996 research outputs found
Probabilities from Entanglement, Born's Rule from Envariance
I show how probabilities arise in quantum physics by exploring implications
of {\it environment - assisted invariance} or {\it envariance}, a recently
discovered symmetry exhibited by entangled quantum systems. Envariance of
perfectly entangled ``Bell-like'' states can be used to rigorously justify
complete ignorance of the observer about the outcome of any measurement on
either of the members of the entangled pair. For more general states,
envariance leads to Born's rule, for the outcomes
associated with Schmidt states. Probabilities derived in this manner are an
objective reflection of the underlying state of the system -- they represent
experimentally verifiable symmetries, and not just a subjective ``state of
knowledge'' of the observer. Envariance - based approach is compared with and
found superior to pre-quantum definitions of probability including the {\it
standard definition} based on the `principle of indifference' due to Laplace,
and the {\it relative frequency approach} advocated by von Mises. Implications
of envariance for the interpretation of quantum theory go beyond the derivation
of Born's rule: Envariance is enough to establish dynamical independence of
preferred branches of the evolving state vector of the composite system, and,
thus, to arrive at the {\it environment - induced superselection (einselection)
of pointer states}, that was usually derived by an appeal to decoherence.
Envariant origin of Born's rule for probabilities sheds a new light on the
relation between ignorance (and hence, information) and the nature of quantum
states.Comment: Figure and an appendix (Born's rule for continuous spectra) added.
Presentation improved. (Comments still welcome...
Ferromagnetic Liquid Thin Films Under Applied Field
Theoretical calculations, computer simulations and experiments indicate the
possible existence of a ferromagnetic liquid state, although definitive
experimental evidence is lacking. Should such a state exist, demagnetization
effects would force a nontrivial magnetization texture. Since liquid droplets
are deformable, the droplet shape is coupled with the magnetization texture. In
a thin-film geometry in zero applied field, the droplet has a circular shape
and a rotating magnetization texture with a point vortex at the center. We
calculate the elongation and magnetization texture of such ferromagnetic thin
film liquid droplet confined between two parallel plates under a weak applied
magnetic field. The vortex stretches into a domain wall and exchange forces
break the reflection symmetry. This behavior contrasts qualitatively and
quantitatively with the elongation of paramagnetic thin films.Comment: 10 pages, 4 figures, Submitted to Phys. Rev.
Multicomplementary operators via finite Fourier transform
A complete set of d+1 mutually unbiased bases exists in a Hilbert spaces of
dimension d, whenever d is a power of a prime. We discuss a simple construction
of d+1 disjoint classes (each one having d-1 commuting operators) such that the
corresponding eigenstates form sets of unbiased bases. Such a construction
works properly for prime dimension. We investigate an alternative construction
in which the real numbers that label the classes are replaced by a finite field
having d elements. One of these classes is diagonal, and can be mapped to
cyclic operators by means of the finite Fourier transform, which allows one to
understand complementarity in a similar way as for the position-momentum pair
in standard quantum mechanics. The relevant examples of two and three qubits
and two qutrits are discussed in detail.Comment: 15 pages, no figure
Large two-level magnetoresistance effect in doped manganite grain boundary junctions
We performed a systematic analysis of the tunneling magnetoresistance (TMR)
effect in single grain boundary junctions formed in epitaxial
La(2/3)Ca(1/3)MnO(3) films deposited on SrTiO(3) bicrystals. For magnetic
fields H applied parallel to the grain boundary barrier, an ideal two-level
resistance switching behavior with sharp transitions is observed with a TMR
effect of up to 300% at 4.2 K and still above 100% at 77 K. Varying the angle
between H and the grain boundary results in differently shaped resistance vs H
curves. The observed behavior is explained within a model of magnetic domain
pinning at the grain boundary interface.Comment: 4 pages, 3 figures, to appear in Phys. Rev. B (Rapid Comm.
GPU-based ultra fast dose calculation using a finite pencil beam model
Online adaptive radiation therapy (ART) is an attractive concept that
promises the ability to deliver an optimal treatment in response to the
inter-fraction variability in patient anatomy. However, it has yet to be
realized due to technical limitations. Fast dose deposit coefficient
calculation is a critical component of the online planning process that is
required for plan optimization of intensity modulated radiation therapy (IMRT).
Computer graphics processing units (GPUs) are well-suited to provide the
requisite fast performance for the data-parallel nature of dose calculation. In
this work, we develop a dose calculation engine based on a finite-size pencil
beam (FSPB) algorithm and a GPU parallel computing framework. The developed
framework can accommodate any FSPB model. We test our implementation on a case
of a water phantom and a case of a prostate cancer patient with varying beamlet
and voxel sizes. All testing scenarios achieved speedup ranging from 200~400
times when using a NVIDIA Tesla C1060 card in comparison with a 2.27GHz Intel
Xeon CPU. The computational time for calculating dose deposition coefficients
for a 9-field prostate IMRT plan with this new framework is less than 1 second.
