Measurement-based quantum heat engine in a multilevel system

TL;DR

This paper compares quantum Otto engines using two cycle models and different multilevel working substances, revealing that complex systems and measurement protocols can enhance efficiency beyond traditional two-bath setups.

Contribution

It introduces a measurement-based quantum heat engine cycle and demonstrates its potential for higher efficiency with multilevel systems compared to standard models.

Findings

Complex working substances can achieve higher efficiencies.

Measurement-based protocols can outperform two-bath models.

Idle levels enable exploitation for efficiency gains.

Abstract

We compare quantum Otto engines based on two different cycle models: a two-bath model, with a standard heat source and sink, and a measurement-based protocol, where the role of heat source is played by a quantum measurement. We furthermore study these cycles using two different `working substances': a single qutrit (spin-1 particle) or a pair of qubits (spin-1/2 particles) interacting via the XXZ Heisenberg interaction. Although both cycle models have the same efficiency when applied on a single-qubit working substance, we find that both can reach higher efficiencies using these more complex working substances, by exploiting the existence of `idle' levels, i.e., levels that do not shift while the spins are subjected to a variable magnetic field. Furthermore, with an appropriate choice of measurement, the measurement-based protocol becomes more efficient than the two-bath model.