12,329 research outputs found
Optimal purification of thermal graph states
In this paper, a purification protocol is presented and its performance is
proven to be optimal when applied to a particular subset of graph states that
are subject to local Z-noise. Such mixed states can be produced by bringing a
system into thermal equilibrium, when it is described by a Hamiltonian which
has a particular graph state as its unique ground state. From this protocol, we
derive the exact value of the critical temperature above which purification is
impossible, as well as the related optimal purification rates. A possible
simulation of graph Hamiltonians is proposed, which requires only bipartite
interactions and local magnetic fields, enabling the tuning of the system
temperature.Comment: 5 pages, 4 figures v2: published versio
Prevalence of sulfonamide resistance genes in bacterial isolates from manured agricultural soils and pig slurry in the United Kingdom
Prevalence of three sulfonamide resistance genes, sul1, sul2 and sul3 and sulfachloropyridazine (SCP) resistance was determined in bacteria isolated from UK manured agricultural clay soils and slurry samples, over a two year period. Slurry from tylosin-fed pigs amended with SCP and oxytetracycline (OTC) was used for manuring. Sul gene positive isolates were further screened for the presence of class 1 and 2 integrons. Phenotypic resistance to SCP was significantly higher in pig slurry and post application soil than in pre-application soil. Of 5isolates, 23 % carried sul1, 18 % sul2 and 9 % sul3 only. Two percent of isolates contained all three sul genes. Class 1 and class 2 integrons were identified in 5 % and 11.7 % of sul positive isolates. In previous reports, sul1 was linked to class 1 integrons, but in this study only 8 % of sul1 positive isolates carried the intI1 gene. Sulfonamide resistant pathogens were identified in slurry amended soil and soil leachate, including Shigella flexneri, Aerococcus spp. and Acinetobacter baumanni, suggesting a potential environmental reservoir. Sulfonamide resistance in Psychrobacter, Enterococcus and Bacillus spp. is reported for the first time, and this study also provides the first description of the genotype sul1, sul2 and sul3 outside the Enterobacteriacae, and in the soil environment
Integron prevalence and diversity in manured soil
Integron abundance and diversity were studied in soil amended with pig slurry. Real-time PCR illustrated a significant increase in class 1 integron prevalence post slurry-application with increased prevalence still evident at 10 months post-application. Culture dependent data revealed 10 genera, including putative human pathogens, carrying class 1 and 2 integrons
Functional renormalization group at large N for random manifolds
We introduce a method, based on an exact calculation of the effective action
at large N, to bridge the gap between mean field theory and renormalization in
complex systems. We apply it to a d-dimensional manifold in a random potential
for large embedding space dimension N. This yields a functional renormalization
group equation valid for any d, which contains both the O(epsilon=4-d) results
of Balents-Fisher and some of the non-trivial results of the Mezard-Parisi
solution thus shedding light on both. Corrections are computed at order O(1/N).
Applications to the problems of KPZ, random field and mode coupling in glasses
are mentioned
Driven particle in a random landscape: disorder correlator, avalanche distribution and extreme value statistics of records
We review how the renormalized force correlator Delta(u), the function
computed in the functional RG field theory, can be measured directly in
numerics and experiments on the dynamics of elastic manifolds in presence of
pinning disorder. We show how this function can be computed analytically for a
particle dragged through a 1-dimensional random-force landscape. The limit of
small velocity allows to access the critical behavior at the depinning
transition. For uncorrelated forces one finds three universality classes,
corresponding to the three extreme value statistics, Gumbel, Weibull, and
Frechet. For each class we obtain analytically the universal function Delta(u),
the corrections to the critical force, and the joint probability distribution
of avalanche sizes s and waiting times w. We find P(s)=P(w) for all three
cases. All results are checked numerically. For a Brownian force landscape,
known as the ABBM model, avalanche distributions and Delta(u) can be computed
for any velocity. For 2-dimensional disorder, we perform large-scale numerical
simulations to calculate the renormalized force correlator tensor
Delta_{ij}(u), and to extract the anisotropic scaling exponents zeta_x >
zeta_y. We also show how the Middleton theorem is violated. Our results are
relevant for the record statistics of random sequences with linear trends, as
encountered e.g. in some models of global warming. We give the joint
distribution of the time s between two successive records and their difference
in value w.Comment: 41 pages, 35 figure
A Magnetic Resonance Realization of Decoherence-Free Quantum Computation
We report the realization, using nuclear magnetic resonance techniques, of
the first quantum computer that reliably executes an algorithm in the presence
of strong decoherence. The computer is based on a quantum error avoidance code
that protects against a class of multiple-qubit errors. The code stores two
decoherence-free logical qubits in four noisy physical qubits. The computer
successfully executes Grover's search algorithm in the presence of arbitrarily
strong engineered decoherence. A control computer with no decoherence
protection consistently fails under the same conditions.Comment: 5 pages with 3 figures, revtex4, accepted by Physical Review Letters;
v2 minor revisions to conten
Quantum computation in optical lattices via global laser addressing
A scheme for globally addressing a quantum computer is presented along with
its realisation in an optical lattice setup of one, two or three dimensions.
The required resources are mainly those necessary for performing quantum
simulations of spin systems with optical lattices, circumventing the necessity
for single qubit addressing. We present the control procedures, in terms of
laser manipulations, required to realise universal quantum computation. Error
avoidance with the help of the quantum Zeno effect is presented and a scheme
for globally addressed error correction is given. The latter does not require
measurements during the computation, facilitating its experimental
implementation. As an illustrative example, the pulse sequence for the
factorisation of the number fifteen is given.Comment: 11 pages, 10 figures, REVTEX. Initialisation and measurement
procedures are adde
A Note on Anatomical Changes of White Oak Wood Upon Exposure to Gamma Radiation
White oak heartwood samples were exposed to 650, 950 and 1900 MRad of cobalt-60 gamma radiation. The holocellulose portion of the heartwood cell walls was degraded while the lignin percentage remained relatively unchanged. Tangential vessel diameter, ray cell length, and length and width of intervessel pits increased upon exposure while tangential vessel-wall thickness, ray cell double-wall thickness, and latewood fiber double-wall thickness decreased
Super-rough phase of the random-phase sine-Gordon model: Two-loop results
We consider the two-dimensional random-phase sine-Gordon and study the
vicinity of its glass transition temperature , in an expansion in small
, where denotes the temperature. We derive
renormalization group equations in cubic order in the anharmonicity, and show
that they contain two universal invariants. Using them we obtain that the
correlation function in the super-rough phase for temperature behaves
at large distances as , where the amplitude
is a universal function of temperature
. This result differs at
two-loop order, i.e., , from the prediction based on
results from the "nearly conformal" field theory of a related fermion model. We
also obtain the correction-to-scaling exponent.Comment: 34 page
- …