The concept of quantum thermodynamic phase transfer (QTPT) proposes a new perspective on how thermodynamic transformations affect not only the entropy of a system but also its intrinsic quantum phase. In conventional thermodynamics, a process is often described solely by changes in macroscopic variables such as temperature, volume, and entropy. QTPT extends this view by introducing a phase variable φ_T that couples to thermodynamic forces during a transformation. This coupling is governed by a set of linear response relations that relate the change in φ_T to gradients of temperature and chemical potential, thereby unifying quantum coherence and classical thermodynamics within a single framework. The theory predicts measurable signatures in quantum heat engines and refrigerators, such as phase-dependent work output and entropy production that can be experimentally accessed through interferometric techniques. By offering a consistent description of how thermodynamic work can be harnessed to control quantum phases, QTPT opens pathways for designing high-efficiency quantum machines and for exploring fundamental limits of energy conversion in the quantum regime.
The concept of quantum thermodynamic phase transfer (QTPT) proposes a new perspective on how thermodynamic transformations affect not only the entropy of a system but also its intrinsic quantum phase. In conventional thermodynamics, a process is often described solely by changes in macroscopic variables such as temperature, volume, and entropy. QTPT extends this view by introducing a phase variable φ_T that couples to thermodynamic forces during a transformation. This coupling is governed by a set of linear response relations that relate the change in φ_T to gradients of temperature and chemical potential, thereby unifying quantum coherence and classical thermodynamics within a single framework. The theory predicts measurable signatures in quantum heat engines and refrigerators, such as phase-dependent work output and entropy production that can be experimentally accessed through interferometric techniques. By offering a consistent description of how thermodynamic work can be harnessed to control quantum phases, QTPT opens pathways for designing high-efficiency quantum machines and for exploring fundamental limits of energy conversion in the quantum regime.
In conventional thermodynamics, a macroscopic process is characterized by changes in thermodynamic variables such as temperature, pressure, and entropy. In quantum thermodynamics, the state of a system is described by a density operator ρ, and the entropy of the system is given by the von Neumann entropy S = -k_B Tr(ρ ln ρ). Recent theoretical investigations have suggested that quantum coherence and phase correlations can also be thermodynamically relevant. This paper introduces the concept of Quantum Thermodynamic Phase Transfer (QTPT), a formalism that treats the quantum phase φ_T as a thermodynamic variable that can change during a process. We propose a set of postulates that extend the first and second laws of thermodynamics to include a term that accounts for the work associated with changes in φ_T. The framework is illustrated with a simple two–level system coupled to a thermal bath and driven by a time–dependent phase. We derive expressions for the generalized free energy and the entropy production that include phase contributions. The implications of QTPT for quantum heat engines, quantum refrigeration, and the fundamental limits of quantum thermodynamic cycles are discussed. The potential for a Nobel–level recognition of the unification of quantum coherence with classical thermodynamic principles is highlighted.
After a brief historical introduction of quantum thermodynamics, we present its main goal and objectives, from fundamental questions to practical applications in quantum technologies. We then introduce the standard thermodynamic framework for quantum systems, valid in the weak coupling limit and in thermal environments. Extensions to strong coupling and nonthermal baths are briefly mentioned. Then, using this standard thermodynamic framework, we describe the quantum version of the Otto cycle and Carnot cycle for heat-to-work conversion as well as for refrigeration. The analysis of their differences is used to introduce the concept of entropy production at the quantum level, which quantifies irreversibility and is responsible for loss of efficiency. Then, we present a simple description of an autonomous quantum refrigerator, a promising device for qubit re-initialisation in quantum technologies. Finally, we briefly mention some quantum effects in heat engines and refrigerators. We conclude with a perspective on the main goals of quantum thermodynamics.
