Gravity from the extension of spatial diffeomorphisms

The possibility of the extension of spatial diffeomorphisms to a larger family of symmetries in a class of classical field theories is studied. The generator of the additional local symmetry contains a quadratic kinetic term and a potential term which can be a general (not necessarily local) functional of the metric. From the perspective of the foundation of Einstein's gravity our results are positive: The extended constraint algebra is either that of Einstein's gravity, or ultralocal gravity. If our goal is a simple modification of Einstein's gravity that for example makes it perturbatively renormalizable, as has recently been suggested, then our results show that there is no such theory within this class.Comment: 34 page

One-shot information-theoretical approaches to fluctuation theorems

Traditional thermodynamics governs the behaviour of large systems that evolve between states of thermal equilibrium. For these large systems, the mean values of thermodynamic quantities (such as work, heat and entropy) provide a good characterisation of the process. Conversely, there is ever-increasing interest in the thermal behaviour of systems that evolve quickly and far from equilibrium, and that are too small for their behaviour to be well-described by mean values. Two major fields of modern thermodynamics seek to tackle such systems: non-equilibrium thermodynamics, and the nascent field of one-shot statistical mechanics. The former provides tools such as fluctuation theorems, whereas the latter applies "one-shot" R\'enyi entropies to thermal contexts. In this chapter to the upcoming book "Thermodynamics in the quantum regime - Recent progress and outlook" (Springer International Publishing), I provide a gentle introduction to recent research that draws from both fields: the application of one-shot information theory to fluctuation theorems.Comment: As a chapter of: F. Binder, L. A. Correa, C. Gogolin, J. Anders, and G. Adesso (eds.), "Thermodynamics in the quantum regime - Recent progress and outlook", (Springer International Publishing

Determinantes del Tamaño de un Comité de Política Monetaria: Teoría y Evidencia de Corte Transversal

Estudios teóricos y empíricos desde la perspectiva de diferentes ciencias sugieren que un grupo de trabajo óptimo debería tener entre 5 y 9 miembros, aunque este número puede variar bajo diversas circunstancias y está bajo la influencia de factores propios al entorno en el que el grupo se desarrolla. Este trabajo presenta un modelo que analiza el tamaño de los comités de política monetaria (CPM) de 85 bancos centrales en función de los factores usuales o previstos por la literatura como los determinantes del tamaño óptimo de un comité. Los resultados sugieren que el número de miembros del CPM depende del tamaño de la zona monetaria de influencia, de las características propias a cada banco central y de diversas variables asociadas a la estabilidad macroeconómica del país. El tamaño de los CPMs de zonas monetarias grandes (Unión Europea, EEUU, Japón) parece estar cerca de su nivel “óptimo”, pero existen muchos países pequeños cuyos CPM se alejan de ese nivel.

Are there phase transitions in information space?

The interplay between two basic quantities -- quantum communication and information -- is investigated. Quantum communication is an important resource for quantum states shared by two parties and is directly related to entanglement. Recently, the amount of local information that can be drawn from a state has been shown to be closely related to the non-local properties of the state. Here we consider both formation and extraction processes, and analyze informational resources as a function of quantum communication. The resulting diagrams in information space allow us to observe phase-like transitions when correlations become classical.Comment: 4 pages, 3 epsi figures, to appear in Phys. Rev. Let

Evaporation limited loading of an atom trap

Recently, we have experimentally demonstrated a continuous loading mechanism for an optical dipole trap from a guided atomic beam [1]. The observed evolution of the number of atoms and temperature in the trap are consequences of the unusual trap geometry. In the present paper, we develop a model based on a set of rate equations to describe the loading dynamics of such a mechanism. We consider the collision statistics in the non-uniform trap potential that leads to twodimensional evaporation. The comparison between the resulting computations and experimental data allows to identify the dominant loss process and suggests ways to enhance the achievable steady-state atom number. Concerning subsequent evaporative cooling, we find that the possibility of controlling axial and radial confinement independently allows faster evaporation ramps compared to single beam optical dipole traps.Comment: 10 pages, 7 figure

Measurement and Particle Statistics in the Szilard Engine

A Szilard Engine is a hypothetical device which is able to extract work from a single thermal reservoir by measuring the position of particles within the engine. We derive the amount of work that can be extracted from such a device in the low temperature limit. Interestingly, we show this work is determined by the information gain of the initial measurement rather than by the number and type of particles which constitute the working substance. Our work provides another clear connection between information gain and extractable work in thermodynamical processes.Comment: 4 page

Nonequilibrium Detailed Fluctuation Theorem for Repeated Discrete Feedback

We extend the framework of forward and reverse processes commonly utilized in the derivation and analysis of the nonequilibrium work relations to thermodynamic processes with repeated discrete feedback. Within this framework, we derive a generalization of the detailed fluctuation theorem, which is modified by the addition of a term that quantifies the change in uncertainty about the microscopic state of the system upon making measurements of physical observables during feedback. As an application, we extend two nonequilibrium work relations: the nonequilibrium work fluctuation theorem and the relative-entropy work relation.Comment: 7 pages, 3 figure

A Thermodynamical Approach to Quantifying Quantum Correlations

We consider the amount of work which can be extracted from a heat bath using a bipartite state shared by two parties. In general it is less then the amount of work extractable when one party is in possession of the entire state. We derive bounds for this "work deficit" and calculate it explicitly for a number of different cases. For pure states the work deficit is exactly equal to the distillable entanglement of the state, and this is also achievable for maximally correlated states. In these cases a form of complementarity exists between physical work which can be extracted and distillable entanglement. The work deficit is a good measure of the quantum correlations in a state and provides a new paradigm for understanding quantum non-locality.Comment: 4 pages, Revtex4, title changed, caveat added to theore

Designing optimal discrete-feedback thermodynamic engines

Feedback can be utilized to convert information into useful work, making it an effective tool for increasing the performance of thermodynamic engines. Using feedback reversibility as a guiding principle, we devise a method for designing optimal feedback protocols for thermodynamic engines that extract all the information gained during feedback as work. Our method is based on the observation that in a feedback-reversible process the measurement and the time-reversal of the ensuing protocol both prepare the system in the same probabilistic state. We illustrate the utility of our method with two examples of the multi-particle Szilard engine.Comment: 15 pages, 5 figures, submitted to New J. Phy