10,804 research outputs found
A simple nearest-neighbor two-body Hamiltonian system for which the ground state is a universal resource for quantum computation
We present a simple quantum many-body system - a two-dimensional lattice of
qubits with a Hamiltonian composed of nearest-neighbor two-body interactions -
such that the ground state is a universal resource for quantum computation
using single-qubit measurements. This ground state approximates a cluster state
that is encoded into a larger number of physical qubits. The Hamiltonian we use
is motivated by the projected entangled pair states, which provide a
transparent mechanism to produce such approximate encoded cluster states on
square or other lattice structures (as well as a variety of other quantum
states) as the ground state. We show that the error in this approximation takes
the form of independent errors on bonds occurring with a fixed probability. The
energy gap of such a system, which in part determines its usefulness for
quantum computation, is shown to be independent of the size of the lattice. In
addition, we show that the scaling of this energy gap in terms of the coupling
constants of the Hamiltonian is directly determined by the lattice geometry. As
a result, the approximate encoded cluster state obtained on a hexagonal lattice
(a resource that is also universal for quantum computation) can be shown to
have a larger energy gap than one on a square lattice with an equivalent
Hamiltonian.Comment: 5 pages, 1 figure; v2 has a simplified lattice, an extended analysis
of errors, and some additional references; v3 published versio
Production of tau tau jj final states at the LHC and the TauSpinner algorithm: the spin-2 case
The TauSpinner algorithm is a tool that allows to modify the physics model of
the Monte Carlo generated samples due to the changed assumptions of event
production dynamics, but without the need of re-generating events. With the
help of weights -lepton production or decay processes can be modified
accordingly to a new physics model. In a recent paper a new version TauSpinner
ver.2.0.0 has been presented which includes a provision for introducing
non-standard states and couplings and study their effects in the
vector-boson-fusion processes by exploiting the spin correlations of
-lepton pair decay products in processes where final states include also
two hard jets. In the present paper we document how this can be achieved taking
as an example the non-standard spin-2 state that couples to Standard Model
particles and tree-level matrix elements with complete helicity information
included for the parton-parton scattering amplitudes into a -lepton pair
and two outgoing partons. This implementation is prepared as the external (user
provided) routine for the TauSpinner algorithm. It exploits amplitudes
generated by MadGraph5 and adopted to the TauSpinner algorithm format.
Consistency tests of the implemented matrix elements, reweighting algorithm and
numerical results for observables sensitive to polarization are
presented.Comment: 17 pages, 6 figures; version published in EPJ
Application of TauSpinner for studies on tau-lepton polarization and spin correlations in Z, W and H decays at LHC
The tau-lepton plays an important role in the physics program at LHC. Its
spin can be used for separation of signal from background or in measuring
properties of New Particles decaying to tau leptons.
The TauSpinner package represents a tool to modify tau spin effects in any
sample containing tau leptons. Generated events, featuring taus produced from
intermediate state W, Z, H bosons can be used as an input. The information on
the polarization and spin correlations is reconstructed from the kinematics of
the tau lepton(s) (nutau in case of W-mediated processes) and tau decay
products. By weights, attributed on the event-by-event basis, it enables
numerical evaluation and/or modification of the spin effects.
We review distributions to monitor spin effects in leptonic and hadronic tau
decays with up to three pions, to provide benchmarks for validation of spin
content of the event sample and to visualize the tau lepton spin polarization
and correlation effects. The demonstration examples for use of TauSpinner
libraries, are documented. New validation methods of such an approach are
provided. Other topics, like TauSpinner systematic errors or sensitivity of
experimental distributions to spin, are addressed in part only.
This approach is of interest for implementation of spin effects in embedded
tau lepton samples, where Z to mu mu events from data of muons are replaced by
simulated tau leptons. Embedding is used at LHC for estimating Z to tau tau
background to H to tau tau signatures.Comment: 1+41 pages, 5 figures in main text, multitude of figures in
appendice
A Contribution to the Examination of the Oral Mucosa Membrane Bioimpedance
U namjeri da ustanove osnovne vrijednosti bioimpedancije na zdravoj oralnoj sluznici autori su u 19 zdravih osoba uz pomoć posebno prilagođenoga mjernog uređaja mjerili vrijednosti modula i faznoga kuta bioimpedancije u deset referentnih točaka u usnoj šupljini. Mjerenje je izvršeno na deset frekvencija kvazilogaritamski rasprostranjenih u rasponu od 30 Hz do 1 MHz. Mjerenje je u svakoj
točki trajalo 30 sekundi.
Izmjerene vrijednosti pokazale su uočljive sličnosti distribucije rezultata za skupine mjernih točaka. Autori zaključuju da je dovoljno mjeriti na sluznici dorzuma jezika, nepca i obraza kao reprezentativnim područjima, a vrijednosti za ostala teže dostupna područja bitno se ne razlikuju od predloženih točaka. Također ja utvrđeno da se na visokim i niskim frakvencijama rezultati mjerenja
grupiraju te se predlaže da se raspon frekvencija suzi na 103 do 105 Hz.Asample of 19 healthy persons were tested by means of a specially adapted measuring device in order to obtain module values and bioimpedance phase angles in ten reference points distributed along the oral mucosa. The measurements were carried out at ten approximately logarithmic frequencies set out within the range of 30 Hz to 1 MHz. Each measurement lasted 30 seconds.
