The extraction of work from quantum coherence (1506.07875v2)

Abstract: The interplay between quantum-mechanical properties, such as coherence, and classical notions, such as energy, is a subtle topic at the forefront of quantum thermodynamics. The traditional Carnot argument limits the conversion of heat to work; here we critically assess the problem of converting coherence to work. Through a careful account of all resources involved in the thermodynamic transformations within a fully quantum-mechanical treatment, we show that there exist thermal machines extracting work from coherence arbitrarily well. Such machines only need to act on individual copies of a state and can be reused. On the other hand, we show that for any thermal machine with finite resources not all the coherence of a state can be extracted as work. However, even bounded thermal machines can be reused infinitely many times in the process of work extraction from coherence.

• The paper proposes that thermal machines can extract work from quantum coherence, suggesting such machines can act on individual quantum states efficiently and be reused.
• The research identifies that while theoretical work extraction from coherence is possible, practical limits exist when considering finite resources.
• The study highlights the critical role of quantum reference systems in facilitating coherence manipulation and work extraction within thermal machines.

Extraction of Work from Quantum Coherence: A Formal Examination

The paper "The extraction of work from quantum coherence," authored by Korzekwa et al., delves deeply into the interactions between quantum coherence and classical thermodynamic work. This work is nestled within the expanding field of quantum thermodynamics and seeks to quantify how quantum mechanical properties can be harnessed to extract work, a concept traditionally governed by classical thermodynamic laws.

The exploration begins by stating the foundational concepts upon which quantum thermodynamics rests—quantum coherence and classical energy notions. The authors challenge the classical Carnot limitations regarding converting heat to work by proposing scenarios in which quantum coherence serves as an additional resource for work extraction.

Main Contributions

1. Thermal Machines and Coherence Utilization: The authors propose that thermal machines, which are devices designed to manipulate thermodynamical systems at the quantum level, can effectively extract work from quantum coherence. Their findings suggest that such machines can selectively act on individual quantum states and can be reused indefinitely, which adds a significant layer of efficiency to these devices.
2. Boundaries of Coherence-Based Work Extraction: The paper makes a clear distinction between the theoretical possibility and practical limitations of coherence-based work extraction. While it posits that a thermal machine can utilize coherence to extract work, there is a boundary when finite resources are considered.
3. Role of Quantum Reference Systems: The research shows that ancillary systems, referred to as reference systems with quantum coherence, are critical in these processes. These references can facilitate coherence manipulation in thermal machines, provided they are adequately maintained, without degrading over time.

Numerical and Theoretical Results

The authors present strong numerical results supporting their theoretical claims. They show how quantum coherence can be systematically converted into work—up to a certain limit—by maintaining a coherent quantum reference. However, the paper emphasizes that all available quantum coherence cannot entirely be transformed into work when finite resources are considered, setting a ceiling for practical applications of this theory.

Implications and Future Considerations

Korzekwa et al.’s research gives rise to several important implications and future directions for the field of quantum thermodynamics. Firstly, it underscores the need for innovative designs of thermal machines that can efficiently utilize quantum resources without depletion. Secondly, it proposes new avenues for quantum technology, especially in information processing, where quantum coherence could harness additional work resources leading to more energy-efficient processes.

On a theoretical level, the research underscores the need for a comprehensive framework in quantum thermodynamics that reconciles the quantum-classical divide. With particular emphasis on the resource-accounting aspect of coherence, the paper calls for a structured approach to understand the interplay between quantum state coherence and how it can be practically utilized at macroscopic levels.

In conclusion, the paper "The extraction of work from quantum coherence" represents a significant stride in understanding how coherence in quantum systems can be a viable resource for extracting work. While laying down the theoretical bedrock and addressing practical limitations, the authors present a foundation on which future quantum thermodynamic technologies can be constructed and optimized, pushing the envelope of both quantum information science and classical thermodynamic principles.