17,475 research outputs found
The Nature and Location of Quantum Information
Quantum information is defined by applying the concepts of ordinary (Shannon)
information theory to a quantum sample space consisting of a single framework
or consistent family. A classical analogy for a spin-half particle and other
arguments show that the infinite amount of information needed to specify a
precise vector in its Hilbert space is not a measure of the information carried
by a quantum entity with a -dimensional Hilbert space; the latter is,
instead, bounded by log d bits (1 bit per qubit). The two bits of information
transmitted in dense coding are located not in one but in the correlation
between two qubits, consistent with this bound. A quantum channel can be
thought of as a "structure" or collection of frameworks, and the physical
location of the information in the individual frameworks can be used to
identify the location of the channel. Analysis of a quantum circuit used as a
model of teleportation shows that the location of the channel depends upon
which structure is employed; for ordinary teleportation it is not (contrary to
Deutsch and Hayden) present in the two bits resulting from the Bell-basis
measurement, but in correlations of these with a distant qubit. In neither
teleportation nor dense coding does information travel backwards in time, nor
is it transmitted by nonlocal (superluminal) influences. It is (tentatively)
proposed that all aspects of quantum information can in principle be understood
in terms of the (basically classical) behavior of information in a particular
framework, along with the framework dependence of this information.Comment: Latex 29 pages, uses PSTricks for figure
Phase Structure of 2-Flavor Quark Matter: Heterogeneous Superconductors
We analyze the free energy of charge and color neutral 2-flavor quark matter
within the BCS approximation. We consider both the homogeneous gapless
superconducting phase and the heterogeneous mixed phase where normal and BCS
superconducting phases coexist. We calculate the surface tension between normal
and superconducting phases and use it to compare the free energies of the
gapless and mixed phases. Our calculation, which retains only the leading order
gradient contribution to the free energy, indicates that the mixed phase is
energetically favored over an interesting range of densities of relevance to 2
flavor quark matter in neutron stars.Comment: 11 pages, 4 figures. Major Revisions. Includes a detailed discussion
of the kinetic terms of the effective theory, instabilities of the gapless
phase and the charge neutral phase diagra
Polarized Diffuse Emission at 2.3 GHz in a High Galactic Latitude Area
Polarized diffuse emission observations at 2.3 GHz in a high Galactic
latitude area are presented. The 2\degr X 2\degr field, centred in
(\alpha=5^h,\delta=-49\degr), is located in the region observed by the
BOOMERanG experiment. Our observations has been carried out with the Parkes
Radio telescope and represent the highest frequency detection done to date in
low emission areas. Because of a weaker Faraday rotation action, the high
frequency allows an estimate of the Galactic synchrotron contamination of the
Cosmic Microwave Background Polarization (CMBP) that is more reliable than that
done at 1.4 GHz. We find that the angular power spectra of the E- and B-modes
have slopes of \beta_E = -1.46 +/- 0.14 and \beta_B = -1.87 +/- 0.22,
indicating a flattening with respect to 1.4 GHz. Extrapolated up to 32 GHz, the
E-mode spectrum is about 3 orders of magnitude lower than that of the CMBP,
allowing a clean detection even at this frequency. The best improvement
concerns the B-mode, for which our single-dish observations provide the first
estimate of the contamination on angular scales close to the CMBP peak (about 2
degrees). We find that the CMBP B-mode should be stronger than synchrotron
contamination at 90 GHz for models with T/S > 0.01. This low level could move
down to 60-70 GHz the optimal window for CMBP measures.Comment: 5 pages, 6 figures, accepted for publication in MNRAS Letter
P,T-Violating Nuclear Matrix Elements in the One-Meson Exchange Approximation
Expressions for the P,T-violating NN potentials are derived for ,
and exchange. The nuclear matrix elements for and
exchange are shown to be greatly suppressed, so that, under the assumption of
comparable coupling constants, exchange would dominate by two orders of
magnitude. The ratio of P,T-violating to P-violating matrix elements is found
to remain approximately constant across the nuclear mass table, thus
establishing the proportionality between time-reversal-violation and
parity-violation matrix elements. The calculated values of this ratio suggest a
need to obtain an accuracy of order for the ratio of the
PT-violating to P-violating asymmetries in neutron transmission experiments in
order to improve on the present limits on the isovector pion coupling constant.Comment: 17 pages, LaTeX, no figure
Weak Lensing Determination of the Mass in Galaxy Halos
We detect the weak gravitational lensing distortion of 450,000 background
galaxies (20<R<23) by 790 foreground galaxies (R<18) selected from the Las
