127 research outputs found
Inverted Oscillator
The inverted harmonic oscillator problem is investigated quantum
mechanically. The exact wave function for the confined inverted oscillator is
obtained and it is shown that the associated energy eigenvalues are discrete
and it is given as a linear function of the quantum number .Comment: 4 page
Stability of an Exciton bound to an Ionized Donor in Quantum Dots
Total energy, binding energy, recombination rate (of the electron hole pair)
for an exciton (X) bound in a parabolic two dimensional quantum dot by a donor
impurity located on the z axis at a distance d from the dot plane, are
calculated by using the Hartree formalism with a recently developed numerical
method (PMM) for the solution of the Schroedinger equation. As our analysis
indicates there is a critical dot radius such that for radius less than the
critical radius the complex is unstable and with an increase of the impurity
distance this critical radius increases. Furthermore, there is a critical value
of the mass ratio such that for mass ratio less than the critical value the
complex is stable. The appearance of this stability condition depends both on
the impurity distance and the dot radius, in a way that with an increase of the
impurity distance we have an increase in the maximum dot radius where this
stability condition appears. For dot radii greater than this maximum dot radius
(for fixed impurity distance) the complex is always stable.Comment: 17 pages, 7 figures Applying a new numerical method which is based on
the adiabatic stability of quantum mechanics, we study the stability of an
exciton (X) bound in a parabolic two dimensional quantum dot by a donor
impurity located on the z axis at a distance d from the dot plan
On the construction of pseudo-hermitian quantum system with a pre-determined metric in the Hilbert space
A class of pseudo-hermitian quantum system with an explicit form of the
positive-definite metric in the Hilbert space is presented. The general method
involves a realization of the basic canonical commutation relations defining
the quantum system in terms of operators those are hermitian with respect to a
pre-determined positive definite metric in the Hilbert space. Appropriate
combinations of these operators result in a large number of pseudo-hermitian
quantum systems admitting entirely real spectra and unitary time evolution. The
examples considered include simple harmonic oscillators with complex angular
frequencies, Stark(Zeeman) effect with complex electric(magnetic) field,
non-hermitian general quadratic form of N boson(fermion) operators, symmetric
and asymmetric XXZ spin-chain in complex magnetic field, non-hermitian
Haldane-Shastry spin-chain and Lipkin-Meshkov-Glick model.Comment: 29 pages, revtex, minor changes, version to appear in Journal of
Physics A(v3
Quantum Tunneling in the Wigner Representation
Time dependence for barrier penetration is considered in the phase space. An
asymptotic phase-space propagator for nonrelativistic scattering on a one -
dimensional barrier is constructed. The propagator has a form universal for
various initial state preparations and local potential barriers. It is
manifestly causal and includes time-lag effects and quantum spreading. Specific
features of quantum dynamics which disappear in the standard semi-classical
approximation are revealed. The propagator may be applied to calculation of the
final momentum and coordinate distributions, for particles transmitted through
or reflected from the potential barrier, as well as for elucidating the
tunneling time problem.Comment: 18 pages, LATEX, no figure
Facile green synthesis of magnesium oxide nanoparticles using tea (Camellia sinensis) extract for efficient photocatalytic degradation of methylene blue dye
Herein, we report, for the first time, the synthesis, characterization, and the photocatalytic methyl blue dye degradation performance of magnesium oxide (MgO) nanoparticles (NPs) synthesized by a facile green approach using Camellia sinensis (tea leaves) extract as a reducing agent. The as-prepared materials were characterized by x-ray diffraction (XRD), which confirmed the large-scale synthesis of well crystalline cubic crystalline phase MgO NPs. Rietveld refinement analysis of the XRD pattern was done to determine the crystallographic parameters of the MgO NPs and to investigate lattice defects. Microstrain, lattice stress and energy density were calculated using Williamson-Hall analysis The synthesized nanoparticles exhibited over 97% photocatalytic degradation efficiency of methylene blue (MB) dye. Complementary density functional theory (DFT) calculations revealed the favorable formation of O
2
−
radicals on the MgO (001) surface as the drivers of the MB dye degradation
Binding energy of hydrogenic impurity states in an inverse parabolic quantum well under static external fields
68.65.Fg Quantum wells, 61.72.-y Defects and impurities in crystals; microstructure, 83.60.Np Effects of electric and magnetic fields,
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