Quantum Heat Engine Achieves Higher Efficiency with Three-Stroke Isochoric Cycle in Graphene Systems

The pursuit of efficient nanoscale engines drives innovation in fields ranging from energy harvesting to advanced materials, and a team led by Hadi Mohammed Soufy and Colin Benjamin from the National Institute of Science Education and Research now presents a significant advance in this area. They demonstrate a novel three-stroke quantum isochoric heat engine that outperforms both classical engine designs and recently proposed quantum cycles, achieving higher efficiency with a simplified operational structure. This engine operates by confining a particle within a one-dimensional potential well, and the researchers extend their analysis to explore its performance in various graphene systems, including monolayer and bilayer configurations. Notably, magic-angle twisted bilayer graphene emerges as the most promising material for this engine, suggesting a pathway towards realising highly efficient nanoscale devices with practical applications.

Graphene Heat Engine via Quantum Isochoric Cycle

Researchers have developed a three-stroke quantum isochoric cycle functioning as a heat engine between two thermal reservoirs. This cycle, maintained at constant volume, utilises a working substance confined within an infinite potential well, allowing for precise control over energy levels. The team investigated the engine’s performance using magic-angle twisted bilayer graphene as a realistic material, demonstrating its potential for practical application. Calculations reveal this engine achieves a maximum efficiency of 0. 60, significantly exceeding the theoretical limit for a two-level system. By varying system parameters like temperature and magnetic field, the study explores how to optimise the engine’s power output and efficiency, establishing a novel framework for designing high-efficiency quantum heat engines using readily available materials and controllable quantum systems.

The cycle’s performance was benchmarked against classical three-stroke triangular and isochoric engines, and also compared to a recently proposed three-stroke quantum isoenergetic cycle. The quantum isochoric cycle demonstrated higher efficiency than both classical counterparts. Its reduced number of strokes substantially lowers control complexity in nanoscale thermodynamic devices, offering a more feasible route to experimental realisation compared to conventional four-stroke architectures. Researchers further evaluated the cycle in graphene-based materials under magnetic fields, revealing significant performance variations.

Graphene Heterostructures as Quantum Otto Engines

This research explores the potential of graphene materials, including monolayer, bilayer, twisted bilayer, and magic-angle twisted bilayer graphene, as highly efficient quantum Otto engines. Researchers focused on how external magnetic fields can control energy levels and optimise engine efficiency. The study highlights magic-angle twisted bilayer graphene (MATBG), with a 1. 05° twist angle, as the most promising material due to its flat bands, low energy levels, and uniform electron occupation probabilities, all contributing to enhanced thermodynamic performance.

The team proposes and analyses a three-stroke thermodynamic cycle tailored for graphene heterostructures, designed to maximise work output and efficiency. Applying a magnetic field allows for precise control over energy levels and optimisation of the cycle. The study compares the efficiency of the quantum Otto engine using different graphene materials, demonstrating that MATBG significantly outperforms monolayer, bilayer, and twisted bilayer graphene. Key performance metrics, including power, efficiency, and work output, were used to evaluate the engine’s performance.

The research relies heavily on theoretical modelling and calculations based on quantum mechanics and thermodynamics. Landau level calculations determine the energy levels of electrons in the graphene materials under a magnetic field, and occupation probabilities are calculated using the Fermi-Dirac distribution. The three-stroke thermodynamic cycle is analysed to determine work output, heat exchange, and efficiency. Computational tools and programming languages were used to perform the calculations and simulations, with code available for reproducibility.

Graphene Heat Engines and Isochoric Cycle Efficiency

This work introduces a three-stroke quantum isochoric cycle functioning as a heat engine between two thermal reservoirs, and demonstrates its superior performance compared to classical engines and a previously proposed quantum isoenergetic cycle. Researchers established this advantage using a particle confined within a one-dimensional infinite potential well as a foundational system, then extended the analysis to various graphene-based platforms subjected to magnetic fields, including monolayer, bilayer, and twisted bilayer graphene. Notably, magic-angle twisted bilayer graphene (MATBG) consistently achieved the highest efficiency at a given work output, attributed to a smaller cycle area resulting in reduced heat absorption and rejection. This finding highlights the potential of engineered quantum materials, particularly those with tunable flat-band electronic structures, for developing high-performance quantum thermodynamic devices. The reduced operational complexity of this three-stroke cycle, coupled with its potential for quantum-enhanced performance, positions it as a promising avenue for probing and exploiting thermodynamic behaviour in complex quantum materials and understanding microscopic energy conversion mechanisms.