391 research outputs found
Enhancement of Entanglement Percolation in Quantum Networks via Lattice Transformations
We study strategies for establishing long-distance entanglement in quantum
networks. Specifically, we consider networks consisting of regular lattices of
nodes, in which the nearest neighbors share a pure, but non-maximally entangled
pair of qubits. We look for strategies that use local operations and classical
communication. We compare the classical entanglement percolation protocol, in
which every network connection is converted with a certain probability to a
singlet, with protocols in which classical entanglement percolation is preceded
by measurements designed to transform the lattice structure in a way that
enhances entanglement percolation. We analyze five examples of such comparisons
between protocols and point out certain rules and regularities in their
performance as a function of degree of entanglement and choice of operations.Comment: 12 pages, 17 figures, revtex4. changes from v3: minor stylistic
changes for journal reviewer, minor changes to figures for journal edito
Risk factors for vulnerable youth in urban townships in South Africa: the potential contribution of reactive attachment disorder
Reactive attachment disorder (RAD) is a psychiatric disorder developing in early or middle childhood as a consequence of significant failures in the caregiving environment. RAD results in children failing to relate socially, either by exhibiting markedly inhibited behaviour or by indiscriminate social behaviour and is associated with significant socio-behavioural problems in the longer term. This study examined RAD in South Africa, a setting with high environmental risks.
We recruited a sub-sample of 40 10-year-old children from a cohort enrolled during pregnancy for whom early attachment status was known. Children were purposefully selected to represent the four attachment categories using the data available on the strange situation procedure (SSP) at 18 months. The Manchester Child Attachment Story Task (MCAST) assessed current attachment and RAD was diagnosed using a standardised assessment package. A high proportion of the children (5/40% or 12.5%) fulfilled diagnostic criteria for RAD; all were boys and were displaying the disinhibited type. SSP classification at 18 months was not significantly associated with RAD symptoms at age of 10 years, while current MCAST classifications were. This suggests that children in this sample are at much higher risk of RAD than in high-income populations, and despite a fairly typical attachment distribution in this population at 18 months, RAD was evidenced in later childhood and associated with current attachment disorganisation.
The strengths of this research include its longitudinal nature and use of diagnostic assessments. Given increasing evidence that RAD is relatively stable over time and introduces longer term socio-behavioural risks; the high rate of RAD in this sample (12.5%) highlights potential developmental threats to children in low- and middle-income countries (LMICs). Our results should be interpreted with caution given sample size and risk of selection bias. Further research is needed to confirm these findings
Preparation of Knill-Laflamme-Milburn states using tunable controlled phase gate
A specific class of partially entangled states known as
Knill-Laflamme-Milburn states (or KLM states) has been proved to be useful in
relation to quantum information processing [Knill et al., Nature 409, 46
(2001)]. Although the usage of such states is widely investigated, considerably
less effort has been invested into experimentally accessible preparation
schemes. This paper discusses the possibility to employ a tunable controlled
phase gate to generate an arbitrary Knill-Laflamme-Milburn state. In the first
part, the idea of using the controlled phase gate is explained on the case of
two-qubit KLM states. Optimization of the proposed scheme is then discussed for
the framework of linear optics. Subsequent generalization of the scheme to
arbitrary n-qubit KLM state is derived in the second part of this paper.Comment: 5 pages, 4 figures, accepted in Journal of Physics
Schedule for Affective Disorders and Schizophrenia for School-Age Children - Present and Lifetime Version (K-SADS-PL), DSM-5 update: translation into Brazilian Portuguese
