Entropy production and fluctuations in a Maxwell's refrigerator with squeezing

Clarifying the impact of quantumness in the operation and properties of thermal machines represents a major challenge. Here we envisage a toy model acting either as an information-driven fridge or as heat-powered information eraser in which coherences can be naturally introduced in by means of squeezed thermal reservoirs. We study the validity of the transient entropy production fluctuation theorem in the model with and without squeezing as well as its decomposition into adiabatic and non-adiabatic contributions. Squeezing modifies fluctuations and introduces extra mechanisms of entropy exchange. This leads to enhancements in the cooling performance of the refrigerator, and to overcoming Landauer's bound in the setup.Comment: 10 pages, 2 figures; v2: small corrections and improvement

Autonomous thermal machine for amplification and control of energetic coherence

We present a model for an autonomous quantum thermal machine comprised of two qubits capable of manipulating and even amplifying the local coherence in a non-degenerate external system. The machine uses only thermal resources, namely, contact with two heat baths at different temperatures, and the external system has a non-zero initial amount of coherence. The method we propose allows for an interconversion between energy, both work and heat, and coherence in an autonomous configuration working in out-of-equilibrium conditions. This model raises interesting questions about the role of fundamental limitations on transformations involving coherence and opens up new possibilities in the manipulation of coherence by autonomous thermal machines.Comment: v1: 5 + 3 pages, 2 figures. v2: Restructured version with several new results and a new appendix, 11 + 14 pages, 4 + 3 figures. v3: Improved and corrected version with new discussions, 8 + 8 pages, 4 + 3 figure

Synchronization along quantum trajectories

We employ a quantum trajectory approach to characterize synchronization and phase-locking between open quantum systems in nonequilibrium steady states. We exemplify our proposal for the paradigmatic case of two quantum Van der Pol oscillators interacting through dissipative coupling. We show the deep impact of synchronization on the statistics of phase-locking indicators and other correlation measures defined for single trajectories, spotting a link between the presence of synchronization and the emergence of large tails in the probability distribution for the entanglement along trajectories. Our results shed new light on fundamental issues regarding quantum synchronization providing new methods for its precise quantification.Comment: v2: 9 + 3 pages, 5 figures. v3: few typos corrected, close to the published versio

Nonequilibrium potential and fluctuation theorems for quantum maps

We derive a general fluctuation theorem for quantum maps. The theorem applies to a broad class of quantum dynamics, such as unitary evolution, decoherence, thermalization, and other types of evolution for quantum open systems. The theorem reproduces well-known fluctuation theorems in a single and simplified framework and extends the Hatano-Sasa theorem to quantum nonequilibrium processes. Moreover, it helps to elucidate the physical nature of the environment inducing a given dynamics in an open quantum system.Comment: 10 page

Quantum fluctuation theorems for arbitrary environments: adiabatic and non-adiabatic entropy production

We analyze the production of entropy along non-equilibrium processes in quantum systems coupled to generic environments. First, we show that the entropy production due to final measurements and the loss of correlations obeys a fluctuation theorem in detailed and integral forms. Second, we discuss the decomposition of the entropy production into two positive contributions, adiabatic and non-adiabatic, based on the existence of invariant states of the local dynamics. Fluctuation theorems for both contributions hold only for evolutions verifying a specific condition of quantum origin. We illustrate our results with three relevant examples of quantum thermodynamic processes far from equilibrium.Comment: 20 pages + 6 of appendices; 7 figures; v2: New example added (example A) and some minor corrections; accepted in Phys. Rev.

The "despoblation" and "repoblation" of the Duero Valley: The problematic of the fonts and the historiography Debate

Si ya a priori los datos que tenemos sobre los siglos de la transición de la Antigüedad a la Edad Media son de por sí escuetos, oscuros y de difícil interpretación, esta situación se agrava conforme nos acercamos a los territorios bañados por el Cantábrico. Desde inicios del pasado siglo, varios fueron los debates que focalizaron la atención de los más prestigiosos medievalistas, tanto españoles, como peninsulares, como europeos. Entre estos debates, destacaron los estudios sobre los orígenes y significación del feudalismo, la transición entre la Antigüedad y el Medievo o el papel que jugaron las sociedades septentrionales y mozárabes en estos procesos. Nosotros centraremos nuestra atención en otras dos polémicas: La situación en que quedó el espacio geográfico en el que se desarrolló la acción histórica y la referida a las fuentes para el conocimiento de estos siglosIf a priori the dates we’ve got about the centuries of the transition for the Antiquity to the Middle Ages are shorts, darks and difficult to interpret, this situation worsens as we approach to the territories bathed by the Cantabric. Since early last century, there were several discussions that focused the attention of the most prestigious medievalists, Spanish, Peninsular and Europeans. Among these mentioned discussions, highlighted the studies about the origins and signification of the feudalism, the transition between the Antiquity and the Middle Ages or the paper played by the northern and mozarabic societies in these processes. We’ll focus our attention in other two polemics: The situation in which stayed the geographical space where the historic action were developed; and the aforementioned to the sources for these centuries knowledg

Quantum-enhanced performance in superconducting Andreev-reflection engines

When a quantum dot is attached to a metallic reservoir and a superconducting contact Andreev processes leads to a finite subgap current at the normal lead and the creation or destruction of Cooper pairs. Andreev-reflection engines profit from the destruction of Cooper pairs to provide the work needed to set a charge current at the normal-conductor contact generating electrical power. For this power-transduction device high power and large efficiencies in quantum-mechanically enhanced regimes are demonstrated. There thermodynamic trade-off relations between power, efficiency and stability, valid for any classical engine are overcome, and kinetic constraints on the engine precision are largely surpassed in arbitrary far from equilibrium conditions.Comment: 5 + 5 pages, 3 Figures. v2: minor changes. Accepted in Physical Review Researc

Synchronization, quantum correlations and entanglement in oscillator networks

Synchronization is one of the paradigmatic phenomena in the study of complex systems. It has been explored theoretically and experimentally mostly to understand natural phenomena, but also in view of technological applications. Although several mechanisms and conditions for synchronous behavior in spatially extended systems and networks have been identified, the emergence of this phenomenon has been largely unexplored in quantum systems until very recently. Here we discuss synchronization in quantum networks of different harmonic oscillators relaxing towards a stationary state, being essential the form of dissipation. By local tuning of one of the oscillators, we establish the conditions for synchronous dynamics, in the whole network or in a motif. Beyond the classical regime we show that synchronization between (even unlinked) nodes witnesses the presence of quantum correlations and entanglement. Furthermore, synchronization and entanglement can be induced between two different oscillators if properly linked to a random network.Comment: 10 pages, 5 figures, submitted to Scientific Report