Experimental characterization of a spin quantum heat engine

TL;DR

This paper experimentally demonstrates a spin-based quantum heat engine using NMR, analyzing irreversibility and efficiency at the quantum scale, achieving near-thermodynamic-limit efficiency.

Contribution

It presents the first experimental realization of a quantum heat engine with detailed characterization of quantum and thermal fluctuations.

Findings

Achieved an efficiency of approximately 42% in the quantum heat engine.

Fully characterized irreversibility through energy fluctuation assessment.

Demonstrated operation close to the thermodynamic efficiency limit.

Abstract

Developments in the thermodynamics of small quantum systems envisage non-classical thermal machines. In this scenario, energy fluctuations play a relevant role in the description of irreversibility. We experimentally implement a quantum heat engine based on a spin-1/2 system and nuclear magnetic resonance techniques. Irreversibility at microscope scale is fully characterized by the assessment of energy fluctuations associated with the work and heat flows. We also investigate the efficiency lag related to the entropy production at finite time. The implemented heat engine operates in a regime where both thermal and quantum fluctuations (associated with transitions among the instantaneous energy eigenstates) are relevant to its description. Performing a quantum Otto cycle at maximum power, the proof-of-concept quantum heat engine is able to reach an efficiency for work extraction ($\eta\approx42$%) very close to its thermodynamic limit ($\eta=44$%).