An adaptive algorithm for n-body field expansions
Weinberg, Martin D.
1998-05-28
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34 records were found.
An idea for a nanodevice in which an arbitrary sequence of three basic
quantum single qubit gates - negation, Hadamard and phase shift - can be
performed on a single electron spin. The spin state is manipulated using the
spin-orbit coupling and the electron trajectory is controlled by the electron
wave function self-focusing mechanism due to the electron interaction with the
charge induced on metal gates. We present results of simulations based on
iterative solution of the time dependent Schr\"odinger equation in which the
subsequent operations on the electron spin can be followed and controlled.
Description of the moving electron wave packet requires evaluation of the
electric field within the entire nanodevice in each time step.
We study the artificial molecular states formed in laterally coupled double
semiconductor nanorings by systems containing one, two and three electrons. An
interplay of the interring tunneling and the electron-electron interaction is
described and its consequences for the magnetization and charging properties of
the system are determined. It is shown that both the magnetic dipole moment
generated by the double ring structure and the chemical potential of the system
as function of the external magnetic field strongly depend on the number of
electrons and the interring barrier thickness. Both the magnetization and
chemical potentials exhibit cusps at the magnetic fields inducing ground-state
parity and / or spin transformations. The symmetry transformations are
discussed for various tunnel coupling strengths: from rings coupled only
ele...
Pinning of magnetic-field induced Wigner molecules (WMs) confined in
parabolic two-dimensional quantum dots by a charged defect is studied by an
exact diagonalization approach. We found a re-entrant pinning of the WMs as
function of the magnetic field, a magnetic field induced re-orientation of the
WMs and a qualitatively different pinning behaviour in the presence of a
positive and negative Coulomb impurity.
We perform a systematic exact diagonalization study of spin-orbit coupling
effects for stationary few-electron states confined in quasi two-dimensional
double quantum dots. We describe the spin-orbit-interaction induced coupling
between bonding and antibonding orbitals and its consequences for
magneto-optical absorption spectrum. The spin-orbit coupling for odd electron
numbers (one, three) %only weakly perturbs the ground-state wave functions.
%Nevertheless, %the spin-orbit interaction opens avoided crossings between low
energy excited levels of opposite spin orientation and opposite spatial parity.
For two-electrons the spin-orbit coupling allows for low-energy optical
transitions that are otherwise forbidden by spin and parity selection rules. We
demonstrate that the energies of optical transitions can be significantly
increased b...
We study stationary electron flow through a three-terminal quantum ring and
describe effects due to deflection of electron trajectories by classical
magnetic forces. We demonstrate that generally at high magnetic field ($B$) the
current is guided by magnetic forces to follow a classical path which for $B>0$
leads via the left arm of the ring to the left output terminal. The transport
to the left output terminal is blocked for narrow windows of magnetic field for
which the interference within the ring leads to formation of wave functions
that are only weakly coupled to the output channel wave functions. These
interference conditions are accompanied by injection of the current to the
right arm of the ring and by appearance of sharp peaks of the transfer
probability to the right output terminal. We find that these peaks at high
magnetic...
We perform time-dependent simulations of spin exchange for an electron pair
in laterally coupled quantum dots. The calculation is based on configuration
interaction scheme accounting for spin-orbit (SO) coupling and
electron-electron interaction in a numerically exact way. Noninteracting
electrons exchange orientations of their spins in a manner that can be
understood by interdot tunneling associated with spin precession in an
effective SO magnetic field that results in anisotropy of the spin swap. The
Coulomb interaction blocks the electron transfer between the dots but the spin
transfer and spin precession due to SO coupling is still observed. The
electron-electron interaction additionally induces an appearance of spin
components in the direction of the effective SO magnetic field which are
opposite in both dots. Simulations indica...
We study avoided crossings opened by spin-orbit interaction in the energy
spectra of one- and two-electron anisotropic quantum dots in perpendicular
magnetic field. We find that for simultaneously present Rashba and Dresselhaus
interactions the width of avoided crossings and the effective $g$ factor depend
on the dot orientation within (001) crystal plane. The extreme values of these
quantities are obtained for [110] and [1$\bar{1}$0] orientations of the dot.
The width of singlet-triplet avoided crossing changes between these two
orientations by as much as two orders of magnitude. The discussed modulation
results from orientation-dependent strength of the Zeeman interaction which
tends to polarize the spins in the direction of the external magnetic field and
thus remove the spin-orbit coupling effects.
