133 research outputs found
Electron Clusters in Inert Gases
The paper addresses counterintuitive behavior of electrons injected into
dense cryogenic media with negative scattering length . Instead of
expected polaronic effect (formation of density enhancement clusters) which
should substantially reduce the electron mobility, an opposite picture is
observed: with increasing (the trend taking place for inert gases with
the growth of atomic number) and the medium density, the electrons remain
practically free. An explanation of this behaviour is provided based on
consistent accounting for the non-linearity of electron interaction with the
gaseous medium in the gas atom number density
On the Teleportation of Continuous Variable
The measurement procedures used in quantum teleportation are analyzed from
the viewpoint of the general theory of quantum-mechanical measurements. It is
shown that to find the teleported state one should only know the identity
resolution (positive operator-valued measure) generated by the corresponding
instrument (quantum operation describing the system state change caused by the
measurement) rather than the instrument itself. A quantum teleportation
protocol based on a measurement associated with a non-orthogonal identity
resolution is proposed for a system with non-degenerate continuous spectrum.Comment: 13 pages, no figures. To be published in JET
Relativistic quantum coin tossing
A relativistic quantum information exchange protocol is proposed allowing two
distant users to realize ``coin tossing'' procedure. The protocol is based on
the point that in relativistic quantum theory reliable distinguishing between
the two orthogonal states generally requires a finite time depending on the
structure of these states.Comment: 6 pages, no figure
Magnetoplasmon excitations in arrays of circular and noncircular quantum dots
We have investigated the magnetoplasmon excitations in arrays of circular and
noncircular quantum dots within the Thomas-Fermi-Dirac-von Weizs\"acker
approximation. Deviations from the ideal collective excitations of isolated
parabolically confined electrons arise from local perturbations of the
confining potential as well as interdot Coulomb interactions. The latter are
unimportant unless the interdot separations are of the order of the size of the
dots. Local perturbations such as radial anharmonicity and noncircular symmetry
lead to clear signatures of the violation of the generalized Kohn theorem. In
particular, the reduction of the local symmetry from SO(2) to results in
a resonant coupling of different modes and an observable anticrossing behaviour
in the power absorption spectrum. Our results are in good agreement with recent
far-infrared (FIR) transmission experiments.Comment: 25 pages, 6 figures, typeset in RevTe
Relativistic Restrictions on the Distinguishability of Orthogonal Quantum States
We analyze the restrictions on the distinguishability of quantum states
imposed by special relativity. An explicit expression relating the error
probability for distinguishing between two orthogonal single-photon states with
the time elapsed from the start of the measurement procedure until the
measurement result is obtained by the observer.Comment: 9 pages, 1 figure (misprints in formulas corrected
Transport properties of copper phthalocyanine based organic electronic devices
Ambipolar charge carrier transport in Copper phthalocyanine (CuPc) is studied
experimentally in field-effect transistors and metal-insulator-semiconductor
diodes at various temperatures. The electronic structure and the transport
properties of CuPc attached to leads are calculated using density functional
theory and scattering theory at the non-equilibrium Green's function level. We
discuss, in particular, the electronic structure of CuPc molecules attached to
gold chains in different geometries to mimic the different experimental setups.
The combined experimental and theoretical analysis explains the dependence of
the mobilityand the transmission coefficient on the charge carrier type
(electrons or holes) and on the contact geometry. We demonstrate the
correspondence between our experimental results on thick films and our
theoretical studies of single molecule contacts. Preliminary results for
fluorinated CuPc are discussed.Comment: 18 pages, 16 figures; to be published in Eur. Phys. J. Special Topic
Spontaneous Coherence and Collective Modes in Double-Layer Quantum Dot Systems
We study the ground state and the collective excitations of
parabolically-confined double-layer quantum dot systems in a strong magnetic
field. We identify parameter regimes where electrons form maximum density
droplet states, quantum-dot analogs of the incompressible states of the bulk
integer quantum Hall effect. In these regimes the Hartree-Fock approximation
and the time-dependent Hartree-Fock approximations can be used to describe the
ground state and collective excitations respectively. We comment on the
relationship between edge excitations of dots and edge magneto-plasmon
excitations of bulk double-layer systems.Comment: 20 pages (figures included) and also available at
http://fangio.magnet.fsu.edu/~jhu/Paper/qdot_cond.ps, replaced to fix figure
Green function techniques in the treatment of quantum transport at the molecular scale
The theoretical investigation of charge (and spin) transport at nanometer
length scales requires the use of advanced and powerful techniques able to deal
with the dynamical properties of the relevant physical systems, to explicitly
include out-of-equilibrium situations typical for electrical/heat transport as
well as to take into account interaction effects in a systematic way.
Equilibrium Green function techniques and their extension to non-equilibrium
situations via the Keldysh formalism build one of the pillars of current
state-of-the-art approaches to quantum transport which have been implemented in
both model Hamiltonian formulations and first-principle methodologies. We offer
a tutorial overview of the applications of Green functions to deal with some
fundamental aspects of charge transport at the nanoscale, mainly focusing on
applications to model Hamiltonian formulations.Comment: Tutorial review, LaTeX, 129 pages, 41 figures, 300 references,
submitted to Springer series "Lecture Notes in Physics
Gravitational Waves from Gravitational Collapse
Gravitational wave emission from the gravitational collapse of massive stars
has been studied for more than three decades. Current state of the art
numerical investigations of collapse include those that use progenitors with
realistic angular momentum profiles, properly treat microphysics issues,
account for general relativity, and examine non--axisymmetric effects in three
dimensions. Such simulations predict that gravitational waves from various
phenomena associated with gravitational collapse could be detectable with
advanced ground--based and future space--based interferometric observatories.Comment: 68 pages including 13 figures; revised version accepted for
publication in Living Reviews in Relativity (http://www.livingreviews.org
Orbital redistribution in molecular nanostructures mediated by metal-organic bonds
Dicyanovinyl-quinquethiophene (DCV5T-Me) is a prototype conjugated oligomer for highly efficient organic solar cells. This class of oligothiophenes are built up by an electron-rich donor (D) backbone and terminal electron-deficient acceptor (A) moieties. Here, we investigated its structural and electronic properties when it is adsorbed on a Au(111) surface using low temperature scanning tunneling microscopy/spectroscopy (STM/STS) and atomic force microscopy (AFM). We find that DCV5T-Me self-assembles in extended chains, stabilized by intercalated Au atoms. The effect of metal-ligand hybridization with Au adatoms causes an energetic downshift of the DCV5T-Me lowest unoccupied molecular orbital (LUMO) with respect to the uncoordinated molecules on the surface. The asymmetric coordination of a gold atom to only one molecular end group leads to an asymmetric localization of the LUMO and LUMO+1 states at opposite sides. Using model density functional theory (DFT) calculations, we explain such orbital reshaping as a consequence of linear combinations of the original LUMO and LUMO+1 orbitals, mixed by the attachment of a bridging Au adatom. Our study shows that the alignment of molecular orbitals and their distribution within individual molecules can be modified by contacting them to metal atoms in specific sites
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