466 research outputs found
Experimentally Feasible Security Check for n-qubit Quantum Secret Sharing
In this article we present a general security strategy for quantum secret
sharing (QSS) protocols based on the HBB scheme presented by Hillery, Bu\v{z}ek
and Berthiaume [Phys. Rev A \textbf{59}, 1829 (1999)]. We focus on a
generalization of the HBB protocol to communication parties thus including
-partite GHZ states. We show that the multipartite version of the HBB scheme
is insecure in certain settings and impractical when going to large . To
provide security for such QSS schemes in general we use the framework presented
by some of the authors [M. Huber, F. Minert, A. Gabriel, B. C. Hiesmayr, Phys.
Rev. Lett. \textbf{104}, 210501 (2010)] to detect certain genuine partite
entanglement between the communication parties. In particular, we present a
simple inequality which tests the security.Comment: 5 pages, submitted to Phys. Rev.
Economical (k,m)-threshold controlled quantum teleportation
We study a (k,m)-threshold controlling scheme for controlled quantum
teleportation. A standard polynomial coding over GF(p) with prime p > m-1 needs
to distribute a d-dimensional qudit with d >= p to each controller for this
purpose. We propose a scheme using m qubits (two-dimensional qudits) for the
controllers' portion, following a discussion on the benefit of a quantum
control in comparison to a classical control of a quantum teleportation.Comment: 11 pages, 2 figures, v2: minor revision, discussions improved, an
equation corrected in procedure (A) of section 4.3, v3: major revision,
protocols extended, citations added, v4: minor grammatical revision, v5:
minor revision, discussions extende
Matroids and Quantum Secret Sharing Schemes
A secret sharing scheme is a cryptographic protocol to distribute a secret
state in an encoded form among a group of players such that only authorized
subsets of the players can reconstruct the secret. Classically, efficient
secret sharing schemes have been shown to be induced by matroids. Furthermore,
access structures of such schemes can be characterized by an excluded minor
relation. No such relations are known for quantum secret sharing schemes. In
this paper we take the first steps toward a matroidal characterization of
quantum secret sharing schemes. In addition to providing a new perspective on
quantum secret sharing schemes, this characterization has important benefits.
While previous work has shown how to construct quantum secret sharing schemes
for general access structures, these schemes are not claimed to be efficient.
In this context the present results prove to be useful; they enable us to
construct efficient quantum secret sharing schemes for many general access
structures. More precisely, we show that an identically self-dual matroid that
is representable over a finite field induces a pure state quantum secret
sharing scheme with information rate one
Symmetric multiparty-controlled teleportation of an arbitrary two-particle entanglement
We present a way for symmetric multiparty-controlled teleportation of an
arbitrary two-particle entangled state based on Bell-basis measurements by
using two Greenberger-Horne-Zeilinger states, i.e., a sender transmits an
arbitrary two-particle entangled state to a distant receiver, an arbitrary one
of the agents via the control of the others in a network. It will be
shown that the outcomes in the cases that is odd or it is even are
different in principle as the receiver has to perform a controlled-not
operation on his particles for reconstructing the original arbitrary entangled
state in addition to some local unitary operations in the former. Also we
discuss the applications of this controlled teleporation for quantum secret
sharing of classical and quantum information. As all the instances can be used
to carry useful information, its efficiency for qubits approaches the maximal
value.Comment: 9 pages, 3 figures; the revised version published in Physical Review
A 72, 022338 (2005). The detail for setting up a GHZ-state quantum channel is
adde
Circular quantum secret sharing
A circular quantum secret sharing protocol is proposed, which is useful and
efficient when one of the parties of secret sharing is remote to the others who
are in adjacent, especially the parties are more than three. We describe the
process of this protocol and discuss its security when the quantum information
carrying is polarized single photons running circularly. It will be shown that
entanglement is not necessary for quantum secret sharing. Moreover, the
theoretic efficiency is improved to approach 100% as almost all the instances
can be used for generating the private key, and each photon can carry one bit
of information without quantum storage. It is straightforwardly to utilize this
topological structure to complete quantum secret sharing with multi-level
two-particle entanglement in high capacity securely.Comment: 7 pages, 2 figure
Efficient symmetric multiparty quantum state sharing of an arbitrary m-qubit state
We present a scheme for symmetric multiparty quantum state sharing of an
arbitrary -qubit state with Greenberger-Horne-Zeilinger states following
some ideas from the controlled teleportation [Phys. Rev. A \textbf{72}, 02338
(2005)]. The sender Alice performs Bell-state measurements on her
particles and the controllers need only to take some single-photon product
measurements on their photons independently, not Bell-state measurements, which
makes this scheme more convenient than the latter. Also it does not require the
parties to perform a controlled-NOT gate on the photons for reconstructing the
unknown -qubit state and it is an optimal one as its efficiency for qubits
approaches the maximal value.Comment: 6 pages, no figures; It simplifies the process for sharing an
arbitrary m-qubit state in Phys. Rev. A 72, 022338 (2005) (quant-ph/0501129
A simple combinatorial treatment of constructions and threshold gaps of ramp schemes
We give easy proofs of some recent results concerning threshold gaps in ramp schemes. We then generalise a construction method for ramp schemes employing error-correcting codes so that it can be applied using nonlinear (as well as linear) codes. Finally, as an immediate consequence of these results, we provide a new explicit bound on the minimum length of a code having a specified distance and dual distance
Cancer risks from arsenic in drinking water.
