arXiv subjects

José A. Almanza-Marrero

Publications and source records attributed to José A. Almanza-Marrero.

3 recordsLinked to original sources

arXiv2026

Nonequilibrium thermodynamics of feedback-control: a phase-space perspective

Maxwell demons can convert knowledge into thermodynamic advantage by using measurement-acquired information. However, standard formulations of this problem assume that the demon has access to the system's entire phase space, an assumption that fails in many practical applications. Here, I address this problem by deriving fluctuation relations for general feedback-controlled systems, including such singular cases. The central quantity is a generalized notion of unavailable information: a portion of the acquired information that cannot be used to extract useful work. Finally, a Szilard engine with finite resolution illustrates these results. In the high-resolution limit, the information acquired by the demon may diverge, yet the extractable work remains finite. This work shows that this occurs because an equally divergent amount of information becomes unavailable.

cond-mat.stat-mech↗

arXiv2026

Pareto fronts and trade-off relations from exact multi-objective optimization of thermal machines

Thermal machines are physical systems that, when fueled by input energy, perform output tasks such as heat pumping or the production of work. Their performance is characterized with several, often competing quantities, such as power, efficiency, energy waste, and resilience to environmental noise. Multi-objective optimization provides a key tool to investigate the characterization of the best thermal machines operating in the irreversible linear-response regime. Here, we derive exact analytical parameterizations for the optimal (Pareto) fronts associated with any given choice of relative weights assigned to their mean extracted power $P$, efficiency $η$, entropy production $Σ$ and the amplitude of power fluctuations $σ^2_P$. The geometry of the front of endoreversible machines is universal: two-, three-, and four-objective trade-offs follow analytical formulae that do not depend on the value of any physical parameter of the machine. We show that such universal thermodynamic Pareto fronts also set quantitative fundamental limits for the performance of non-endoreversible machines. Furthermore, we demonstrate that our results apply to existing experimental data from different physical systems also beyond the linear regime, ranging from atomic to macroscopic scales, including single-atom engines, colloidal systems, macroscopic engines and power plants.

cond-mat.stat-mech↗

arXiv2025

Certifying quantum enhancements in thermal machines beyond the Thermodynamic Uncertainty Relation

Quantum coherence has been shown to impact the operational capabilities of quantum systems performing thermodynamic tasks in a significant way, and yet the possibility and conditions for genuine coherence-enhanced thermodynamic operation remain unclear. Introducing a comparison with classical machines using the same set of thermodynamic resources, we show that for steady-state quantum thermal machines -- both autonomous and externally driven -- that interact weakly with thermal reservoirs and work sources, the presence of coherence induced by perturbations in the machine Hamiltonian guarantees a genuine thermodynamic advantage under mild conditions. This advantage applies to both cases where the induced coherence is between levels with different energies or between degenerate levels. On the other hand, we show that engines subjected to noise-induced coherence can be outperformed by classical stochastic engines using exactly the same set of (incoherent) resources. We illustrate our results with three prototypical models of heat engines and refrigerators: the three-level amplifier, the three-qubit autonomous refrigerator, and a noise-induced-coherence machine.

quant-ph↗