Nonadiabatic single-qubit quantum Otto engine

TL;DR

This paper analyzes a quantum Otto engine with a single qubit, exploring its operation modes, finite-time dynamics, and experimental implementation, highlighting non-adiabatic effects and oscillations affecting performance.

Contribution

It provides a detailed theoretical and experimental analysis of a non-adiabatic single-qubit quantum Otto engine, including finite-time effects and realistic implementation challenges.

Findings

Identification of four operation modes: heat engine, refrigerator, thermal accelerator, heater

Observation of oscillations in power due to Landau-Zener tunneling at low temperatures

Non-adiabatic effects impact the robustness of the engine's operation

Abstract

According to Clausius formulation of the second law of thermodynamics, for any thermal machine withdrawing heats $Q_{1,2}$ from two heat reservoirs at temperatures $T_{1,2}$, it holds $Q_1/T_1+Q_2/T_2 \leq 0$. Combined with the observation that the quantity $Q_1+Q_2$ is the work $W$ done by the system, that inequality tells that only 4 possible operation modes are possible for the thermal machine, namely heat engine [E], refrigerator [R], thermal accelerator [A] and heater [H]. We illustrate their emergence in the finite time operation of a quantum Otto engine realised with a single qubit. We first focus on the ideal case when isothermal and thermally-insulated strokes are well separated, and give general results as well as results pertaining to the specific finite-time Landau-Zener dynamics. We then present realistic results pertaining to the solid-state experimental implementation proposed by Karimi and Pekola [Phys. Rev. B \textbf{94} (2016) 184503]. That device is non-adiabatic both in the quantum mechanical sense and in the thermodynamical sense. Oscillations in the power extracted from the baths due to coherent LZ tunnelling at too low temperatures are observed that might hinder the robustness of the operation of the device against experimental noise on the control parameters.