15,456 research outputs found
Triplet Superconductors from the Viewpoint of Basic Elements for Quantum Computers
We discuss possibilities of utilizing superconductors with Cooper condensates
in triplet pairing states (where the spin of condensate pairs is S=1) for
practical realization of quantum computers. Superconductors with triplet
pairing condensates have features that are unique and cannot be found in the
usual (singlet pairing, S=0) superconductors. The symmetry of the order
parameter in some triplet superconductors (e.g., ruthenates) corresponds to
doubly-degenerate chiral states. These states can serve as qubit base states
for quantum computing.Comment: 4 pages, 5 figures, will be presented at ASC-2002 and submitted to
IEEE Trans. Appl. Supercon
Theory of phaselock techniques as applied to aerospace transponders
Phaselock techniques as applied to aerospace transponder
Simulating Quantum Mechanics by Non-Contextual Hidden Variables
No physical measurement can be performed with infinite precision. This leaves
a loophole in the standard no-go arguments against non-contextual hidden
variables. All such arguments rely on choosing special sets of
quantum-mechanical observables with measurement outcomes that cannot be
simulated non-contextually. As a consequence, these arguments do not exclude
the hypothesis that the class of physical measurements in fact corresponds to a
dense subset of all theoretically possible measurements with outcomes and
quantum probabilities that \emph{can} be recovered from a non-contextual hidden
variable model. We show here by explicit construction that there are indeed
such non-contextual hidden variable models, both for projection valued and
positive operator valued measurements.Comment: 15 pages. Journal version. Only minor typo corrections from last
versio
Spectro-Morphology of Galaxies
We present a quantitative method to classify galaxies, based on
multi-wavelength data and elaborated from the properties of nearby galaxies.
Our objective is to define an evolutionary method that can be used for low and
high redshift objects. We estimate the concentration of light (C) at the galaxy
center and the 180 degree-rotational asymmetry (A), computed at several
wavelengths, from ultraviolet (UV) to I-band. The variation of the indices of
concentration and asymmetry with the wavelength reflects the proportion and the
distribution of young and old stellar populations in galaxies. In general C is
found to decrease from optical to UV, and A is found to increase from optical
to UV: the patchy appearance of galaxies in UV with no bulge is often very
different from their counterpart at optical wavelengths, with prominent bulges
and more regular disks. The variation of C and A with the wavelength is
quantified. By this way, we are able to distinguish five types of galaxies that
we call spectro-morphological types: compact, ringed, spiral, irregular and
central-starburst galaxies, which can be differentiated by the repartition of
their stellar populations. We discuss in detail the morphology of galaxies of
the sample, and describe the morphological characteristics of each
spectro-morphological type. We apply spectro-morphology to three objects at a
redshift z=1 in the Hubble Deep Field North, that gives encouraging results for
applications to large samples of high-redshift galaxies. This method of
morphological classification could be used to study the evolution of the
morphology with the redshift and is expected to bring observational constraints
on scenarios of galaxy evolution.Comment: Accepted for publication in Astronomy & Astrophysic
New geometries for high spatial resolution hall probes
The Hall response function of symmetric and asymmetric planar Hall effect
devices is investigated by scanning a magnetized tip above a sensor surface
while simultaneously recording the topography and the Hall voltage. Hall sensor
geometries are tailored using a Focused Ion Beam, in standard symmetric and new
asymmetric geometries. With this technique we are able to reduce a single
voltage probe to a narrow constriction 20 times smaller than the other device
dimensions. We show that the response function is peaked above the
constriction, in agreement with numerical simulations. The results suggest a
new way to pattern Hall sensors for enhanced spatial resolution.Comment: 12 pages, 5 figures, submitted to Journal of Applied Physic
SAGE measurements of the stratospheric aerosol dispersion and loading from the Soufriere Volcano
Explosions of the Soufriere volcano on the Caribbean Island of St. Vincent reduced two major stratospheric plumes which the stratospheric aerosol and gas experiment (SAGE) satellite tracked to West Africa and the North Atlantic Ocean. The total mass of the stratospheric ejecta measured is less than 0.5% of the global stratospheric aerosol burden. No significant temperature or climate perturbation is expected. It is found that the movement and dispersion of the plumes agree with those deduced from high altitude meteorological data and dispersion theory. The stratospheric aerosol dispersion and loading from the Soufrier volcano was measured
Pre- and Post-selection paradoxes and contextuality in quantum mechanics
Many seemingly paradoxical effects are known in the predictions for outcomes
of intermediate measurements made on pre- and post-selected quantum systems.
Despite appearances, these effects do not demonstrate the impossibility of a
noncontextual hidden variable theory, since an explanation in terms of
measurement-disturbance is possible. Nonetheless, we show that for every
paradoxical effect wherein all the pre- and post- selected probabilities are 0
or 1 and the pre- and post-selected states are nonorthogonal, there is an
associated proof of contextuality. This proof is obtained by considering all
the measurements involved in the paradoxical effect -- the pre-selection, the
post-selection, and the alternative possible intermediate measurements -- as
alternative possible measurements at a single time.Comment: 5 pages, 1 figure. Submitted to Phys. Rev. Lett. v2.0 revised in the
light of referee comments, results unchange
Magnetoresistance due to Domain Walls in Micron Scale Fe Wires with Stripe Domains
The magnetoresistance (MR) associated with domain boundaries has been
investigated in microfabricated bcc Fe (0.65 to 20 m linewidth) wires with
controlled stripe domains. Domain configurations have been characterized using
magnetic force microscopy. MR measurements as a function of field angle,
temperature and domain configuration are used to estimate MR contributions due
to resistivity anisotropy and domain walls. Evidence is presented that domain
boundaries enhance the conductivity in such microstructures over a broad range
of temperatures (1.5 K to 80 K).Comment: 8 pages, 3 postscript figures, and 2 jpg images (Fig 1 and 2) to
appear in IEEE Transactions on Magnetics (Fall 1998
Coin Tossing is Strictly Weaker Than Bit Commitment
We define cryptographic assumptions applicable to two mistrustful parties who
each control two or more separate secure sites between which special relativity
guarantees a time lapse in communication. We show that, under these
assumptions, unconditionally secure coin tossing can be carried out by
exchanges of classical information. We show also, following Mayers, Lo and
Chau, that unconditionally secure bit commitment cannot be carried out by
finitely many exchanges of classical or quantum information. Finally we show
that, under standard cryptographic assumptions, coin tossing is strictly weaker
than bit commitment. That is, no secure classical or quantum bit commitment
protocol can be built from a finite number of invocations of a secure coin
tossing black box together with finitely many additional information exchanges.Comment: Final version; to appear in Phys. Rev. Let
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