The phenomenological Landau theory of the spin precession has been used to reproduce the out-of-equilibrium properties of many magnetic systems. However, such an approach suffers from some serious ...limitations. The main reason is that the spin and the angular momentum of the atoms are described by the classical theory of the angular momentum. We derive a discrete model that extends the Landau theory to the quantum mechanical framework. Our approach is based on the application of the quantification procedure to the classical Hamiltonian of an array of interacting spins. The connection with the classical dynamics is discussed.
Debris flows constitute a severe natural hazard in Alpine regions. Studies are performed to understand the event predictability and to identify early warning systems and procedures. These are based ...both on sensors deployed along the channels or on the amplitude of seismic and infrasound waves radiated by the flow and recorded far away. Despite being very promising, infrasound cannot be used to infer the source characteristics due to the lack of a physical model of the infrasound energy radiated by debris flows. Here the simulation of water flow along a simple channel is presented, experiencing the fall from a dam, performed within the open source simulation code OpenFOAM. The pressure perturbation within the atmosphere produced by the flow is extracted and the infrasound signature of the events as a function of the flow characteristics is defined. Numerical results suggest that infrasound is radiated immediately downstream of the dam with amplitude and period that scale with dam height and water level. Modeled infrasound waveform is interpreted as being produced mostly by waves at the water free surface developing downstream of the dam. Despite the effect of sediments is not considered in this first study and will be implemented in future investigations, numerical results obtained with this simple model are in general agreement with experimental results obtained from array analysis of infrasound data recorded at Illgraben, Switzerland. Results highlight how numerical modeling can provide critical information to define a source mechanism of infrasound energy radiation by debris-flow, that is required also to improve early warning systems.
We investigate the entanglement in a two-particle system with continuous degree of freedom constituted by trapped neutral atoms interacting via tunable dipole-dipole interaction. We describe the ...system in the quantum Wigner phase space representation. The atom entanglement is measured in terms of violation of the non separability condition or of some Bell inequalities. By an optimal control procedure, we design the control parameters that steer the system toward a maximally entangled state. We estimate the robustness of the control by considering the presence of an external source of noise weakly interacting with the atoms.
•Optimal Control of an atomic gas in dipolar interaction.•Dynamical control of entanglement in interacting particles.•Optimal control applied to the Wigner phase space formalism.•Bell's inequalities and separability condition in continuous variable systems: phase space description.
In this paper, we discuss the connection between two alternative descriptions of the quantum motion proposed by Wigner in 1932 and by Bohm in 1952. Such formalism provides different representations ...of the quantum dynamics. The Wigner description is based on the definition of a non positive quasi-distribution function in the quantum phase space and the Bohm formalism on the introduction of the pilot wave field associated to the particle motion along trajectories. We discuss the representation of the Bohm dynamics in the phase space in terms of a suitable Wigner measure. We propose an extension of the Wigner transformation and we derive a family of models where the quantum dynamics is described by equivalent mathematical formulations. Similarly to the classical limit, we show the asymptotic convergence in distributional sense of the extended Wigner distribution to a measure. We prove that such a limit is the solution of a classical Liouville equation containing as a quantum correction the Bohm potential.
•Quantum properties of atoms impact the electronic structure of nanomaterials.•Alternative interpretations of quantum mechanics have found renewed interest.•Mathematical link between the Wigner phase space motion and the Bohm dynamics.•Classical-to-quantum transition understood in terms of motion in phase space.
A mathematical model for the quantum transport of a two-band semiconductor that includes the self-consistent electrostatic potential is analyzed. Corrections beyond the usual effective mass ...approximation are considered. Transparent boundary conditions are derived for the multiband envelope Schrödinger model. The existence of a solution of the nonlinear system is proved by using an asymptotic procedure. Some numerical examples are included. They illustrate the behavior of the scattering and the resonant states.
We study the effect of electron spill-out and of nonlocality on the propagation of light inside a gap between two semi-infinite metallic regions. We compare the predictions of a local response model ...taking into account only the spill-out, to the predictions of a quantum hydrodynamic model able to take both phenomena into account. We show that only the latter is able to correctly retrieve the correct limit when the gap closes, while the local model suffers from undesirable features (divergence of the fields, overestimation of the losses). Finally, we show that, to a certain extent, the correct results can be retrieved using a simple local approach without spill-out or a conventional Thomas-Fermi approximation, but considering an effective gap width.
We investigate the particle dynamics in a two-dimensional structure containing two different populations of particles. We consider the semiclassical high temperature limit of the particle gas. The ...particle motion is described at the hydrodynamic level. We show the existence of a regime, denoted as collimated beam limit, where the problem of the closure of the hydrodynamic moments hierarchy simplifies considerably. Some numerical experiments are presented in which our model is applied to the numerical simulation of a nanometric device based on a graphene sheet.
We investigate the ultrafast dynamics of the atomic angular momentum in ferrimagnets irradiated by laser pulses. Our study is based on a quantum atomistic approach and the particle dynamics is ...performed using a Monte Carlo technique. We focus on microscopic mechanisms that lead to the dissipation of the total angular momentum in a rare earth–transition metal (RE-TM) alloy in which the two sublattices have opposite spin orientation. We describe the coherent transfer of atomic angular momentum between the spin and the orbital momentum. The orbital momentum quenching induced by the lattice field and the Elliott-Yafet collision mechanism are also included. The simulations show that the observed ultrafast magnetization quenching may be explained at a microscopical level by the combined effects of the coherent spin transfer between the RE and the TM sublattices along with the quenching of the localized orbital angular momentum induced by the lattice field.
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