Quantum Heat Engine Exceeds Classical Limits Using Noisy Coherence.

A quantum heat engine operating under Otto cycle conditions utilises coherence to exceed classical efficiency limits. Leggett-Garg correlations confirm non-classical behaviour, with amplitude damping reducing performance while phase damping has minimal impact. A quantifiable link between energy use and information processing within the engine was established.

The pursuit of efficient energy conversion remains a central challenge in physics and engineering. Recent research explores the potential of quantum mechanics to enhance the performance of heat engines, devices that convert thermal energy into useful work. A team led by Freddier Cuenca-Montenegro, Marcela Herrera, and John H. Reina, all affiliated with the Centre for Bioinformatics and Photonics—CIBioFi and the Departamento de Física at Universidad del Valle, detail their investigation into how quantum coherence – a fundamental property of quantum systems – can be harnessed to exceed the limitations of classical heat engines. Their work, entitled ‘Markovian heat engine boosted by quantum coherence’, demonstrates that a single-qubit engine operating under specific conditions can surpass classical efficiency limits by utilising the coherence present in noisy quantum states, while also quantifying the energetic cost of implementing such a device in a realistic circuit.

Quantum Heat Engines Demonstrate Efficiency Beyond Classical Limits

Recent investigations have revealed that quantum heat engines can, under specific conditions, exceed the thermodynamic efficiency limits established for their classical counterparts. This enhancement stems from the exploitation of quantum coherence – a fundamental property of quantum systems where multiple states can exist simultaneously – within the engine’s operational cycle.

Researchers focused on a single-qubit heat engine operating on the Otto cycle—a thermodynamic cycle that describes the functioning of many internal combustion engines. Simulations demonstrate that this quantum engine can surpass classical efficiency boundaries by actively utilising coherence present even in noisy initial states. The non-classical operation of the engine was confirmed through the observation of Leggett-Garg temporal correlations—a quantum phenomenon that demonstrates measurements at specific points in time can reveal correlations stronger than those permitted by classical physics.

The study identified a pronounced sensitivity to amplitude damping – a type of quantum decoherence where the probability amplitude of a quantum state diminishes over time. Amplitude damping significantly reduced both the engine’s efficiency and the amount of work it could extract. Conversely, phase damping – another decoherence mechanism affecting the relative phase between quantum states – had a negligible impact on performance.

To assess practical viability, researchers implemented a comprehensive simulation incorporating realistic noise channels, modelling the imperfections inherent in real-world quantum systems. This approach enabled a more accurate evaluation of engine performance under conditions that closely mimic those found in a laboratory setting.

Furthermore, the research introduces a novel operational measure quantifying the thermodynamic cost of the quantum circuit itself. This metric establishes a direct link between the energy consumed by the quantum hardware and the information processing it performs, providing valuable insight into the energetic demands of quantum technologies. Future work will explore the potential of more complex quantum engines and investigate the effects of different noise types on engine performance. This research represents a step towards realising practical quantum heat engines capable of outperforming classical counterparts, and could have implications for areas such as refrigeration and energy storage.