291 research outputs found
Pattern recognition on a quantum computer
By means of a simple example it is demonstrated that the task of finding and
identifying certain patterns in an otherwise (macroscopically) unstructured
picture (data set) can be accomplished efficiently by a quantum computer.
Employing the powerful tool of the quantum Fourier transform the proposed
quantum algorithm exhibits an exponential speed-up in comparison with its
classical counterpart. The digital representation also results in a
significantly higher accuracy than the method of optical filtering. PACS:
03.67.Lx, 03.67.-a, 42.30.Sy, 89.70.+c.Comment: 6 pages RevTeX, 1 figure, several correction
Improved Bounds on Quantum Learning Algorithms
In this article we give several new results on the complexity of algorithms
that learn Boolean functions from quantum queries and quantum examples.
Hunziker et al. conjectured that for any class C of Boolean functions, the
number of quantum black-box queries which are required to exactly identify an
unknown function from C is ,
where is a combinatorial parameter of the class C. We
essentially resolve this conjecture in the affirmative by giving a quantum
algorithm that, for any class C, identifies any unknown function from C using
quantum black-box
queries.
We consider a range of natural problems intermediate between the exact
learning problem (in which the learner must obtain all bits of information
about the black-box function) and the usual problem of computing a predicate
(in which the learner must obtain only one bit of information about the
black-box function). We give positive and negative results on when the quantum
and classical query complexities of these intermediate problems are
polynomially related to each other.
Finally, we improve the known lower bounds on the number of quantum examples
(as opposed to quantum black-box queries) required for -PAC
learning any concept class of Vapnik-Chervonenkis dimension d over the domain
from to . This new lower bound comes
closer to matching known upper bounds for classical PAC learning.Comment: Minor corrections. 18 pages. To appear in Quantum Information
Processing. Requires: algorithm.sty, algorithmic.sty to buil
Precision calculation of the pi^- deuteron scattering length and its impact on threshold pi-N scattering
We present a calculation of the pi^- d scattering length with an accuracy of
a few percent using chiral perturbation theory. For the first time
isospin-violating corrections are included consistently. Using data on pionic
deuterium and pionic hydrogen atoms, we extract the isoscalar and isovector
pion-nucleon scattering lengths and obtain a^+=(7.6 +/- 3.1) x 10^{-3} mpi^{-1}
and a^-=(86.1 +/- 0.9) x 10^{-3} mpi^{-1}. Via the Goldberger-Miyazawa-Oehme
sum rule, this leads to a charged-pion-nucleon coupling constant g_c^2/4 pi =
13.69 +/- 0.20.Comment: 6 pages, 2 figures. Discussion of several points expanded, references
added in this version, which will appear in Physics Letters
The modelery: a collaborative web based repository
Software development processes are known to produce a large set of artifacts such as models, code and documentation. Keeping track of these artifacts without supporting tools is not easy, and making them available to others can be even harder. Standard version control systems are not able to solve this issue. More than keeping track of versions, a system to help organize and make artifacts available in meaningful ways is needed. In this paper we review a number of alternative systems, and present the requirements and the implementation of a collaborative web repository which we developed to solve this issue.Project LATiCES: Languages And Tools for Critical rEal-time Systems (Ref. NORTE-07-0124-FEDER-000062)
is financed by the North Portugal Regional Operational Programme (ON.2 - O Novo Norte), under the National Strategic Reference Framework (NSRF), through the European Regional Development Fund (ERDF), and by national funds, through the Portuguese funding agency, FundacĂŁo para a CiĂȘncia e a Tecnologia (FCT)
Precision calculation of threshold pi^- d scattering, pi N scattering lengths, and the GMO sum rule
We use chiral perturbation theory (ChPT) to calculate the
scattering length with an accuracy of a few percent, including
isospin-violating corrections both in the two- and three-body sector. In
particular, we provide the technical details of a recent letter, where we used
data on pionic deuterium and pionic hydrogen atoms to extract the isoscalar and
isovector pion-nucleon scattering lengths and . We study
isospin-breaking contributions to the three-body part of due to
mass differences, isospin violation in the scattering lengths, and
virtual photons. This last class of effects is ostensibly infrared enhanced due
to the smallness of the deuteron binding energy. However, we show that the
leading virtual-photon effects that might undergo such enhancement cancel, and
hence the standard ChPT counting provides a reliable estimate of isospin
violation in due to virtual photons. Finally, we discuss the
validity of the Goldberger-Miyazawa-Oehme sum rule in the presence of isospin
violation, and use it to determine the charged-pion-nucleon coupling constant.Comment: 46 pages, 7 figures. Discussion of several points expanded,
references added, version published in Nuclear Physics
The âmosaic habitatâ concept in human evolution: past and present
The habitats preferred by hominins and other species are an important theme in palaeoanthropology, and the âmosaic habitatâ (also referred to as habitat heterogeneity) has been a central concept in this regard for the last four decades. Here we explore the development of this concept â loosely defined as a range of different habitat types, such as woodlands, riverine forest and savannah within a limited spatial areaâ in studies of human evolution in the last sixty years or so. We outline the key developments that took place before and around the time when the term âmosaicâ came to wider palaeoanthropological attention. To achieve this we used an analysis of the published literature, a study of illustrations of hominin evolution from 1925 onwards and an email survey of senior researchers in palaeoanthropology and related fields. We found that the term mosaic starts to be applied in palaeoanthropological thinking during the 1970âs due to the work of a number of researchers, including Karl Butzer and Glynn Isaac , with the earliest usage we have found of âmosaicâ in specific reference to hominin habitats being by Adriaan Kortlandt (1972). While we observe a steady increase in the numbers of publications reporting mosaic palaeohabitats, in keeping with the growing interest and specialisation in various methods of palaeoenvironmental reconstruction, we also note that there is a lack of critical studies that define this habitat, or examine the temporal and spatial scales associated with it. The general consensus within the field is that the concept now requires more detailed definition and study to evaluate its role in human evolution
Measurement of the cross section of high transverse momentum ZâbbÌ production in protonâproton collisions at âs = 8 TeV with the ATLAS detector
This Letter reports the observation of a high transverse momentum ZâbbÌ signal in protonâproton collisions at âs=8 TeV and the measurement of its production cross section. The data analysed were collected in 2012 with the ATLAS detector at the LHC and correspond to an integrated luminosity of 19.5 fbâÂč. The ZâbbÌ decay is reconstructed from a pair of b -tagged jets, clustered with the anti-ktkt jet algorithm with R=0.4R=0.4, that have low angular separation and form a dijet with pT>200 GeVpT>200 GeV. The signal yield is extracted from a fit to the dijet invariant mass distribution, with the dominant, multi-jet background mass shape estimated by employing a fully data-driven technique that reduces the dependence of the analysis on simulation. The fiducial cross section is determined to be
ÏZâbbÂŻfid=2.02±0.20 (stat.) ±0.25 (syst.)±0.06 (lumi.) pb=2.02±0.33 pb,
in good agreement with next-to-leading-order theoretical predictions
- âŠ