The results showed significant similarities on the group distribution of measuring points. This lead to the conclusion that the relevant measuring points were at lingual dorsum mucosa, hard palate and buccal mucosa, whereas the values for other less accessible regions did not significantly differ from the former. It was also found that
the measuring results were concentrated at low and high frequencies. Therefore, it is advisable to narrow down the
measuring range to 103 - 105 Hz
Production of \uptau τ lepton pairs with high p T jets at the LHC and the TauSpinner reweighting algorithm
The TauSpinner algorithm allows to modify the physics of the Monte Carlo
generated samples due to the changed assumptions of event production dynamics,
without re-generating events. To each event it attributes weights: the spin
effects of tau-lepton production or decay, or the production mechanism are
modified. There is no need to repeat the detector response simulation. We
document the extension to 2 to 4 processes in which the matrix elements for the
parton-parton scattering amplitudes into a tau-lepton pair and two outgoing
partons are used. Tree-level matrix elements for the Standard Model processes,
including the Higgs boson production are used. Automatically generated codes by
MadGraph5 have been adapted. Tests of the matrix elements, reweighting
algorithm and numerical results are presented. For averaged tau lepton
polarisation, we perform comparison of 2 to 2 and 2 to 4 matrix elements used
to calculate the spin weight in pp to tau tau j j events. We show, that for
events with tau-lepton pair close to the Z-boson peak, the tau-lepton
polarisation calculated using 2 to 4 matrix elements is very close to the one
calculated using 2 to 2 Born process only. For the m_(tautau) masses above the
Z-boson peak, the effect from including 2 to 4 matrix elements is also
marginal, however when restricting into subprocesses qq,q bar q to tau tau j j
only, it can lead to a 10% difference on the predicted tau-lepton polarisation.
Choice of electroweak scheme can have significant impact. The modification of
the electroweak or strong interaction can be performed with the re-weighting
technique. TauSpinner v.2.0.0, allows to introduce non-standard couplings for
the Higgs boson and study their effects in the vector-boson-fusion. The
discussion is relegated to forthcoming publications.Comment: 33 pages 7 figure
Leonardo's rule, self-similarity and wind-induced stresses in trees
Examining botanical trees, Leonardo da Vinci noted that the total
cross-section of branches is conserved across branching nodes. In this Letter,
it is proposed that this rule is a consequence of the tree skeleton having a
self-similar structure and the branch diameters being adjusted to resist
wind-induced loads
Effect of anisotropy on the ground-state magnetic ordering of the spin-one quantum -- model on the square lattice
We study the zero-temperature phase diagram of the
-- Heisenberg model for spin-1 particles on an
infinite square lattice interacting via nearest-neighbour () and
next-nearest-neighbour () bonds. Both bonds have the same -type
anisotropy in spin space. The effects on the quasiclassical N\'{e}el-ordered
and collinear stripe-ordered states of varying the anisotropy parameter
is investigated using the coupled cluster method carried out to high
orders. By contrast with the spin-1/2 case studied previously, we predict no
intermediate disordered phase between the N\'{e}el and collinear stripe phases,
for any value of the frustration , for either the -aligned () or -planar-aligned () states. The quantum phase
transition is determined to be first-order for all values of and
. The position of the phase boundary is determined
accurately. It is observed to deviate most from its classical position (for all values of ) at the Heisenberg isotropic point
(), where . By contrast, at the XY
isotropic point (), we find . In the
Ising limit () as expected.Comment: 20 pages, 5 figure
Polar catastrophe and electronic reconstructions at the LaAlO3/SrTiO3 interface: evidence from optical second harmonic generation
The so-called "polar catastrophe", a sudden electronic reconstruction taking
place to compensate for the interfacial ionic polar discontinuity, is currently
considered as a likely factor to explain the surprising conductivity of the
interface between the insulators LaAlO3 and SrTiO3. We applied optical second
harmonic generation, a technique that a priori can detect both mobile and
localized interfacial electrons, to investigating the electronic polar
reconstructions taking place at the interface. As the LaAlO3 film thickness is
increased, we identify two abrupt electronic rearrangements: the first takes
place at a thickness of 3 unit cells, in the insulating state; the second
occurs at a thickness of 4-6 unit cells, i.e., just above the threshold for
which the samples become conducting. Two possible physical scenarios behind
these observations are proposed. The first is based on an electronic transfer
into localized electronic states at the interface that acts as a precursor of
the conductivity onset. In the second scenario, the signal variations are
attributed to the strong ionic relaxations taking place in the LaAlO3 layer
Quantum Heisenberg antiferromagnet on low-dimensional frustrated lattices
Using a lattice-gas description of the low-energy degrees of freedom of the
quantum Heisenberg antiferromagnet on the frustrated two-leg ladder and bilayer
lattices we examine the magnetization process at low temperatures for these
spin models. In both cases the emergent discrete degrees of freedom implicate a
close relation of the frustrated quantum Heisenberg antiferromagnet to the
classical lattice gas with finite nearest-neighbor repulsion or, equivalently,
to the Ising antiferromagnet in a uniform magnetic field. Using this relation
we obtain analytical results for thermodynamically large systems in the
one-dimensional case. In the two-dimensional case we perform classical Monte
Carlo simulations for systems of up to sites.Comment: Submitted to Teoreticheskaya i Matematicheskaya Fizika (special issue
dedicated to the 90th anniversary of Professor Sergei Vladimirovich
Tyablikov
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