Search results for "Diabatic"
showing 10 items of 303 documents
The generalized Kadanoff-Baym ansatz with initial correlations
2018
Within the non-equilibrium Green's function (NEGF) formalism, the Generalized Kadanoff-Baym Ansatz (GKBA) has stood out as a computationally cheap method to investigate the dynamics of interacting quantum systems driven out of equilibrium. Current implementations of the NEGF--GKBA, however, suffer from a drawback: real-time simulations require {\em noncorrelated} states as initial states. Consequently, initial correlations must be built up through an adiabatic switching of the interaction before turning on any external field, a procedure that can be numerically highly expensive. In this work, we extend the NEGF--GKBA to allow for {\em correlated} states as initial states. Our scheme makes i…
Twist angle determination in liquid crystal displays by location of local adiabatic points
1998
In this work we present a method for the determination of the twist angle of an arbitrary twisted nematic liquid crystal spatial light modulator. The method is based on the location of local adiabatic points, i.e., situations in which the liquid crystal SLM acts only as a rotation device. For these cases, the rotation induced on the polarization of the incident beam is equal to the twist angle. Consequently, the twist angle can be determined with high precision. We show that local adiabatic regime may be achieved in two ways, either by changing the incident beam wavelength, or by applying a voltage to the electrodes of the display. However, the simple model that describes the SLM in the off…
Butterfly hysteresis curves generated by adiabatic Landau-Zener transitions
2006
Butterfly hysteresis curves observed in dynamical magnetization measurements on systems of low-spin magnetic molecules such as ${\mathrm{V}}_{15}$ can be explained by the interplay of adiabatic Landau-Zener transitions and relaxation. We investigate the magnetization dynamics analytically in the basis of the adiabatic energy levels of the spin $1∕2$, to a qualitative accordance with experimental observations. In particular, reversible behavior is found near zero field, the corresponding susceptibility being bounded by the equilibrium and adiabatic susceptibilities.
Motor strategies and adiabatic invariants: The case of rhythmic motion in parabolic flights
2021
The role of gravity in human motor control is at the same time obvious and difficult to isolate. It can be assessed by performing experiments in variable gravity. We propose that adiabatic invariant theory may be used to reveal nearly-conserved quantities in human voluntary rhythmic motion, an individual being seen as a complex time-dependent dynamical system with bounded motion in phase-space. We study an explicit realization of our proposal: An experiment in which we asked participants to perform $\infty-$ shaped motion of their right arm during a parabolic flight, either at self-selected pace or at a metronome's given pace. Gravity varied between $0$ and $1.8$ $g$ during a parabola. We c…
A Coherent Master Equation for active mode locking in lasers
2015
We present the derivation of a new master equation for active mode locking in lasers that fully takes into account the coherent effects of the light matter interaction through a peculiar adiabatic elimination technique. The coherent effects included in our model could be relevant to describe properly mode-locked semiconductor lasers where the standard Haus’ Master Equation predictions show some discrepancy with respect to the experimental results and can be included in the modelling of other mode locking techniques too.
Adiabatic eigenflows in a vertical porous channel
2014
AbstractThe existence of an infinite class of buoyant flows in a vertical porous channel with adiabatic and impermeable boundary walls, called adiabatic eigenflows, is discussed. A uniform heat source within the saturated medium is assumed, so that a stationary state is possible with a net vertical through-flow convecting away the excess heat. The simple isothermal flow with uniform velocity profile is a special adiabatic eigenflow if the power supplied by the heat source is zero. The linear stability analysis of the adiabatic eigenflows is carried out analytically. It is shown that these basic flows are unstable. The only exception, when the power supplied by the heat source is zero, is th…
Many-body quantum dynamics by adiabatic path-integral molecular dynamics: Disordered Frenkel Kontorova models
2005
The spectral density of quantum mechanical Frenkel Kontorova chains moving in disordered, external potentials is investigated by means of path-integral molecular dynamics. If the second moment of the embedding potential is well defined (roughness exponent ), there is one regime in which the chain is pinned (large masses of chain particles) and one in which it is unpinned (small ). If the embedding potential can be classified as a random walk on large length scales ( ), then the chain is always pinned irrespective of the value of . For , two phonon-like branches appear in the spectra.
Adiabatic charge pumping in carbon nanotube quantum dots.
2008
We investigate charge pumping in carbon nanotube quantum dots driven by the electric field of a surface acoustic wave. We find that, at small driving amplitudes, the pumped current reverses polarity as the conductance is tuned through a Coulomb blockade peak using a gate electrode. We study the behavior as a function of wave amplitude, frequency, and direction and develop a model in which our results can be understood as resulting from adiabatic charge redistribution between the leads and quantum dots on the nanotube.
Non-adiabatic manipulation of slow-light solitons
2005
We provide an exact analytic description of decelerating, stopping and reaccelerating optical solitons in atomic media in the non-adiabatic regime. Dynamical control over slow-light pulses is realized via a nonlinear interplay between the solitons and the controlling field generated by an auxiliary laser. This leads to recovery of optical information. We discuss physically interesting features of our solution, which are in good agreement with recent experiments.
Efficient adiabatic tracking of driven quantum nonlinear systems
2013
We derive a technique of robust and efficient adiabatic passage for a driven nonlinear quantum system, describing the transfer to a molecular Bose-Einstein condensate from an atomic one by external fields. The pulse ingredients are obtained by tracking the dynamics derived from a Hamiltonian formulation, in the adiabatic limit. This leads to a nonsymmetric and nonmonotonic chirp. The efficiency of the method is demonstrated in terms of classical phase space, more specifically with the underlying fixed points and separatrices. We also prove the crucial property that this nonlinear system does not have any solution leading exactly to a complete transfer. It can only be reached asymptotically …