Breakdown of the Landauer bound for information erasure in the quantum regime.

A known aspect of the Clausius inequality is that an equilibrium system subjected to a squeezing dS < 0 of its entropy must release at least an amount the absolute value of dQ = T times the absolute value of dS of heat. This serves as a basis for the Landauer principle, which puts a lower bound T ln 2 for the heat generated by erasure of one bit of information. Here we show that in the world of quantum entanglement this law is broken. A quantum Brownian particle interacting with its thermal bath can either generate less heat or even absorb heat during an analogous squeezing process, due to entanglement with the bath. The effect exists even for weak but fixed coupling with the bath, provided that temperature is low enough. This invalidates the Landauer bound in the quantum regime, and suggests that quantum carriers of information can be more efficient than assumed so far.

Inherent structures in models for fragile and strong glass.

An analysis of the dynamics is performed of exactly solvable models for fragile and strong glasses, exploiting the partitioning of the free-energy landscape in inherent structures. The results are compared with the exact solution of the dynamics, by employing the formulation of an effective temperature used in literature. Also, a statistical mechanics formulation is introduced, based upon general statistical considerations, which performs better. Though the considered models are conceptually simple, there is no limit in which the dynamics may be exactly described by a symbolic dynamics of the system moving through consistently weighted inherent structures.

Random walks of cytoskeletal motors in open and closed compartments.

Random walks of molecular motors, which bind to and unbind from cytoskeletal filaments, are studied theoretically. The bound and unbound motors undergo directed and nondirected motion, respectively. Motors in open compartments exhibit anomalous drift velocities. Motors in closed compartments generate stationary nonequilibrium states with spatially varying densities of the motor concentrations and currents. "Traffic jams" on the filaments lead to a maximum of the motor current at an optimal motor concentration. Quantitative estimates based on experimental data for bound motors indicate that these transport phenomena are accessible to experiments.

Effective temperatures in an exactly solvable model for a fragile glass.

A model glass with facilitated dynamics is considered with one type of fast process (beta type) and one type of slow process (alpha type). On time scales where the fast processes are in equilibrium, the slow ones have a dynamics that resembles that of facilitated spin models. The main features are the occurrence of a Kauzmann transition, a Vogel-Fulcher-Tammann-Hesse behavior for the relaxation time, an Adam-Gibbs relation between relaxation time and configurational entropy, and an aging regime. The model is such that its statics is simple and its (Monte Carlo type) dynamics is exactly solvable. The dynamics has been studied both on the approach to the Kauzmann transition and below it. In certain parameter regimes it is so slow that a quasiequilibrium occurs at a time dependent effective temperature. Correlation and response functions are also computed, as well as the out of equilibrium fluctuation-dissipation relation, showing the uniqueness of the effective temperature, thus giving support to the rephrasing of the problem within the framework of out of equilibrium thermodynamics.

Competition between glassiness and order in a multispin glass.

A mean-field multispin interaction spin glass model is analyzed in the presence of a ferromagnetic coupling. The static and dynamical phase diagrams contain four phases (paramagnet, spin glass, ordinary ferromagnet, and glassy ferromagnet) and exhibit reentrant behavior. The glassy ferromagnet phase has anomalous dynamical properties. The results are consistent with a nonequilibrium thermodynamics that has been proposed for glasses.