21,648 research outputs found
Local Manipulation of Nuclear Spin in a Semiconductor Quantum Well
The shaping of nuclear spin polarization profiles and the induction of
nuclear resonances are demonstrated within a parabolic quantum well using an
externally applied gate voltage. Voltage control of the electron and hole wave
functions results in nanometer-scale sheets of polarized nuclei positioned
along the growth direction of the well. RF voltages across the gates induce
resonant spin transitions of selected isotopes. This depolarizing effect
depends strongly on the separation of electrons and holes, suggesting that a
highly localized mechanism accounts for the observed behavior.Comment: 18 pages, 4 figure
Analytic structure of solutions to multiconfiguration equations
We study the regularity at the positions of the (fixed) nuclei of solutions
to (non-relativistic) multiconfiguration equations (including Hartree--Fock) of
Coulomb systems. We prove the following: Let {phi_1,...,phi_M} be any solution
to the rank--M multiconfiguration equations for a molecule with L fixed nuclei
at R_1,...,R_L in R^3. Then, for any j in {1,...,M} and k in {1,...,L}, there
exists a neighbourhood U_{j,k} in R^3 of R_k, and functions phi^{(1)}_{j,k},
phi^{(2)}_{j,k}, real analytic in U_{j,k}, such that phi_j(x) =
phi^{(1)}_{j,k}(x) + |x - R_k| phi^{(2)}_{j,k}(x), x in U_{j,k} A similar
result holds for the corresponding electron density. The proof uses the
Kustaanheimo--Stiefel transformation, as applied earlier by the authors to the
study of the eigenfunctions of the Schr"odinger operator of atoms and molecules
near two-particle coalescence points.Comment: 15 page
Dynamical Diffraction Theory for Wave Packet Propagation in Deformed Crystals
We develop a theory for the trajectory of an x ray in the presence of a
crystal deformation. A set of equations of motion for an x-ray wave packet
including the dynamical diffraction is derived, taking into account the Berry
phase as a correction to geometrical optics. The trajectory of the wave packet
has a shift of the center position due to a crystal deformation. Remarkably, in
the vicinity of the Bragg condition, the shift is enhanced by a factor (: frequency of an x ray, : gap frequency
induced by the Bragg reflection). Comparison with the conventional dynamical
diffraction theory is also made.Comment: 4 pages, 2 figures. Title change
Exact PT-Symmetry Is Equivalent to Hermiticity
We show that a quantum system possessing an exact antilinear symmetry, in
particular PT-symmetry, is equivalent to a quantum system having a Hermitian
Hamiltonian. We construct the unitary operator relating an arbitrary
non-Hermitian Hamiltonian with exact PT-symmetry to a Hermitian Hamiltonian. We
apply our general results to PT-symmetry in finite-dimensions and give the
explicit form of the above-mentioned unitary operator and Hermitian Hamiltonian
in two dimensions. Our findings lead to the conjecture that non-Hermitian
CPT-symmetric field theories are equivalent to certain nonlocal Hermitian field
theories.Comment: Few typos have been corrected and a reference update
The Interpretations For the Low and High Frequency QPO Correlations of X-ray Sources Among White Dwarfs, Neutron Stars and Black Holes
It is found that there exists an empirical linear relation between the high
frequency \nhigh and low frequency \nlow of quasi-periodic oscillations
(QPOs) for black hole candidate (BHC), neutron star (NS) and white dwarf (WD)
in the binary systems, which spans five orders of magnitude in frequency.
For the NS Z (Atoll) sources,
and are identified as the lower kHz QPO frequency
and horizontal branch oscillations (HBOs) \nh (broad noise components); for
the black hole candidates and low-luminosity neutron stars, they are the QPOs
and broad noise components at frequencies between 1 and 10 Hz; for WDs, they
are the ``dwarf nova oscillations'' (DNOs) and QPOs of cataclysmic variables
(CVs). To interpret this relation, our model ascribes to the
Alfv\'en wave oscillation frequency at a preferred radius and to
the same mechanism at another radius. Then, we can obtain \nlow = 0.08
\nhigh and the relation between the upper kHz QPO frequency \nt and HBO to
be \nh \simeq 56 ({\rm Hz}) (\nt/{\rm kHz})^{2}, which are in accordance with
the observed empirical relations. Furthermore, some implications of model are
discussed, including why QPO frequencies of white dwarfs and neutron stars span
five orders of magnitude in frequency. \\Comment: 11 pages, 1 figure, accepted by PAS
Quantitative conditions do not guarantee the validity of the adiabatic approximation
In this letter, we point out that the widely used quantitative conditions in
the adiabatic theorem are insufficient in that they do not guarantee the
validity of the adiabatic approximation. We also reexamine the inconsistency
issue raised by Marzlin and Sanders (Phys. Rev. Lett. 93, 160408, 2004) and
elucidate the underlying cause.Comment: corrected typos. Eq. (32) is corrected. No other change
Electron Addition Spectrum in the Supersymmetric t-J Model with Inverse-Square Interaction
The electron addition spectrum A^+(k,omega) is obtained analytically for the
one-dimensional (1D) supersymmetric t-J model with 1/r^2 interaction. The
result is obtained first for a small-sized system and its validity is checked
against the numerical calculation. Then the general expression is found which
is valid for arbitrary size of the system. The thermodynamic limit of
A^+(k,omega) has a simple analytic form with contributions from one spinon, one
holon and one antiholon all of which obey fractional statistics. The upper edge
of A^+(k,omega) in the (k,omega) plane includes a delta-function peak which
reduces to that of the single-electron band in the low-density limit.Comment: 5 pages, 1 figure, accepted for publication in Phys. Rev. Let
Jack polynomials with prescribed symmetry and hole propagator of spin Calogero-Sutherland model
We study the hole propagator of the Calogero-Sutherland model with SU(2)
internal symmetry. We obtain the exact expression for arbitrary non-negative
integer coupling parameter and prove the conjecture proposed by one of
the authors. Our method is based on the theory of the Jack polynomials with a
prescribed symmetry.Comment: 12 pages, REVTEX, 1 eps figur
On hybrid states of two and three level atoms
We calculate atom-photon resonances in the Wigner-Weisskopf model, admitting
two photons and choosing a particular coupling function. We also present a
rough description of the set of resonances in a model for a three-level atom
coupled to the photon field. We give a general picture of matter-field
resonances these results fit into.Comment: 33 pages, 12 figure
Spatial imaging of the spin Hall effect and current-induced polarization in two-dimensional electron gases
Spin-orbit coupling in semiconductors relates the spin of an electron to its
momentum and provides a pathway for electrically initializing and manipulating
electron spins for applications in spintronics and spin-based quantum
information processing. This coupling can be regulated with quantum confinement
in semiconductor heterostructures through band structure engineering. Here we
investigate the spin Hall effect and current-induced spin polarization in a
two-dimensional electron gas confined in (110) AlGaAs quantum wells using Kerr
rotation microscopy. In contrast to previous measurements, the spin Hall
profile exhibits complex structure, and the current-induced spin polarization
is out-of-plane. The experiments map the strong dependence of the
current-induced spin polarization to the crystal axis along which the electric
field is applied, reflecting the anisotropy of the spin-orbit interaction.
These results reveal opportunities for tuning a spin source using quantum
confinement and device engineering in non-magnetic materials.Comment: Accepted for publication (2005
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