1,251 research outputs found
Uniform Density Theorem for the Hubbard Model
A general class of hopping models on a finite bipartite lattice is
considered, including the Hubbard model and the Falicov-Kimball model. For the
half-filled band, the single-particle density matrix \uprho (x,y) in the
ground state and in the canonical and grand canonical ensembles is shown to be
constant on the diagonal , and to vanish if and if and
are on the same sublattice. For free electron hopping models, it is shown in
addition that there are no correlations between sites of the same sublattice in
any higher order density matrix. Physical implications are discussed.Comment: 15 pages, plaintex, EHLMLRJM-22/Feb/9
Quantum Computation and Spin Electronics
In this chapter we explore the connection between mesoscopic physics and
quantum computing. After giving a bibliography providing a general introduction
to the subject of quantum information processing, we review the various
approaches that are being considered for the experimental implementation of
quantum computing and quantum communication in atomic physics, quantum optics,
nuclear magnetic resonance, superconductivity, and, especially, normal-electron
solid state physics. We discuss five criteria for the realization of a quantum
computer and consider the implications that these criteria have for quantum
computation using the spin states of single-electron quantum dots. Finally, we
consider the transport of quantum information via the motion of individual
electrons in mesoscopic structures; specific transport and noise measurements
in coupled quantum dot geometries for detecting and characterizing
electron-state entanglement are analyzed.Comment: 28 pages RevTeX, 4 figures. To be published in "Quantum Mesoscopic
Phenomena and Mesoscopic Devices in Microelectronics," eds. I. O. Kulik and
R. Ellialtioglu (NATO Advanced Study Institute, Turkey, June 13-25, 1999
Exponential decay in a spin bath
We show that the coherence of an electron spin interacting with a bath of
nuclear spins can exhibit a well-defined purely exponential decay for special
(`narrowed') bath initial conditions in the presence of a strong applied
magnetic field. This is in contrast to the typical case, where spin-bath
dynamics have been investigated in the non-Markovian limit, giving
super-exponential or power-law decay of correlation functions. We calculate the
relevant decoherence time T_2 explicitly for free-induction decay and find a
simple expression with dependence on bath polarization, magnetic field, the
shape of the electron wave function, dimensionality, total nuclear spin I, and
isotopic concentration for experimentally relevant heteronuclear spin systems.Comment: 4+ pages, 3 figures; v2: 9 pages, 3 figures (added four appendices
with extensive technical details, version to appear in Phys. Rev. B
Discrete Fourier Transform in Nanostructures using Scattering
In this paper we show that the discrete Fourier transform can be performed by
scattering a coherent particle or laser beam off a two-dimensional potential
that has the shape of rings or peaks. After encoding the initial vector into
the two-dimensional potential, the Fourier-transformed vector can be read out
by detectors surrounding the potential. The wavelength of the laser beam
determines the necessary accuracy of the 2D potential, which makes our method
very fault-tolerant.Comment: 6 pages, 5 EPS figures, REVTe
Stability of Matter in Magnetic Fields
In the presence of arbitrarily large magnetic fields, matter composed of
electrons and nuclei was known to be unstable if or is too large.
Here we prove that matter {\it is stable\/} if and
.Comment: 10 pages, LaTe
Spin Hall effect due to intersubband-induced spin-orbit interaction in symmetric quantum wells
We investigate the intrinsic spin Hall effect in two-dimensional electron
gases in quantum wells with two subbands, where a new intersubband-induced
spin-orbit coupling is operative. The bulk spin Hall conductivity
is calculated in the ballistic limit within the standard Kubo
formalism in the presence of a magnetic field and is found to remain finite
in the B=0 limit, as long as only the lowest subband is occupied. Our
calculated exhibits a nonmonotonic behavior and can change its
sign as the Fermi energy (the carrier areal density ) is varied between
the subband edges. We determine the magnitude of for realistic
InSb quantum wells by performing a self-consistent calculation of the
intersubband-induced spin-orbit coupling.Comment: 7 pages, 3 figure
Suppression of tunneling by interference in half-integer--spin particles
Within a wide class of ferromagnetic and antiferromagnetic systems, quantum
tunneling of magnetization direction is spin-parity dependent: it vanishes for
magnetic particles with half-integer spin, but is allowed for integer spin. A
coherent-state path integral calculation shows that this topological effect
results from interference between tunneling paths.Comment: 14 pages (RevTeX), 2 postscript figures available upon reques
Anisotropic conductivity of disordered 2DEGs due to spin-orbit interactions
We show that the conductivity tensor of a disordered two-dimensional electron
gas becomes anisotropic in the presence of both Rashba and Dresselhaus
spin-orbit interactions (SOI). This anisotropy is a mesoscopic effect and
vanishes with vanishing charge dephasing time. Using a diagrammatic approach
including zero, one, and two-loop diagrams, we show that a consistent
calculation needs to go beyond a Boltzmann equation approach. In the absence of
charge dephasing and for zero frequency, a finite anisotropy \sigma_{xy}
e^2/lhpf arises even for infinitesimal SOI.Comment: 6+ page
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