377 research outputs found
Generalized Flow and Determinism in Measurement-based Quantum Computation
We extend the notion of quantum information flow defined by Danos and Kashefi
for the one-way model and present a necessary and sufficient condition for the
deterministic computation in this model. The generalized flow also applied in
the extended model with measurements in the X-Y, X-Z and Y-Z planes. We apply
both measurement calculus and the stabiliser formalism to derive our main
theorem which for the first time gives a full characterization of the
deterministic computation in the one-way model. We present several examples to
show how our result improves over the traditional notion of flow, such as
geometries (entanglement graph with input and output) with no flow but having
generalized flow and we discuss how they lead to an optimal implementation of
the unitaries. More importantly one can also obtain a better quantum
computation depth with the generalized flow rather than with flow. We believe
our characterization result is particularly essential for the study of the
algorithms and complexity in the one-way model.Comment: 16 pages, 10 figure
Generalized Flow and Determinism in Measurement-based Quantum Computation
We extend the notion of quantum information flow defined by Danos and Kashefi
for the one-way model and present a necessary and sufficient condition for the
deterministic computation in this model. The generalized flow also applied in
the extended model with measurements in the X-Y, X-Z and Y-Z planes. We apply
both measurement calculus and the stabiliser formalism to derive our main
theorem which for the first time gives a full characterization of the
deterministic computation in the one-way model. We present several examples to
show how our result improves over the traditional notion of flow, such as
geometries (entanglement graph with input and output) with no flow but having
generalized flow and we discuss how they lead to an optimal implementation of
the unitaries. More importantly one can also obtain a better quantum
computation depth with the generalized flow rather than with flow. We believe
our characterization result is particularly essential for the study of the
algorithms and complexity in the one-way model.Comment: 16 pages, 10 figure
Phase distortions of attosecond pulses produced by resonance-enhanced high harmonic generation
Resonant enhancement of high harmonic generation can be obtained in plasmas
containing ions with strong radiative transitions resonant with harmonic
orders. The mechanism for this enhancement is still debated. We perform the
first temporal characterization of the attosecond emission from a tin plasma
under near-resonant conditions for two different resonance detunings. We show
that the resonance considerably changes the relative phase of neighbouring
harmonics. For very small detunings, their phase locking may even be lost,
evidencing strong phase distortions in the emission process and a modified
attosecond structure. These features are well reproduced by our simulations,
allowing their interpretation in terms of the phase of the recombination dipole
moment
A relational quantum computer using only two-qubit total spin measurement and an initial supply of highly mixed single qubit states
We prove that universal quantum computation is possible using only (i) the
physically natural measurement on two qubits which distinguishes the singlet
from the triplet subspace, and (ii) qubits prepared in almost any three
different (potentially highly mixed) states. In some sense this measurement is
a `more universal' dynamical element than a universal 2-qubit unitary gate,
since the latter must be supplemented by measurement. Because of the rotational
invariance of the measurement used, our scheme is robust to collective
decoherence in a manner very different to previous proposals - in effect it is
only ever sensitive to the relational properties of the qubits.Comment: TR apologises for yet again finding a coauthor with a ridiculous
middle name [12
Quantum picturalism for topological cluster-state computing
Topological quantum computing is a way of allowing precise quantum
computations to run on noisy and imperfect hardware. One implementation uses
surface codes created by forming defects in a highly-entangled cluster state.
Such a method of computing is a leading candidate for large-scale quantum
computing. However, there has been a lack of sufficiently powerful high-level
languages to describe computing in this form without resorting to single-qubit
operations, which quickly become prohibitively complex as the system size
increases. In this paper we apply the category-theoretic work of Abramsky and
Coecke to the topological cluster-state model of quantum computing to give a
high-level graphical language that enables direct translation between quantum
processes and physical patterns of measurement in a computer - a "compiler
language". We give the equivalence between the graphical and topological
information flows, and show the applicable rewrite algebra for this computing
model. We show that this gives us a native graphical language for the design
and analysis of topological quantum algorithms, and finish by discussing the
possibilities for automating this process on a large scale.Comment: 18 pages, 21 figures. Published in New J. Phys. special issue on
topological quantum computin
Métodos electroquímicos semicuantitativos de estudio de lo corrosión por picaduras del acero para armaduras de hormigón
El acero embebido en el hormigón se encuentra sometido a un medio de elevada alcalinidad (pH comprendido entre 12 y 13), debido a la cal libre, a los álcalis que contiene el cemento, y al Ca(0H)2 que se forma durante la hidratación de los silicatos. En esta situación, el acero se halla recubierto por una capa de óxidos e hidróxidos estables que lo mantienen pasivado, interponiendo una barrera entre él y los agentes agresivos
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