Search results for "Adiabatic process"
showing 10 items of 237 documents
Tunneling-charging Hamiltonian of a Cooper-pair pump
2001
General properties of the tunneling-charging Hamiltonian of a Cooper pair pump are examined with emphasis on the symmetries of the model. An efficient block-diagonalization scheme and a compatible Fourier expansion of the eigenstates is constructed and applied in order to gather information on important observables. Systematics of the adiabatic pumping with respect to all of the model parameters are obtained and the link to the geometrical Berry's phase is identified.
Preparation of coherent superposition in a three-state system by adiabatic passage
2004
We examine the topology of eigenenergy surfaces associated to a three-state system driven by two quasi-resonant fields. We deduce mechanisms that allow us to generate various coherent superposition of two states using an additional field, far off resonances. We report the numerical validations in mercury atoms as a model system, creating the coherent superpositions of two excited states and of two states coupled by a Raman process.
Rotational Three-Body Resonances: A New Adiabatic Approach
2001
In the standard adiabatic approach the motion of the fast, light particle (electron) is treated so as to produce an effective potential that governs the motion of the heavy particles (nuclei). The rotational degrees of freedom are then taken into account by adding the centrifugal J(J + 1)-term to the channel potentials and introducing rotational (Coriolis) couplings into conventional close-coupling calculations. Of course, a perturbative treatment of the rotational motion is justified only provided the rotational energy is sufficiently small. If, however, the rotation is as energetic as the motion of the fast particle, both motions should be treated on the same footing in order to produce s…
Multidimensional Skyrme-density-functional Study of the Spontaneous Fission of 238U
2015
We determined the spontaneous fission lifetime of 238U by a minimization of the action integral in a three-dimensional space of collective variables. Apart from the mass-distribution multipole moments Q20 (elongation) and Q30 (left–right asymmetry), we also considered the pairing- fluctuation parameter λ2 as a collective coordinate. The collective potential was obtained self-consistently using the Skyrme energy density functional SkM∗ . The inertia tensor was obtained within the nonperturbative cranking approximation to the adiabatic time-dependent Hartree–Fock– Bogoliubov approach. The pairing-fluctuation parameter λ2 allowed us to control the pairing gap along the fission path, which sign…
Time-dependent density-functional theory for strongly interacting electrons
2017
We consider an analytically solvable model of two interacting electrons that allows for the calculation of the exact exchange-correlation kernel of time-dependent density functional theory. This kernel, as well as the corresponding density response function, is studied in the limit of large repulsive interactions between the electrons and we give analytical results for these quantities as an asymptotic expansion in powers of the square root of the interaction strength. We find that in the strong interaction limit the three leading terms in the expansion of the kernel act instantaneously while memory terms only appear in the next orders. We further derive an alternative expansion for the ker…
Detuning-induced robustness of a three-state Landau-Zener model against dissipation
2019
A three-state system subjected to a time-dependent Hamiltonian whose bare energies undergo one or more crossings, depending on the relevant parameters, is considered, also taking into account the role of dissipation in the adiabatic following of the Hamiltonian eigenstates. Depending on the fact that the bare energies are equidistant or not, the relevant population transfer turns out to be very sensitive to the environmental interaction or relatively robust. The physical mechanisms on the basis of this behavior are discussed in detail.
Characterization of a Modified Expansion Condensation Particle Counter for Detection of Nanometer-Sized Particles
2009
A newly developed condensation particle counter provides measurements of aerosol particle number densities for size diameters as low as 3 nm. This Expansion Condensation Particle Counter (ECPC) operates based on fast adiabatic expansion with specialized detection and evaluation of the temporal development of light scattered by the ensemble of growing droplets. In its new configuration the ECPC has been modified such that a previously needed calibration factor became obsolete. In this article the new design is described which now includes a fast pressure sensor for monitoring the pressure drop inside the measurement chamber. Extensive laboratory experiments for characterizing the ECPC are de…
New approach to describe two coupled spins in a variable magnetic field
2021
We propose a method to describe the evolution of two spins coupled by hyperfine i nteraction in an external time- dependent magnetic field. We apply the approach to the case of hyperfine interaction with axial symmetry, which can be solved exactly in a constant, appropriately oriented magnetic field. In order to t reat t he n onstationary d ynamical p roblem, we modify the time-dependent Schrödinger equation through a change of representation that, by exploiting an instantaneous (adiabatic) basis makes the time-dependent Hamiltonian diagonal at any time instant. The solution of the transformed time-dependent Schrödinger FRVBUJPO in the form of chronologically ordered exponents with transpar…
Results from pQCD for A+A collisions at RHIC & LHC energies
2000
This talk will discuss how to compute initial quantites in heavy ion collisions at RHIC (200 AGeV) and at LHC (5500 AGeV) using perturbative QCD (pQCD) by including the next-to-leading order (NLO) corrections and a dynamical determination of the dominant physical scale. The initial numbers are converted into final ones by assuming kinetic thermalization and adiabatic expansion.
Effects of an environment on a cavity-quantum-electrodynamics system controlled by bichromatic adiabatic passage
2012
International audience; We present a theoretical investigation of a cavity-QED system controlled by bichromatic adiabatic passage in a dissipative environment. We analyze the production of a controlled Fock state in the cavity by a traveling atom simultaneously coupled by a laser field, and the leakage of the corresponding photons from the cavity.