3,243 research outputs found
Simulation Subsumption or Déjà vu on the Web
Simulation unification is a special kind of unification adapted to retrieving semi-structured data on the Web. This article introduces simulation subsumption, or containment, that is, query subsumption under simulation unification. Simulation subsumption is crucial in general for query optimization, in particular for optimizing pattern-based search engines, and for the termination of recursive rule-based web languages such as the XML and RDF query language Xcerpt. This paper first motivates and formalizes simulation subsumption. Then, it establishes decidability of simulation subsumption for advanced query patterns featuring descendant constructs, regular expressions, negative subterms (or subterm exclusions), and multiple variable occurrences. Finally, we show that subsumption between two query terms can be decided in O(n!n) where n is the sum of the sizes of both query terms
Quantum circuit for security proof of quantum key distribution without encryption of error syndrome and noisy processing
One of the simplest security proofs of quantum key distribution is based on
the so-called complementarity scenario, which involves the complementarity
control of an actual protocol and a virtual protocol [M. Koashi, e-print
arXiv:0704.3661 (2007)]. The existing virtual protocol has a limitation in
classical postprocessing, i.e., the syndrome for the error-correction step has
to be encrypted. In this paper, we remove this limitation by constructing a
quantum circuit for the virtual protocol. Moreover, our circuit with a shield
system gives an intuitive proof of why adding noise to the sifted key increases
the bit error rate threshold in the general case in which one of the parties
does not possess a qubit. Thus, our circuit bridges the simple proof and the
use of wider classes of classical postprocessing.Comment: 8 pages, 2 figures. Typo correcte
Unconditionally secure key distillation from multi-photons
In this paper, we prove that the unconditionally secure key can be
surprisingly extracted from {\it multi}-photon emission part in the photon
polarization-based QKD. One example is shown by explicitly proving that one can
indeed generate an unconditionally secure key from Alice's two-photon emission
part in ``Quantum cryptography protocols robust against photon number splitting
attacks for weak laser pulses implementations'' proposed by V. Scarani {\it et
al.,} in Phys. Rev. Lett. {\bf 92}, 057901 (2004), which is called SARG04. This
protocol uses the same four states as in BB84 and differs only in the classical
post-processing protocol. It is, thus, interesting to see how the classical
post-processing of quantum key distribution might qualitatively change its
security. We also show that one can generate an unconditionally secure key from
the single to the four-photon part in a generalized SARG04 that uses six
states. Finally, we also compare the bit error rate threshold of these
protocols with the one in BB84 and the original six-state protocol assuming a
depolarizing channel.Comment: The title has changed again. We considerably improved our
presentation, and furthermore we proposed & analyzed a security of a modified
SARG04 protocol, which uses six state
Unconditionally Secure Key Distribution Based on Two Nonorthogonal States
We prove the unconditional security of the Bennett 1992 protocol, by using a
reduction to an entanglement distillation protocol initiated by a local
filtering process. The bit errors and the phase errors are correlated after the
filtering, and we can bound the amount of phase errors from the observed bit
errors by an estimation method involving nonorthogonal measurements. The angle
between the two states shows a trade-off between accuracy of the estimation and
robustness to noises.Comment: 5 pages, 1 figur
Internal structure of Skyrme black hole
We consider the internal structure of the Skyrme black hole under a static
and spherically symmetric ansatz. $@u8(Be concentrate on solutions with the
node number one and with the "winding" number zero, where there exist two
solutions for each horizon radius; one solution is stable and the other is
unstable against linear perturbation. We find that a generic solution exhibits
an oscillating behavior near the sigularity, as similar to a solution in the
Einstein-Yang-Mills (EYM) system, independently to stability of the solution.
Comparing it with that in the EYM system, this oscillation becomes mild because
of the mass term of the Skyrme field. We also find Schwarzschild-like
exceptional solutions where no oscillating behavior is seen. Contrary to the
EYM system where there is one such solution branch if the node number is fixed,
there are two branches corresponding to the stable and the unstable ones.Comment: 5 pages, 4 figures, some contents adde
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