This indicates that the GPU-based FSPB algorithm is well-suited for online
re-planning for adaptive radiotherapy.Comment: submitted Physics in Medicine and Biolog
On plexus representation of dissimilarities
Correspondence analysis has found widespread application in analysing vegetation gradients. However, it is not clear how it is robust to situations where structures other than a simple gradient exist. The introduction of instrumental variables in canonical correspondence analysis does not avoid these difficulties. In this paper I propose to examine some simple methods based on the notion of the plexus (sensu McIntosh) where graphs or networks are used to display some of the structure of the data so that an informed choice of models is possible. I showthat two different classes of plexus model are available. These classes are distinguished by the use in one case of a global Euclidean model to obtain well-separated pair decomposition (WSPD) of a set of points which implicitly involves all dissimilarities, while in the other a Riemannian view is taken and emphasis is placed locally, i.e., on small dissimilarities. I showan example of each of these classes applied to vegetation data
Ferromagnetic semiconductors
The current status and prospects of research on ferromagnetism in
semiconductors are reviewed. The question of the origin of ferromagnetism in
europium chalcogenides, chromium spinels and, particularly, in diluted magnetic
semiconductors is addressed. The nature of electronic states derived from 3d of
magnetic impurities is discussed in some details. Results of a quantitative
comparison between experimental and theoretical results, notably for Mn-based
III-V and II-VI compounds, are presented. This comparison demonstrates that the
current theory of the exchange interactions mediated by holes in the valence
band describes correctly the values of Curie temperatures T_C magnetic
anisotropy, domain structure, and magnetic circular dichroism. On this basis,
chemical trends are examined and show to lead to the prediction of
semiconductor systems with T_C that may exceed room temperature, an expectation
that are being confirmed by recent findings. Results for materials containing
magnetic ions other than Mn are also presented emphasizing that the double
exchange involving hoping through d states may operate in those systems.Comment: 18 pages, 8 figures; special issue of Semicon. Sci. Technol. on
semiconductor spintronic
Sensitivity of the IceCube Detector to Astrophysical Sources of High Energy Muon Neutrinos
We present the results of a Monte-Carlo study of the sensitivity of the
planned IceCube detector to predicted fluxes of muon neutrinos at TeV to PeV
energies. A complete simulation of the detector and data analysis is used to
study the detector's capability to search for muon neutrinos from sources such
as active galaxies and gamma-ray bursts. We study the effective area and the
angular resolution of the detector as a function of muon energy and angle of
incidence. We present detailed calculations of the sensitivity of the detector
to both diffuse and pointlike neutrino emissions, including an assessment of
the sensitivity to neutrinos detected in coincidence with gamma-ray burst
observations. After three years of datataking, IceCube will have been able to
detect a point source flux of E^2*dN/dE = 7*10^-9 cm^-2s^-1GeV at a 5-sigma
significance, or, in the absence of a signal, place a 90% c.l. limit at a level
E^2*dN/dE = 2*10^-9 cm^-2s^-1GeV. A diffuse E-2 flux would be detectable at a
minimum strength of E^2*dN/dE = 1*10^-8 cm^-2s^-1sr^-1GeV. A gamma-ray burst
model following the formulation of Waxman and Bahcall would result in a 5-sigma
effect after the observation of 200 bursts in coincidence with satellite
observations of the gamma-rays.Comment: 33 pages, 13 figures, 6 table
The unexpected resurgence of Weyl geometry in late 20-th century physics
Weyl's original scale geometry of 1918 ("purely infinitesimal geometry") was
withdrawn by its author from physical theorizing in the early 1920s. It had a
comeback in the last third of the 20th century in different contexts: scalar
tensor theories of gravity, foundations of gravity, foundations of quantum
mechanics, elementary particle physics, and cosmology. It seems that Weyl
geometry continues to offer an open research potential for the foundations of
physics even after the turn to the new millennium.Comment: Completely rewritten conference paper 'Beyond Einstein', Mainz Sep
2008. Preprint ELHC (Epistemology of the LHC) 2017-02, 92 pages, 1 figur
Detection of Atmospheric Muon Neutrinos with the IceCube 9-String Detector
The IceCube neutrino detector is a cubic kilometer TeV to PeV neutrino
detector under construction at the geographic South Pole. The dominant
population of neutrinos detected in IceCube is due to meson decay in cosmic-ray
air showers. These atmospheric neutrinos are relatively well-understood and
serve as a calibration and verification tool for the new detector. In 2006, the
detector was approximately 10% completed, and we report on data acquired from
the detector in this configuration. We observe an atmospheric neutrino signal
consistent with expectations, demonstrating that the IceCube detector is
capable of identifying neutrino events. In the first 137.4 days of livetime,
234 neutrino candidates were selected with an expectation of 211 +/-
76.1(syst.) +/- 14.5(stat.) events from atmospheric neutrinos
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