1,431 research outputs found
Passive decoy state quantum key distribution: Closing the gap to perfect sources
We propose a quantum key distribution scheme which closely matches the
performance of a perfect single photon source. It nearly attains the physical
upper bound in terms of key generation rate and maximally achievable distance.
Our scheme relies on a practical setup based on a parametric downconversion
source and present-day, non-ideal photon-number detection. Arbitrary
experimental imperfections which lead to bit errors are included. We select
decoy states by classical post-processing. This allows to improve the effective
signal statistics and achievable distance.Comment: 4 pages, 3 figures. State preparation correcte
Quantum Cryptography Based on the Time--Energy Uncertainty Relation
A new cryptosystem based on the fundamental time--energy uncertainty relation
is proposed. Such a cryptosystem can be implemented with both correlated photon
pairs and single photon states.Comment: 5 pages, LaTex, no figure
Modeling the Daily Variations of the Coronal X-ray Spectral Irradiance with Two Temperatures and Two Emission Measures
The Miniature X-ray Solar Spectrometer (MinXSS-1) CubeSat observed solar
X-rays between 0.5 and 10 keV. A two-temperature, two-emission measure model is
fit to each daily averaged spectrum. These daily average temperatures and
emission measures are plotted against the corresponding daily solar 10.7 cm
radio flux (F10.7) value and a linear correlation is found between each that we
call the Schwab Woods Mason (SWM) model. The linear trends show that one can
estimate the solar spectrum between 0.5 keV and 10 keV based on the F10.7
measurement alone. The cooler temperature component of this model represents
the quiescent sun contribution to the spectra and is essentially independent of
solar activity, meaning the daily average quiescent sun is accurately described
by a single temperature (1.70 MK) regardless of solar intensity and only the
emission measure corresponding to this temperature needs to be adjusted for
higher or lower solar intensity. The warmer temperature component is shown to
represent active region contributions to the spectra and varies between 5 MK to
6 MK. GOES XRS-B data between 1-8 Angstroms is used to validate this model and
it is found that the ratio between the SWM model irradiance and the GOES XRS-B
irradiance is close to unity on average. MinXSS-1 spectra during quiescent
solar conditions have very low counts beyond around 3 keV. The SWM model can
generate MinXSS-1 or DAXSS spectra at very high spectral resolution and with
extended energy ranges to fill in gaps between measurements and extend
predictions back to 1947
Interpolation of Hilbert and Sobolev Spaces: Quantitative Estimates and Counterexamples
This paper provides an overview of interpolation of Banach and Hilbert
spaces, with a focus on establishing when equivalence of norms is in fact
equality of norms in the key results of the theory. (In brief, our conclusion
for the Hilbert space case is that, with the right normalisations, all the key
results hold with equality of norms.) In the final section we apply the Hilbert
space results to the Sobolev spaces and
, for and an open . We exhibit examples in one and two dimensions of sets
for which these scales of Sobolev spaces are not interpolation scales. In the
cases when they are interpolation scales (in particular, if is
Lipschitz) we exhibit examples that show that, in general, the interpolation
norm does not coincide with the intrinsic Sobolev norm and, in fact, the ratio
of these two norms can be arbitrarily large
Using of small-scale quantum computers in cryptography with many-qubit entangled states
We propose a new cryptographic protocol. It is suggested to encode
information in ordinary binary form into many-qubit entangled states with the
help of a quantum computer. A state of qubits (realized, e.g., with photons) is
transmitted through a quantum channel to the addressee, who applies a quantum
computer tuned to realize the inverse unitary transformation decoding of the
message. Different ways of eavesdropping are considered, and an estimate of the
time needed for determining the secret unitary transformation is given. It is
shown that using even small quantum computers can serve as a basis for very
efficient cryptographic protocols. For a suggested cryptographic protocol, the
time scale on which communication can be considered secure is exponential in
the number of qubits in the entangled states and in the number of gates used to
construct the quantum network
Quantum state transfer and entanglement distribution among distant nodes in a quantum network
We propose a scheme to utilize photons for ideal quantum transmission between
atoms located at spatially-separated nodes of a quantum network. The
transmission protocol employs special laser pulses which excite an atom inside
an optical cavity at the sending node so that its state is mapped into a
time-symmetric photon wavepacket that will enter a cavity at the receiving node
and be absorbed by an atom there with unit probability. Implementation of our
scheme would enable reliable transfer or sharing of entanglement among
spatially distant atoms.Comment: 4 pages, 3 postscript figure
Multiphoton localization and propagating quantum gap solitons in a frequency gap medium
The many-particle spectrum of an isotropic frequency gap medium doped with
impurity resonance atoms is studied using the Bethe ansatz technique. The
spectrum is shown to contain pairs of quantum correlated ``gap excitations''
and their heavy bound complexes (``gap solitons''), enabling the propagation of
quantum information within the classically forbidden gap. In addition,
multiparticle localization of the radiation and the medium polarization occurs
when such a gap soliton is pinned to the impurity atom.Comment: 8 pages, RevTEX, to appear in Phys. Rev. Let
Neutrinos in a spherical box
In the present paper we study some neutrino properties as they may appear in
the low energy neutrinos emitted in triton decay with maximum neutrino energy
of 18.6 keV. The technical challenges to this end can be achieved by building a
very large TPC capable of detecting low energy recoils, down to a a few tenths
of a keV, within the required low background constraints. More specifically We
propose the development of a spherical gaseous TPC of about 10-m in radius and
a 200 Mcurie triton source in the center of curvature. One can list a number of
exciting studies, concerning fundamental physics issues, that could be made
using a large volume TPC and low energy antineutrinos: 1) The oscillation
length involving the small angle of the neutrino mixing matrix, directly
measured in this disappearance experiment, is fully contained inside the
detector. Measuring the counting rate of neutrino-electron elastic scattering
as a function of the distance of the source will give a precise and unambiguous
measurement of the oscillation parameters free of systematic errors. In fact
first estimates show that even with a year's data taking a sensitivity of a few
percent for the measurement of the above angle will be achieved. 2) The low
energy detection threshold offers a unique sensitivity for the neutrino
magnetic moment which is about two orders of magnitude beyond the current
experimental limit. 3) Scattering at such low neutrino energies has never been
studied and any departure from the expected behavior may be an indication of
new physics beyond the standard model. In this work we mainly focus on the
various theoretical issues involved including a precise determination of the
Weinberg angle at very low momentum transfer.Comment: 16 Pages, LaTex, 7 figures, talk given at NANP 2003, Dubna, Russia,
June 23, 200
Fractional smoothness and applications in finance
This overview article concerns the notion of fractional smoothness of random
variables of the form , where is a certain
diffusion process. We review the connection to the real interpolation theory,
give examples and applications of this concept. The applications in stochastic
finance mainly concern the analysis of discrete time hedging errors. We close
the review by indicating some further developments.Comment: Chapter of AMAMEF book. 20 pages
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