812 research outputs found
UK utility data integration: overcoming schematic heterogeneity
In this paper we discuss syntactic, semantic and schematic issues which inhibit the integration of utility data in the UK. We then focus on the techniques employed within the VISTA project to overcome schematic heterogeneity. A Global
Schema based architecture is employed. Although automated approaches to Global Schema definition were attempted
the heterogeneities of the sector were too great. A manual approach to Global Schema definition was employed. The
techniques used to define and subsequently map source utility data models to this schema are discussed in detail. In order to ensure a coherent integrated model, sub and cross domain validation issues are then highlighted. Finally the proposed framework and data flow for schematic integration is introduced
Security of the Bennett 1992 quantum-key distribution against individual attack over a realistic channel
The security of two-state quantum key distribution against individual attack
is estimated when the channel has losses and noises. We assume that Alice and
Bob use two nonorthogonal single-photon polarization states. To make our
analysis simple, we propose a modified B92 protocol in which Alice and Bob make
use of inconclusive results and Bob performs a kind of symmetrization of
received states. Using this protocol, Alice and Bob can estimate Eve's
information gain as a function of a few parameters which reflect the
imperfections of devices or Eve's disturbance. In some parameter regions, Eve's
maximum information gain shows counter-intuitive behavior, namely, it decreases
as the amount of disturbances increases. For a small noise rate Eve can extract
perfect information in the case where the angle between Alice's two states is
small or large, while she cannot extract perfect information for intermediate
angles. We also estimate the secret key gain which is the net growth of the
secret key per one pulse. We show the region where the modified B92 protocol
over a realistic channel is secure against individual attack.Comment: 16 pages, 15 figure
Efficient Computations of Encodings for Quantum Error Correction
We show how, given any set of generators of the stabilizer of a quantum code,
an efficient gate array that computes the codewords can be constructed. For an
n-qubit code whose stabilizer has d generators, the resulting gate array
consists of O(n d) operations, and converts k-qubit data (where k = n - d) into
n-qubit codewords.Comment: 16 pages, REVTeX, 3 figures within the tex
Achievable rates for the Gaussian quantum channel
We study the properties of quantum stabilizer codes that embed a
finite-dimensional protected code space in an infinite-dimensional Hilbert
space. The stabilizer group of such a code is associated with a symplectically
integral lattice in the phase space of 2N canonical variables. From the
existence of symplectically integral lattices with suitable properties, we
infer a lower bound on the quantum capacity of the Gaussian quantum channel
that matches the one-shot coherent information optimized over Gaussian input
states.Comment: 12 pages, 4 eps figures, REVTe
Entanglement required in achieving entanglement-assisted channel capacities
Entanglement shared between the two ends of a quantum communication channel
has been shown to be a useful resource in increasing both the quantum and
classical capacities for these channels. The entanglement-assisted capacities
were derived assuming an unlimited amount of shared entanglement per channel
use. In this paper, bounds are derived on the minimum amount of entanglement
required per use of a channel, in order to asymptotically achieve the capacity.
This is achieved by introducing a class of entanglement-assisted quantum codes.
Codes for classes of qubit channels are shown to achieve the quantum
entanglement-assisted channel capacity when an amount of shared entanglement
per channel given by, E = 1 - Q_E, is provided. It is also shown that for very
noisy channels, as the capacities become small, the amount of required
entanglement converges for the classical and quantum capacities.Comment: 9 pages, 2 figures, RevTex
On the distribution of entanglement changes produced by unitary operations
We consider the change of entanglement of formation produced by a
unitary transformation acting on a general (pure or mixed) state
describing a system of two qubits. We study numerically the probabilities of
obtaining different values of , assuming that the initial state is
randomly distributed in the space of all states according to the product
measure introduced by Zyczkowski {\it et al.} [Phys. Rev. A {\bf 58} (1998)
883]
Secure quantum key distribution using squeezed states
We prove the security of a quantum key distribution scheme based on
transmission of squeezed quantum states of a harmonic oscillator. Our proof
employs quantum error-correcting codes that encode a finite-dimensional quantum
system in the infinite-dimensional Hilbert space of an oscillator, and protect
against errors that shift the canonical variables p and q. If the noise in the
quantum channel is weak, squeezing signal states by 2.51 dB (a squeeze factor
e^r=1.34) is sufficient in principle to ensure the security of a protocol that
is suitably enhanced by classical error correction and privacy amplification.
Secure key distribution can be achieved over distances comparable to the
attenuation length of the quantum channel.Comment: 19 pages, 3 figures, RevTeX and epsf, new section on channel losse
A Two-Step Quantum Direct Communication Protocol Using Einstein-Podolsky-Rosen Pair Block
A protocol for quantum secure direct communication using blocks of EPR pairs
is proposed. A set of ordered EPR pairs is used as a data block for sending
secret message directly. The ordered EPR set is divided into two particle
sequences, a checking sequence and a message-coding sequence. After
transmitting the checking sequence, the two parties of communication check
eavesdropping by measuring a fraction of particles randomly chosen, with random
choice of two sets of measuring bases. After insuring the security of the
quantum channel, the sender, Alice encodes the secret message directly on the
message-coding sequence and send them to Bob. By combining the checking and
message-coding sequences together, Bob is able to read out the encoded messages
directly. The scheme is secure because an eavesdropper cannot get both
sequences simultaneously. We also discuss issues in a noisy channel.Comment: 8 pages and 2 figures. To appear in Phys Rev
Trace Complexity of Chaotic Reversible Cellular Automata
Delvenne, K\r{u}rka and Blondel have defined new notions of computational
complexity for arbitrary symbolic systems, and shown examples of effective
systems that are computationally universal in this sense. The notion is defined
in terms of the trace function of the system, and aims to capture its dynamics.
We present a Devaney-chaotic reversible cellular automaton that is universal in
their sense, answering a question that they explicitly left open. We also
discuss some implications and limitations of the construction.Comment: 12 pages + 1 page appendix, 4 figures. Accepted to Reversible
Computation 2014 (proceedings published by Springer
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