Francisco de los Santos

Identifying Wave-Packet Fractional Revivals by Means of Information Entropy

Wave-packet fractional revivals is a relevant feature in the long time-scale evolution of a wide range of physical systems, including atoms, molecules, and nonlinear systems. We show that the sum of information entropies in both position and momentum conjugate spaces is an indicator of fractional revivals by analyzing three different model systems: (i) the infinite square well, (ii) a particle bouncing vertically against a wall in a gravitational field, and (iii) the vibrational dynamics of hydrogen iodide molecules. This description in terms of information entropies complements the usual one in terms of the autocorrelation function.

Understanding Diffusion and Density Anomaly in a Coarse-Grained Model for Water Confined between Hydrophobic Walls

We study, by Monte Carlo simulations, a coarse-grained model of a water monolayer between hydrophobic walls at partial hydration, with a wall-to-wall distance of about 0.5 nm. We analyze how the diffusion constant parallel to the walls, D(∥), changes and correlates to the phase diagram of the system. We find a locus of D(∥) maxima and a locus of D(∥) minima along isotherms, with lines of constant D(∥) resembling the melting line of bulk water. The two loci of D(∥) extrema envelope the line of temperatures of density maxima at constant P. We show how these loci are related to the anomalous volume behavior due to the hydrogen bonds. At much lower T, confined water becomes subdiffusive, and we discuss how this behavior is a consequence of the increased correlations among water molecules when the hydrogen bond network develops. Within the subdiffusive region, although translations are largely hampered, we observe that the hydrogen bond network can equilibrate, and its rearrangement is responsible for the appearance of density minima along isobars. We clarify that the minima are not necessarily related to the saturation of the hydrogen bond network.

Dynamically slow processes in supercooled water confined between hydrophobic plates

We study the dynamics of water confined between hydrophobic flat surfaces at low temperature. At different pressures, we observe different behaviors that we understand in terms of the hydrogen bond dynamics. At high pressure, the formation of the open structure of the hydrogen bond network is inhibited and the surfaces can be rapidly dried (dewetted) by formation of a large cavity with decreasing temperature. At lower pressure we observe strong non-exponential behavior of the correlation function, but with no strong increase of the correlation time. This behavior can be associated, on the one hand, to the rapid ordering of the hydrogen bonds that generates heterogeneities and, on the other hand, to the lack of a single timescale as a consequence of the cooperativity in the vicinity of the liquid-liquid critical point that characterizes the phase diagram at low temperature of the water model considered here. At very low pressures, the gradual formation of the hydrogen bond network is responsible for the large increase of the correlation time and, eventually, the dynamical arrest of the system, with a strikingly different dewetting process, characterized by the formation of many small cavities.

Application of new Rényi uncertainty relations to wave packet revivals

Wave packet revivals and fractional revivals are studied by means of newly derived uncertainty relations that involve Renyi entropies and position and momentum dispersions.

Influence of intramolecular couplings in a model for hydrogen‐bonded liquids

A brief review of recent work on the unique and unusual properties of water is given through results obtained from a simple cell model that reproduces qualitatively the behavior observed in experiments and molecular dynamics simulations. The attention is focused on results that help establish which theoretic scenario better describes the phase diagram of water.

Critical wetting of a class of nonequilibrium interfaces: a mean-field picture.

A self-consistent mean-field method is used to study critical wetting transitions under nonequilibrium conditions by analyzing Kardar-Parisi-Zhang (KPZ) interfaces in the presence of a bounding substrate. In the case of positive KPZ nonlinearity a single (Gaussian) regime is found. On the contrary, interfaces corresponding to negative nonlinearities lead to three different regimes of critical behavior for the surface order parameter: (i) a trivial Gaussian regime, (ii) a weak-fluctuation regime with a trivially located critical point and nontrivial exponents, and (iii) a highly nontrivial strong-fluctuation regime, for which we provide a full solution by finding the zeros of parabolic-cylinder functions. These analytical results are also verified by solving numerically the self-consistent equation in each case. Analogies with and differences from equilibrium critical wetting as well as nonequilibrium complete wetting are also discussed.

Critical wetting of a class of nonequilibrium interfaces : A computer simulation study

Critical wetting transitions under nonequilibrium conditions are studied numerically and analytically by means of an interface-displacement model defined by a Kardar-Parisi-Zhang equation, plus some extra terms representing a limiting, short-ranged attractive wall. Its critical behavior is characterized in detail by providing a set of exponents for both the average height and the surface order-parameter in one dimension. The emerging picture is qualitatively and quantitatively different from recently reported mean-field predictions for the same problem. Evidence is shown that the presence of the attractive wall induces an anomalous scaling of the interface local slopes.

Fisher information, nonclassicality and quantum revivals

We show the usefulness of the Fisher-Shannon information product in the study of the sequence of collapses and revivals that take place along the time evolution of quantum wavepackets. This fact is illustrated in two models, the quantum bouncer and a graphene quantum ring.Abstract Wave packet revivals and fractional revivals are studied by means of a measure of nonclassicality based on the Fisher information. In particular, we show that the spreading and the regeneration of initially Gaussian wave packets in a quantum bouncer and in the infinite square-well correspond, respectively, to high and low nonclassicality values. This result is in accordance with the physical expectations that at a quantum revival wave packets almost recover their initial shape and the classical motion revives temporarily afterward.

Quantum revivals and Zitterwebegung in monolayer graphene

We have studied the dynamics of electron currents in graphene subject to a magnetic field. Several types of periodicity must be distinguished if the wave packets representing the electrons are sufficiently localized around some large enough central quantum number n0. In this case, currents initially evolve quasiclassically and oscillate with a period TCl, but at later times the wave packet eventually spreads, leading to the collapse of the classical oscillations. At times that are multiple of TR, or rational fractions of TR, the wave packet (almost) regains its initial form, and the electron current its initial amplitude. For this to occur, the presence of a quantizing magnetic field is necessary, for if B = 0 the spectrum is continuous which rules out the possibility of revivals. Associated with the revival of the wave packet the quasiclassical oscillatory motion of the currents resumes. Additionally, when both positive and negative Landau levels are populated, permanent ZB oscillations are observed, in ...