11,139 research outputs found
Implementable Quantum Bit-String Commitment Protocol
Quantum bit-string commitment[A.Kent, Phys.Rev.Lett., 90, 237901 (2003)] or
QBSC is a variant of bit commitment (BC). In this paper, we propose a new QBSC
protocol that can be implemented using currently available technology, and
prove its security under the same security criteria as discussed by Kent. QBSC
is a generalization of BC, but has slightly weaker requirements, and our
proposed protocol is not intended to break the no-go theorem of quantum BC.Comment: To appear in Phys. Rev. A., 9 pages, 2 figure
A method of enciphering quantum states
In this paper, we propose a method of enciphering quantum states of two-state
systems (qubits) for sending them in secrecy without entangled qubits shared by
two legitimate users (Alice and Bob). This method has the following two
properties. First, even if an eavesdropper (Eve) steals qubits, she can extract
information from them with certain probability at most. Second, Alice and Bob
can confirm that the qubits are transmitted between them correctly by measuring
a signature. If Eve measures m qubits one by one from n enciphered qubits and
sends alternative ones (the Intercept/Resend attack), a probability that Alice
and Bob do not notice Eve's action is equal to (3/4)^m or less. Passwords for
decryption and the signature are given by classical binary strings and they are
disclosed through a public channel. Enciphering classical information by this
method is equivalent to the one-time pad method with distributing a classical
key (random binary string) by the BB84 protocol. If Eve takes away qubits,
Alice and Bob lose the original quantum information. If we apply our method to
a state in iteration, Eve's success probability decreases exponentially. We
cannot examine security against the case that Eve makes an attack with using
entanglement. This remains to be solved in the future.Comment: 21 pages, Latex2e, 10 epsf figures. v2: 22 pages, added two
references, several clarifying sentences are added in Sec. 5, typos
corrected, a new proof is provided in Appendix A and it is shorter than the
old one. v3: 23 pages, one section is adde
Quantifying nonorthogonality
An exploratory approach to the possibility of analyzing nonorthogonality as a
quantifiable property is presented. Three different measures for the
nonorthogonality of pure states are introduced, and one of these measures is
extended to single-particle density matrices using methods that are similar to
recently introduced techniques for quantifying entanglement. Several
interesting special cases are considered. It is pointed out that a measure of
nonorthogonality can meaningfully be associated with a single mixed quantum
state. It is then shown how nonorthogonality can be unlocked with classical
information; this analysis reveals interesting inequalities and points to a
number of connections between nonorthogonality and entanglement.Comment: Accepted for publication in Phys. Rev.
COMPTEL Observations of the Gamma-Ray Blazar PKS 1622-297
We report results of observations and analyses on the gamma-ray blazar PKS
1622-297, with emphasis on the COMPTEL data (0.75 - 30 MeV) collected between
April 1991 and November 1997. PKS 1622-297 was detected as a source of
gamma-rays by the EGRET experiment aboard CGRO in 1995 during a gamma-ray
outburst at energies above 100 MeV lasting for five weeks.
In this time period the blazar was significantly (~ 5.9 sigma) detected by
COMPTEL at 10-30 MeV. At lower COMPTEL energies the detection is marginal,
resulting in a hard MeV spectrum.
The combined COMPTEL/EGRET energy spectrum shows a break at MeV energies. The
broad-band spectrum (radio - gamma-rays) shows that the gamma-ray emission
dominates the overall power output. On top of the 5-week gamma-ray outburst,
EGRET detected a huge flare lasting for > 1 day. Enhanced MeV emission (10 - 30
MeV) is found near the time of this flare, suggesting a possible time delay
with respect to the emission above 100 MeV. Outside the 5-week flaring period
in 1995, we do not detect MeV emission from PKS 1622-297.Comment: 10 pages including 9 figures, accepted for publication in A&
A holistic inverse approach based on a multi-objective function optimisation model to recover elastic-plastic properties of materials from the depth-sensing indentation test
Recent years have seen an increased interest in the mechanical characterisation of materials via the inverse analysis of depth-sensing indentation data; however, at low-loads both the reaction forces measured by the instrument and the contact evolution at the indenter-material interface may be severely affected by indentation size effects (ISEs). Notwithstanding the knowledge of ISE, the inverse analyses proposed to date have failed to investigate the divergence between the small-scale properties measured via indentation and the large-scale properties extracted from other techniques, e.g. tensile testing. Therefore, this study investigates the sensitivity of an inverse analysis methodology to the indentation size in relation to the size of the microstructure. The proposed inverse analysis approach is based on a multi-objective function (MOF) optimisation model that finds the combination of material properties (Young's modulus, yield stress and strain-hardening exponent) that provides the best fit to both the experimental load-displacement (P-h) curve extracted from the indentation instrument and pile-up profile of the residual imprint measured with an atomic force microscope. Therefore, the piling-up/sinking-in effect, which is strongly linked to the plastic hardening behaviour of the indented material, is considered to address the non-uniqueness issue of the inverse analysis of indentation. A Berkovich indenter was used to measure the near surface properties of three different materials, including a titanium alloy (Ti-6Al-4 V), chromium-molybdenum-vanadium steel (CrMoV) and high purity copper (C110); materials have been selected to represent a wide range of ductile metallic materials so as to assess the generality of the MOF model
COMPTEL observations of the Virgo blazars 3C 273 and 3C 279
We report the main MeV properties (detections, light curves, spectra) of the Virgo blazars 3C 273 and 3C 279 which were derived from a consistent analysis of all COMPTEL Virgo observations between 1991 and 1997
COMPTEL observations of the blazars 3C 454.3 and CTA 102
We have analyzed the two blazars of 3C 454.3 and CTA 102 using all available COMPTEL data from 1991 to 1999. In the 10–30 MeV band, emission from the general direction of the sources is found at the 4σ-level, being consistent with contributions from both sources. Below 10 MeV only 3C 454.3 is significantly detected, with the strongest evidence (5.6 σ) in the 3–10 MeV band. Significant flux variability is not observed for both sources, while a low emission is seen most of the years in the 3–10 MeV light curve for 3C 454.3. Its time-averaged MeV spectrum suggests a power maximum between 3 to 10 MeV
Administering Colorado’s Water: A Critique of the Present Approach
41 pages.
Contains footnotes
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