Ingestion of arsenic, both from water supplies and medicinal preparations, is known to cause skin cancer. The evidence assessed here indicates that arsenic can also cause liver, lung, kidney, and bladder cancer and that the population cancer risks due to arsenic in U.S. water supplies may be comparable to those from environmental tobacco smoke and radon in homes. Large population studies in an area of Taiwan with high arsenic levels in well water (170-800 micrograms/L) were used to establish dose-response relationships between cancer risks and the concentration of inorganic arsenic naturally present in water supplies. It was estimated that at the current EPA standard of 50 micrograms/L, the lifetime risk of dying from cancer of the liver, lung, kidney, or bladder from drinking 1 L/day of water could be as high as 13 per 1000 persons. It has been estimated that more than 350,000 people in the United States may be supplied with water containing more than 50 micrograms/L arsenic, and more than 2.5 million people may be supplied with water with levels above 25 micrograms/L. For average arsenic levels and water consumption patterns in the United States, the risk estimate was around 1/1000. Although further research is needed to validate these findings, measures to reduce arsenic levels in water supplies should be considered
Emergent global patterns of ecosystem structure and function from a mechanistic general ecosystem model
Anthropogenic activities are causing widespread degradation of ecosystems worldwide, threatening the ecosystem services upon which all human life depends. Improved understanding of this degradation is urgently needed to improve avoidance and mitigation measures. One tool to assist these efforts is predictive models of ecosystem structure and function that are mechanistic: based on fundamental ecological principles. Here we present the first mechanistic General Ecosystem Model (GEM) of ecosystem structure and function that is both global and applies in all terrestrial and marine environments. Functional forms and parameter values were derived from the theoretical and empirical literature where possible. Simulations of the fate of all organisms with body masses between 10 µg and 150,000 kg (a range of 14 orders of magnitude) across the globe led to emergent properties at individual (e.g., growth rate), community (e.g., biomass turnover rates), ecosystem (e.g., trophic pyramids), and macroecological scales (e.g., global patterns of trophic structure) that are in general agreement with current data and theory. These properties emerged from our encoding of the biology of, and interactions among, individual organisms without any direct constraints on the properties themselves. Our results indicate that ecologists have gathered sufficient information to begin to build realistic, global, and mechanistic models of ecosystems, capable of predicting a diverse range of ecosystem properties and their response to human pressures
Loop Interactions during Catalysis by Dihydrofolate Reductase fromMoritella profunda
Dihydrofolate reductase (DHFR) is often used as a model system to
study the relation between protein dynamics and catalysis. We have studied a
number of variants of the cold-adapted DHFR from Moritella profunda
(MpDHFR), in which the catalytically important M20 and FG loops have been
altered, and present a comparison with the corresponding variants of the wellstudied
DHFR from Escherichia coli (EcDHFR). Mutations in the M20 loop do not
affect the actual chemical step of transfer of hydride from reduced nicotinamide
adenine dinucleotide phosphate to the substrate 7,8-dihydrofolate in the catalytic
cycle in either enzyme; they affect the steady state turnover rate in EcDHFR but
not in MpDHFR. Mutations in the FG loop also have different effects on catalysis
by the two DHFRs. Despite the two enzymes most likely sharing a common catalytic cycle at pH 7, motions of these loops,
known to be important for progression through the catalytic cycle in EcDHFR, appear not to play a significant role in MpDHFR
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