128 research outputs found
Magnetic noise spectrum measurement by an atom laser in gravity
Bose-Einstein condensates of ultracold atoms can be used to sense
fluctuations of the magnetic field by means of transitions into untrapped
hyperfine states. It has been shown recently that counting the outcoupled atoms
can yield the power spectrum of the magnetic noise. We calculate the spectral
resolution function which characterizes the condensate as a noise measurement
device in this scheme. We use the description of the radio-frequency
outcoupling scheme of an atom laser which takes into account the gravitational
acceleration. Employing both an intuitive and the exact three-dimensional and
fully quantum mechanical approach we derive the position-dependent spectral
resolution function for condensates of different size and shape
Parametric amplification of the mechanical vibrations of a suspended nanowire by magnetic coupling to a Bose-Einstein condensate
We consider the possibility of parametric amplification of a mechanical
vibration mode of a nanowire due to its interaction with a Bose-Einstein
condensate (BEC) of ultracold atoms. The magneto-mechanical coupling is
mediated by the vibrationally modulated magnetic field around the
current-carrying nanowire, which can induce atomic transitions between
different hyperfine sublevels. We theoretically analyze the limitations arising
from the fact that the spin inverted atomic medium which feeds the mechanical
oscillation has a finite bandwidth in the range of the chemical potential of
the condensate
Magnetoconductance properties of rectangular arrays of spintronic quantum rings
Electron transport through multi-terminal rectangular arrays of quantum rings
is studied in the presence of Rashba-type spin-orbit interaction (SOI) and of a
perpendicular magnetic field. Using the analytic expressions for the
transmission and reflection coefficients for single rings we obtain the
conductance through such arrays as a function of the SOI strength, the magnetic
flux, and of the wave vector of the incident electron. Due to destructive
or constructive spin interferences caused by the SOI, the array can be totally
opaque for certain ranges of , while there are parameter values where it is
completely transparent. Spin resolved transmission probabilities show
nontrivial spin transformations at the outputs of the arrays. When point-like
random scattering centers are placed between the rings, the Aharonov-Bohm peaks
split, and an oscillatory behavior of the conductance emerges as a function of
the SOI strength.Comment: 10 pages, 10 figures, submitted to PR
Hataratlepes es Inkluzio – Tanarok Tanulasanak Tamogatasa
A tanulmány egy olyan nemzetközi projekt eredményeit és fejlesztéseit összegzi, melynek célja az inkluzív oktatás támogatása érdekében gyakorló tanárok és tanárjelöltek tanulását segítő anyagok kidolgozása és fejlesztése. A projekt abból az elméleti alapvetésből indul ki, hogy a komplex iskolai problémák kezeléséhez a szereplők közti együttműködés szükséges, ehhez készít támogató anyagokat. Jelen tanulmány a projektben zajló fejlesztés elméleti kereteinek rövid összegzését követően a projektben kifejlesztett eszközöket mutatja be, majd ismerteti egy pilot képzés fejlesztésének vizsgálatát. A pilot fejlesztése a kutatás alapú tervezés megközelítésre épül, ennek vizsgálati elemeit és eredményeit ismertetjük a kutatási részben. Az eredmények azt mutatják, hogy a tananyagok segítik a közös probléma-feldolgozást, az eszközök különösen sikeresnek mutatkoztak a pedagógusok többszempontú problémamegoldásának ösztönzésében
Spin Density Distribution in a Nitroxide Biradical Containing 13C-Enriched Acetylene Groups in the Bridge: DFT Calculations and EPR Investigation
Abstract A specially synthesized nitroxide biradical R6-13C:C-p-C6H4–C:13CR6,B3, where R6 = 1-oxyl-2,2,6,6-tetramethyl-1,2,3,6-tetrahydropyridine nitroxide,
has been studied by electron paramagnetic resonance spectroscopy, and electron-nuclear double resonance (ENDOR). Spin density distribution and hyperfine
splitting (hfs) constant on 13C atoms calculations for biradical B3 were carried out using B3LYP and PBE0 functionals and several different basis sets including N07 family and were compared with the experimental value of the hfs constant on 13C atoms, measured from ENDOR spectra of B3. The mechanism of the intramolecular
electron spin exchange in B3 biradical is discussed
Networks of quantum nanorings: programmable spintronic devices
An array of quantum rings with local (ring by ring) modulation of the spin
orbit interaction (SOI) can lead to novel effects in spin state transformation
of electrons. It is shown that already small (3x3, 5x5) networks are remarkably
versatile from this point of view: Working in a given network geometry, the
input current can be directed to any of the output ports, simply by changing
the SOI strengths by external gate voltages. Additionally, the same network
with different SOI strengths can be completely analogous to the Stern-Gerlach
device, exhibiting spatial-spin entanglement.Comment: 4 pages, 3 figures, accepted by Nano Letter
Borromean Binding of Three or Four Bosons
We estimate the ratio of the critical coupling constants
and which are required to achieve binding of 2 or 3 bosons,
respectively, with a short-range interaction, and examine how this ratio
depends on the shape of the potential. Simple monotonous potentials give
. A wide repulsive core pushes this ratio close to R=1. On the
other hand, for an attractive well protected by an external repulsive barrier,
the ratio approaches the rigorous lower bound . We also present results
for N=4 bosons, sketch the extension to , and discuss various
consequences.Comment: 12 pages, RevTeX, 5 Figures in tex include
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