Hyperaccurate thermoelectric currents

Thermodynamic currents, such as energy, heat, and entropy production, can fluctuate significantly at the nanoscale. However, some fluctuate less than others. Hyperaccurate currents are defined as those which fluctuate the least, in the sense that they maximize the signal-to-noise ratio (precision). In this Letter we analytically determine what are the hyperaccurate currents in quantum thermoelectrics, modeled by coherent transport in the Landauer-Büttiker formalism. Our results yield a tight and general bound on precision, which replace the classical thermodynamic uncertainty relations, that can be violated in quantum thermoelectrics. They also allow us to address the question of how close to hyperaccurate is a given current. We illustrate our findings for smooth boxcar functions, and for a double quantum dot operating as a thermal machine. In the latter, we use our results to establish the parameter ranges for which the output power of an autonomous engine can become hyperaccurate arbitrarily far from equilibrium

Joint fluctuation theorems for sequential heat exchange

We study the statistics of heat exchange of a quantum system that collides sequentially with an arbitrary number of ancillas. This can describe, for instance, an accelerated particle going through a bubble chamber. Unlike other approaches in the literature, our focus is on the \emph{joint} probability distribution that heat $Q_1$ is exchanged with ancilla 1, heat $Q_2$ is exchanged with ancilla 2, and so on. This allows one to address questions concerning the correlations between the collisional events. The joint distribution is found to satisfy a Fluctuation theorem of the Jarzynski-W\'ojcik type. Rather surprisingly, this fluctuation theorem links the statistics of multiple collisions with that of independent single collisions, even though the heat exchanges are statistically correlated

Energy barriers between metastable states in first-order quantum phase transitions

A system of neutral atoms trapped in an optical lattice and dispersively coupled to the field of an optical cavity can realize a variation of the Bose-Hubbard model with infinite-range interactions. This model exhibits a first-order quantum phase transition between a Mott insulator and a charge density wave, with spontaneous symmetry breaking between even and odd sites, as was recently observed experimentally [Landig, Nature (London) 532, 476 (2016)10.1038/nature17409]. In the present paper, we approach the analysis of this transition using a variational model which allows us to establish the notion of an energy barrier separating the two phases. Using a discrete WKB method, we then show that the local tunneling of atoms between adjacent sites lowers this energy barrier and hence facilitates the transition. Within our simplified description, we are thus able to augment the phase diagram of the model with information concerning the height of the barrier separating the metastable minima from the global minimum in each phase, which is an essential aspect for the understanding of the reconfiguration dynamics induced by a quench across a quantum critical point.Fil: Wald, Sascha. Sissa - International School For Advanced Studies; Italia. Universitat Saarland; AlemaniaFil: Timpanaro, André M.. Universidade Federal Do Abc; BrasilFil: Cormick, Maria Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Landi, Gabriel T.. Universidade de Sao Paulo; Brasi