engines that enhances efficiency by allowing the system to evolve freely to reach less excited states, improving work output especially near critical points.

Contribution

It introduces a novel modification to the quantum Otto cycle by incorporating a free evolution step, demonstrated on integrable and non-integrable models, to boost efficiency.

Findings

Modified cycle increases work output and efficiency.

Optimal free evolution time can be analytically determined.

Significant improvements observed near critical points.

Abstract

The efficiency of a quantum heat engine is maximum when the unitary strokes are adiabatic. On the other hand, this may not be always possible due to small energy gaps in the system, especially at the critical point where the gap vanishes. With the aim to achieve this adiabaticity, we modify one of the unitary strokes of the cycle by allowing the system to evolve freely with a particular Hamiltonian till a time so that the system reaches a less excited state. This will help in increasing the magnitude of the heat absorbed from the hot bath so that the work output and efficiency of the engine can be increased. We demonstrate this method using an integrable model and a non-integrable model as the working medium. In the case of a two spin system, the optimal value for the time till which the system needs to be freely evolved is calculated analytically in the adiabatic limit. The results show that implementing this modified stroke significantly improves the work output and efficiency of the engine, especially when it crosses the critical point.