29 research outputs found
Quantum theory of an atom laser originating from a Bose-Einstein condensate or a Fermi gas in the presence of gravity
We present a 3D quantum mechanical theory of radio-frequency outcoupled atom
lasers from trapped atomic gases in the presence of the gravitational force.
Predictions for the total outcoupling rate as a function of the radio-frequency
and for the beam wave function are given. We establish a sum rule for the
energy integrated outcoupling, which leads to a separate determination of the
coupling strength between the atoms and the radiation field.
For a non-interacting Bose-Einstein condensate analytic solutions are derived
which are subsequently extended to include the effects of atomic interactions.
The interactions enhance interference effects in the beam profile and modify
the outcoupling rate of the atom laser. We provide a complete quantum
mechanical solution which is in line with experimental findings and allows to
determine the validity of commonly used approximative methods.
We also extend the formalism to a fermionic atom laser and analyze the effect
of superfluidity on the outcoupling of atoms.Comment: 13 pages, 8 figures, slightly expanded versio
Tunnel electron-vibrational spectroscopy of adsorbed complexes on the surface of ultra-small metal nanoparticles
This work was supported by the Russian Foundation for Basic Research (the project no. 18-03-00453) and into frameworks of the state task for ICP RAS 0082-2018-0003 (the state registration number АААА-А18-118012390045-2)
Propagation of charged particle waves in a uniform magnetic field
This paper considers the probability density and current distributions
generated by a point-like, isotropic source of monoenergetic charges embedded
into a uniform magnetic field environment. Electron sources of this kind have
been realized in recent photodetachment microscopy experiments. Unlike the
total photocurrent cross section, which is largely understood, the spatial
profiles of charge and current emitted by the source display an unexpected
hierarchy of complex patterns, even though the distributions, apart from
scaling, depend only on a single physical parameter. We examine the electron
dynamics both by solving the quantum problem, i. e., finding the energy Green
function, and from a semiclassical perspective based on the simple cyclotron
orbits followed by the electron. Simulations suggest that the semiclassical
method, which involves here interference between an infinite set of paths,
faithfully reproduces the features observed in the quantum solution, even in
extreme circumstances, and lends itself to an interpretation of some (though
not all) of the rich structure exhibited in this simple problem.Comment: 39 pages, 16 figure
Theory of Vibrationally Inelastic Electron Transport through Molecular Bridges
Vibrationally inelastic electron transport through a molecular bridge that is
connected to two leads is investigated. The study is based on a generic model
of vibrational excitation in resonant transmission of electrons through a
molecular junction. Employing methods from electron-molecule scattering theory,
the transmittance through the molecular bridge can be evaluated numerically
exactly. The current through the junction is obtained approximately using a
Landauer-type formula. Considering different parameter regimes, which include
both the case of a molecular bridge that is weakly coupled to the leads,
resulting in narrow resonance structures, and the opposite case of a broad
resonance caused by strong interaction with the leads, we investigate the
characteristic effects of coherent and dissipative vibrational motion on the
electron transport. Furthermore, the validity of widely used approximations
such as the wide-band approximation and the restriction to elastic transport
mechanisms is investigated in some detail.Comment: Submited to PRB, revised version according to comments of referees
(minor text changes and new citations
Probe tunneling microscopy/spectroscopy of polyoxometallate molecules
Описан новый (бирезонансный) механизм формирования резонансных особенностей туннельных спектров полиоксометаллатов. Приведены результаты сверх высоковакуумных и безвакуумных экспериментов, демонстрирующие перспективность применения этих соединений для создания молекулярных диодов и отрицательных дифференциальных сопротивлений.A new (biresonant) mechanism for the formation of resonance features of tunnel spectra of polyoxometallates is described. The results are presented in excess of high-vacuum and vacuum-free experiments, demonstrating the promise of using these compounds to create molecular diodes and negative differential resistances
Ballistic matter waves with angular momentum: Exact solutions and applications
An alternative description of quantum scattering processes rests on
inhomogeneous terms amended to the Schroedinger equation. We detail the
structure of sources that give rise to multipole scattering waves of definite
angular momentum, and introduce pointlike multipole sources as their limiting
case. Partial wave theory is recovered for freely propagating particles. We
obtain novel results for ballistic scattering in an external uniform force
field, where we provide analytical solutions for both the scattering waves and
the integrated particle flux. Our theory directly applies to p-wave
photodetachment in an electric field. Furthermore, illustrating the effects of
extended sources, we predict some properties of vortex-bearing atom laser beams
outcoupled from a rotating Bose-Einstein condensate under the influence of
gravity.Comment: 42 pages, 8 figures, extended version including photodetachment and
semiclassical theor