A central open question in quantum thermodynamics is the identification of thermodynamic entropy away from equilibrium. Although thermodynamic entropy coincides with the von Neumann entropy for a Gibbs state at equilibrium, the thermodynamic role of quantum coherence generated during nonequilibrium evolution remains unclear. Here, we show that von Neumann entropy does not, in general, represent the thermodynamic entropy governing heat exchange in coherent nonequilibrium quantum systems. By integrating the resource theory of quantum coherence with thermodynamic principles, we develop a general framework for nonequilibrium quantum thermodynamics. We identify thermodynamic entropy with the energy entropy derived from energy-measurement statistics and introduce a dynamical temperature extending the equilibrium concept to nonequilibrium states. Consequently, we obtain an exact entropy-balance relation separating the entropy flux associated with heat exchange from the coherence-loss contribution to entropy production, establishing an operational connection between quantum coherence, heat flow, and total entropy change. Unlike approaches relying on equilibrium reference states or stationary Gibbs ensembles, our framework uses instantaneous dynamical quantities and remains valid throughout transient nonequilibrium evolution. It provides consistent dynamical definitions of temperature, work, heat, and free energy. Applying the formalism to an exactly solvable open quantum system, we show that the first and second laws hold throughout transient evolution and that equilibrium thermodynamics emerges dynamically in the weak-coupling long-time limit. Our results establish a unified framework for coherent nonequilibrium quantum thermodynamics and suggest opportunities for controlling heat dissipation through coherence engineering in quantum thermal technologies.
This paper proposes a novel approach to quantum information transfer, termed "Quantum Entanglement Entropy Transfer (EET)." The core claim is that by precisely controlling the micro-scale entropy transfer between entangled particles, direct quantum information transmission can be achieved without relying on physical media, circumventing the limitations imposed by classical communication bottlenecks. The proposed mechanism utilizes non-classical thermodynamics and a specifically designed "entropy pump" system. This system leverages microscopic thermal fluctuations within entangled particles to facilitate non-local entropy transfer, thereby driving changes in the entanglement correlation between the particles. Mathematical formalism is presented to describe the entropy transfer process, highlighting the role of entanglement entropy and the thermodynamic parameters governing the system. The novelty of this approach lies in its utilization of entanglement as the primary medium for entropy transfer, coupled with the practical demands of quantum information transmission. The theoretical framework presented offers a potentially transformative pathway for quantum communication, moving beyond conventional approaches and opening avenues for ultra-fast, secure information transfer.
The control of open quantum systems and their associated quantum thermodynamic properties is a topic of growing importance in modern quantum physics and quantum chemistry research. This unique and self-contained book presents a unifying perspective of such open quantum systems, first describing the fundamental theory behind these formidably complex systems, before introducing the models and techniques that are employed to control their quantum thermodynamics processes. A detailed discussion of real quantum devices is also covered, including quantum heat engines and quantum refrigerators. The theory of open quantum systems is developed pedagogically, from first principles, and the book is accessible to graduate students and researchers working in atomic physics, quantum information, condensed matter physics, and quantum chemistry.
This paper proposes a novel framework for understanding and manipulating quantum coherence within thermodynamic systems. The core concept revolves around establishing a quantitative link between quantum coherence and thermodynamics, utilizing thermodynamic principles to guide the design and control of quantum systems. A new "quantum coherence thermodynamic potential" is defined, providing a framework to describe the evolution of coherence in quantum systems exposed to thermal environments. This potential allows for system optimization by considering the interplay between coherence preservation and thermal dissipation. The proposed approach offers a fundamentally new perspective on quantum system design, moving beyond purely phenomenological descriptions towards a thermodynamically grounded understanding. This work lays the groundwork for precise coherence control and offers a potential route toward harnessing quantum coherence for practical applications. The central equation describing the evolution of quantum coherence is presented as: ΔS = -Q / T where ΔS represents the change in quantum coherence, Q is the heat exchanged, and T is the absolute temperature. This equation highlights the fundamental relationship between coherence preservation and the thermal environment. Further derivations and expansions of this core equation are provided throughout the paper. ---