Campanas Redshift Survey (LCRS). This is the first detection of weak lensing by
field galaxies of known redshift, and as such permits us to reconstruct the
shear profile of the typical field galaxy halo in absolute physical units
(modulo H_0), and to investigate the dependence of halo mass upon galaxy
luminosity. This is also the first galaxy-galaxy lensing study for which the
calibration errors are negligible. Within a projected radius of 200 \hkpc, the
shear profile is consistent with an isothermal profile with circular velocity
164+-20 km/s for an L* galaxy, consistent with typical disk rotation at this
luminosity. This halo mass normalization, combined with the halo profile
derived by Fischer et al (2000) from lensing analysis SDSS data, places a lower
limit of (2.7+-0.6) x 10^{12}h^{-1} solar masses on the mass of an L* galaxy
halo, in good agreement with satellite galaxy studies. Given the known
luminosity function of LCRS galaxies, and the assumption that for galaxies, we determine that the mass within 260\hkpc of normal
galaxies contributes to the density of the Universe (for
) or for . These lensing data suggest
that (95% CL), only marginally in agreement with the usual
Faber-Jackson or Tully-Fisher scaling. This is the most
complete direct inventory of the matter content of the Universe to date.Comment: 18 pages, incl. 3 figures. Submitted to ApJ 6/7/00, still no response
from the referee after four months
Relation between Poisson and Schr\"odinger equation in one dimension
The relation between the Poisson and Schr\"odinger equation in one dimension
is obtained through a simple transformation. It is pointed out that this
analogy between both equations can be only applied for potentials that involve
a combination of attractive and repulsive delta function potentials. This
relationship enables us to use elementary electrostatic results to find the
exact solution of the associated quantum bound state problem in one dimension.
Particularly, the result shows that it is possible to trap a single electron in
a one dimensional ionic crystal.Comment: Revised versio
The absolute position of a resonance peak
It is common practice in scattering theory to correlate between the position
of a resonance peak in the cross section and the real part of a complex energy
of a pole of the scattering amplitude. In this work we show that the resonance
peak position appears at the absolute value of the pole's complex energy rather
than its real part. We further demonstrate that a local theory of resonances
can still be used even in cases previously thought impossible
Interaction between U/UO2 bilayers and hydrogen studied by in-situ X-ray diffraction
This paper reports experiments investigating the reaction of H with
uranium metal-oxide bilayers. The bilayers consist of 100 nm of
epitaxial -U (grown on a Nb buffer deposited on sapphire) with a
UO overlayer of thicknesses of between 20 and 80 nm. The oxides were made
either by depositing via reactive magnetron sputtering, or allowing the uranium
metal to oxidise in air at room temperature. The bilayers were exposed to
hydrogen, with sample temperatures between 80 and 200 C, and monitored via
in-situ x-ray diffraction and complimentary experiments conducted using
Scanning Transmission Electron Microscopy - Electron Energy Loss Spectroscopy
(STEM-EELS). Small partial pressures of H caused rapid consumption of the
U metal and lead to changes in the intensity and position of the diffraction
peaks from both the UO overlayers and the U metal. There is an
orientational dependence in the rate of U consumption. From changes in the
lattice parameter we deduce that hydrogen enters both the oxide and metal
layers, contracting the oxide and expanding the metal. The air-grown oxide
overlayers appear to hinder the H-reaction up to a threshold dose, but
then on heating from 80 to 140 C the consumption is more rapid than for the
as-deposited overlayers. STEM-EELS establishes that the U-hydride layer lies at
the oxide-metal interface, and that the initial formation is at defects or
grain boundaries, and involves the formation of amorphous and/or
nanocrystalline UH. This explains why no diffraction peaks from UH
are observed. {\textcopyright British Crown Owned Copyright 2017/AWE}Comment: Submitted for peer revie
Magnetic Moment Formation in Graphene Detected by Scattering of Pure Spin Currents
Hydrogen adatoms are shown to generate magnetic moments inside single layer
graphene. Spin transport measurements on graphene spin valves exhibit a dip in
the non-local spin signal as a function of applied magnetic field, which is due
to scattering (relaxation) of pure spin currents by exchange coupling to the
magnetic moments. Furthermore, Hanle spin precession measurements indicate the
presence of an exchange field generated by the magnetic moments. The entire
experiment including spin transport is performed in an ultrahigh vacuum
chamber, and the characteristic signatures of magnetic moment formation appear
only after hydrogen adatoms are introduced. Lattice vacancies also demonstrate
similar behavior indicating that the magnetic moment formation originates from
pz-orbital defects.Comment: accepted to Phys. Rev. Let
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