Fractional Control Gates Enable Quantum Engines with 84% to 100% Efficiency and Correlated Work Production

The pursuit of efficient quantum heat engines drives innovation in quantum technologies, and recent work by Elliot John Fox from the University of York, Taysa Mendes de Mendonça from the Universidade de São Paulo, Ferdinand Schmidt-Kaler and Irene D’Amico demonstrates a promising new approach using fractional control gates. These gates, which allow for precisely paced quantum operations, form the basis of circuits designed to maximise work production and overall engine efficiency. The team’s investigations reveal that maintaining coherence in one of the qubits significantly boosts the amount of work generated, achieving efficiencies ranging from 84% to 100% across various circuit designs. Importantly, the research also establishes a strong link between work output and the presence of quantum correlations within the engine’s working medium, offering valuable insight into optimising these emerging technologies.

Nth-root gates enable a carefully paced application of quantum control, crucial for optimising the performance of quantum engines. Researchers investigate fractional control gate protocols, extending beyond conventional implementations to achieve finer control over quantum systems. This work focuses on developing and analysing protocols that utilise fractional control gates, enabling precise manipulation of quantum states and enhancing engine efficiency. The team demonstrates that these fractional protocols offer significant advantages in tailoring the engine’s dynamics, specifically in scenarios where precise control over the working substance is paramount. Through theoretical analysis and numerical simulations, the researchers establish that fractional control gates provide a pathway to optimise quantum engine performance, surpassing the limitations of traditional control schemes and opening new avenues for quantum thermodynamics.

The application of two-qubit operations drives quantum thermodynamic protocols for operating a quantum heat engine. The team compared circuits utilising two and three qubits, considering maximum work production and related efficiency. The results show that, for all circuits considered and most initial conditions, quantum coherence of one of the qubits strongly increases the maximum work production and improves the system’s performance as a quantum heat engine. In these circuits, coherence is initially imprinted into one of the qubits, improving the overall maximum extractable work. Work gets generated with efficiencies ranging from 84% to 100%. Furthermore, the team uncovered a strong linear correlation.

Quantum Heat Engines And Thermodynamic Cycles

This collection represents a comprehensive overview of research related to quantum thermodynamics, quantum information, and related topics. It covers a wide range of approaches to building and analysing quantum heat engines, exploring various engine cycles, including Otto, Stirling, and Carnot-like cycles adapted for the quantum realm. The research investigates engines based on diverse quantum systems, such as spin systems, Rydberg atoms, superconducting qubits, and trapped ions. A significant portion of the research focuses on improving engine performance through enhancements like coherence, entanglement, non-equilibrium dynamics, optimal control, and the use of negative temperatures.

Researchers also study fluctuations and statistics to understand the statistical behaviour of quantum heat engines, and explore quantum batteries as devices for storing energy using quantum effects. The collection highlights the close relationship between quantum information and thermodynamics, demonstrating the role of quantum concepts in understanding and improving quantum engines. Measures like quantum discord, entanglement of formation, and coherence are explored as resources for enhancing engine performance. The collection also focuses on the practical aspects of building and controlling quantum heat engines, including the design of optimal quantum gates and pulse shaping techniques.

Researchers address the challenges of decoherence and errors in quantum systems, and explore implementations on various platforms, including superconducting qubits, trapped ions, and Rydberg atoms. The collection covers the more fundamental theoretical aspects of quantum thermodynamics, including fluctuation theorems, Gibbs formula, and thermodynamic proofs. It also analyses stroboscopic processes, which examine systems driven by time-periodic forces. A key observation is the strong interplay between quantum information and thermodynamics, where quantum information concepts are actively explored as resources for improving engine performance.

The research aims to demonstrate that quantum heat engines can outperform their classical counterparts, which would have significant implications for energy technology. The diversity of platforms used in the research is also noteworthy, allowing researchers to explore different approaches and overcome the limitations of any single platform. In summary, this collection provides a comprehensive snapshot of the current state of research in quantum thermodynamics and related fields. It highlights the exciting potential of harnessing quantum effects to improve energy technology and deepen our understanding of the fundamental laws of physics. It is a valuable resource for anyone interested in this rapidly evolving field.

Quantum Heat Engines and Negative Correlations

This research demonstrates that carefully designed sequences of quantum operations, specifically those employing nth-root gates, can function as effective heat engines, generating work with efficiencies ranging from 84% to 100%. The team investigated two and three-qubit circuits and found that introducing coherence into one of the qubits consistently enhances maximum work production across all tested configurations. Importantly, the results reveal a strong linear correlation between the amount of work generated and the development of negative correlations within the quantum system, suggesting a fundamental link between these two phenomena. Further analysis indicates that classical correlations generally play a more significant role in work production than total correlations, as measured by mutual information.

While both quantities are correlated, the team observed that generating work consistently leads to the creation of classical correlations between the components of the quantum working medium. The study acknowledges that the relationship between work and mutual information is more complex, particularly in the three-qubit Case 2 protocol, where the correlation is weaker. Future research could focus on disentangling the individual contributions of classical and quantum correlations to better understand and optimise work extraction in these quantum systems, potentially leading to more efficient quantum heat engines.