Brazilian governmental research funding agency Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Brazilian governmental research funding agency Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)Brazilian governmental research funding agency Fundacao de Amparo a Pesquisa do Estado do Rio Grande do Sul (FAPERGS)ShireNovartisEli LillyJanssen-CilagUniv Fed Rio Grande do Sul, Fac Med, Dept Psiquiatria, Porto Alegre, RS, BrazilUniv Fed Rio Grande do Sul, Fac Med, Dept Pediat, Porto Alegre, RS, BrazilUniv Sao Paulo, Fac Med, Dept & Inst Psiquiatria, Sao Paulo, SP, BrazilUniv Fed Sao Paulo, Fac Med, Dept & Inst Psiquiatria, Sao Paulo, SP, BrazilPontifica Univ Catolica Rio Grande do Sul, Dev Cognit Neurosci Res Grp GNCD, Porto Alegre, RS, BrazilInst Bairral Psiquiatria, Ctr Integrado Desenvolvimento Infancia & Adolesce, Itapira, BrazilUniv Fed Sao Paulo, Fac Med, Dept & Inst Psiquiatria, Sao Paulo, SP, BrazilWeb of Scienc
Brokered Graph State Quantum Computing
We describe a procedure for graph state quantum computing that is tailored to
fully exploit the physics of optically active multi-level systems. Leveraging
ideas from the literature on distributed computation together with the recent
work on probabilistic cluster state synthesis, our model assigns to each
physical system two logical qubits: the broker and the client. Groups of
brokers negotiate new graph state fragments via a probabilistic optical
protocol. Completed fragments are mapped from broker to clients via a simple
state transition and measurement. The clients, whose role is to store the
nascent graph state long term, remain entirely insulated from failures during
the brokerage. We describe an implementation in terms of NV-centres in diamond,
where brokers and clients are very naturally embodied as electron and nuclear
spins.Comment: 5 pages, 3 figure
Cluster state preparation using gates operating at arbitrary success probabilities
Several physical architectures allow for measurement-based quantum computing
using sequential preparation of cluster states by means of probabilistic
quantum gates. In such an approach, the order in which partial resources are
combined to form the final cluster state turns out to be crucially important.
We determine the influence of this classical decision process on the expected
size of the final cluster. Extending earlier work, we consider different
quantum gates operating at various probabilites of success. For finite
resources, we employ a computer algebra system to obtain the provably optimal
classical control strategy and derive symbolic results for the expected final
size of the cluster. We identify two regimes: When the success probability of
the elementary gates is high, the influence of the classical control strategy
is found to be negligible. In that case, other figures of merit become more
relevant. In contrast, for small probabilities of success, the choice of an
appropriate strategy is crucial.Comment: 7 pages, 9 figures, contribution to special issue of New J. Phys. on
"Measurement-Based Quantum Information Processing". Replaced with published
versio
The efficiencies of generating cluster states with weak non-linearities
We propose a scalable approach to building cluster states of matter qubits
using coherent states of light. Recent work on the subject relies on the use of
single photonic qubits in the measurement process. These schemes can be made
robust to detector loss, spontaneous emission and cavity mismatching but as a
consequence the overhead costs grow rapidly, in particular when considering
single photon loss. In contrast, our approach uses continuous variables and
highly efficient homodyne measurements. We present a two-qubit scheme, with a
simple bucket measurement system yielding an entangling operation with success
probability 1/2. Then we extend this to a three-qubit interaction, increasing
this probability to 3/4. We discuss the important issues of the overhead cost
and the time scaling. This leads to a "no-measurement" approach to building
cluster states, making use of geometric phases in phase space.Comment: 21 pages, to appear in special issue of New J. Phys. on
"Measurement-Based Quantum Information Processing
Integration of highly probabilistic sources into optical quantum architectures: perpetual quantum computation
In this paper we introduce a design for an optical topological cluster state
computer constructed exclusively from a single quantum component. Unlike
previous efforts we eliminate the need for on demand, high fidelity photon
sources and detectors and replace them with the same device utilised to create
photon/photon entanglement. This introduces highly probabilistic elements into
the optical architecture while maintaining complete specificity of the
structure and operation for a large scale computer. Photons in this system are
continually recycled back into the preparation network, allowing for a
arbitrarily deep 3D cluster to be prepared using a comparatively small number
of photonic qubits and consequently the elimination of high frequency,
deterministic photon sources.Comment: 19 pages, 13 Figs (2 Appendices with additional Figs.). Comments
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