482 research outputs found
Continuous-variable quantum teleportation of entanglement
Entangled coherent states can be used to determine the entanglement fidelity
for a device that is designed to teleport coherent states. This entanglement
fidelity is universal, in that the calculation is independent of the use of
entangled coherent states and applies generally to the teleportation of
entanglement using coherent states. The average fidelity is shown to be a poor
indicator of the capability of teleporting entanglement; i.e., very high
average fidelity for the quantum teleportation apparatus can still result in
low entanglement fidelity for one mode of the two-mode entangled coherent
state.Comment: 5 pages, 1 figure, published versio
Requirements on collider data to match the precision of WMAP on supersymmetric dark matter
If future colliders discover supersymmetric particles and probe their
properties, one could predict the dark matter density of the Universe and would
constrain cosmology with the help of precision data provided by WMAP and
PLANCK.
We investigate how well the relic density can be predicted in minimal
supergravity (mSUGRA), with and without the assumption of mSUGRA when analysing
data. We determine the parameters to which the relic density is most sensitive,
and quantify the collider accuracy needed. Theoretical errors in the prediction
are investigated in some detail.Comment: 42 pages, 16 figures. v2 incorporates referee's comments: minor
corrections/clarifications with additional figures to show regions of m12-m0
plane considere
Multipartite entangled coherent states
We propose a scheme for generating multipartite entangled coherent states via
entanglement swapping, with an example of a physical realization in ion traps.
Bipartite entanglement of these multipartite states is quantified by the
concurrence. We also use the --tangle to compute multipartite entanglement
for certain systems. Finally we establish that these results for entanglement
can be applied to more general multipartite entangled nonorthogonal states.Comment: 7 pages, two figures. We added more detail discussions on the
generation of multipartite entangled coherent states and multipartite
entangelemen
Perspectives for the detection and measurement of Supersymmetry in the focus point region of mSUGRA models with the ATLAS detector at LHC
This paper discusses the ATLAS potential to study Supersymmetry for the
"Focus-Point" region of the parameter space of mSUGRA models. The potential to
discovery a deviation from Standard Model expectations with the first few
of LHC data was studied using the parametrized simulation of the
ATLAS detector. Several signatures were considered, involving hard jets, large
missing energy, and either -tagged jets, opposite-sign isolated electron or
muon pairs, or top quarks reconstructed exploiting their fully hadronic decays.
With only 1 of data each of these signatures may allow to observe
an excess of events over Standard Model expectation with a statistical
significance exceeding 5 standard deviations. An analytical expression was
derived for the shape of the distribution of the dilepton invariant mass
arising from the three-body leptonic decay of the neutralinos under the
hypothesis of heavy scalars, which is appropriate for the focus-point scenario.
The resulting function was used to fit the distribution of the dilepton
invariant mass obtained with simulated LHC data, and to extract the value of
two kinematic endpoints measuring the and
the mass differences. This information was
used to constrain the MSSM parameter space compatible with the data
Naturalness Priors and Fits to the Constrained Minimal Supersymmetric Standard Model
We examine the effect of a prior that favours low values of fine-tuning on
Bayesian multi-dimensional fits of the constrained minimal supersymmetric
standard model (CMSSM or mSUGRA) to current data. The dark matter relic
density, the anomalous magnetic moment of the muon and the branching ratio of
b->s gamma are all used to constrain the model via a Markov Chain Monte Carlo
sampler. As a result of the naturalness prior, posterior probability
distributions skew towards lighter higgs and sparticle masses, the effect being
most pronounced in the gaugino sector. Interestingly, slepton masses are an
exception and skew towards heavier masses. The lightest CP-even Higgs h^0-pole
region becomes allowed at the 2 sigma level for the latest combination of
measurements of m_t=172.7+/-2.9 GeV, provided we allow for a theoretical error
in the prediction of its mass m_{h^0}. m_{h^0} is constrained to be less than
120 GeV at the 95% C.L. Probing the branching ratio of B_s->mu^+ mu^- to the
level of 2 x 10^{-8}, as might be achieved by the Tevatron experiments, would
cover 32% of the probability density, irrespective of which of the two priors
is used.Comment: 15 pages, 5 figures. Ref adde
Entanglement in bipartite generalized coherent states
Entanglement in a class of bipartite generalized coherent states is
discussed. It is shown that a positive parameter can be associated with the
bipartite generalized coherent states so that the states with equal value for
the parameter are of equal entanglement. It is shown that the maximum possible
entanglement of 1 bit is attained if the positive parameter equals .
The result that the entanglement is one bit when the relative phase between the
composing states is in bipartite coherent states is shown to be true for
the class of bipartite generalized coherent states considered.Comment: 10 pages, 4 figures; typos corrected and figures redrawn for better
clarit
Constraining Dark Matter in the MSSM at the LHC
In the event that R-Parity conserving supersymmetry (SUSY) is discovered at
the LHC, a key issue which will need to be addressed will be the consistency of
that signal with astrophysical and non-accelerator constraints on SUSY Dark
Matter. This issue is studied for the SPA benchmark model based on measurements
of end-points and thresholds in the invariant mass spectra of various
combinations of leptons and jets. These measurements are used to constrain the
soft SUSY breaking parameters at the electroweak scale in a general MSSM model.
Based on these constraints, we assess the accuracy with which the Dark Matter
relic density can be measured.Comment: 21 pages, 12 figure
Atmospheric Channel Characteristics for Quantum Communication with Continuous Polarization Variables
We investigate the properties of an atmospheric channel for free space
quantum communication with continuous polarization variables. In our
prepare-and-measure setup, coherent polarization states are transmitted through
an atmospheric quantum channel of 100m length on the roof of our institute's
building. The signal states are measured by homodyne detection with the help of
a local oscillator (LO) which propagates in the same spatial mode as the
signal, orthogonally polarized to it. Thus the interference of signal and LO is
excellent and atmospheric fluctuations are autocompensated. The LO also acts as
spatial and spectral filter, which allows for unrestrained daylight operation.
Important characteristics for our system are atmospheric channel influences
that could cause polarization, intensity and position excess noise. Therefore
we study these influences in detail. Our results indicate that the channel is
suitable for our quantum communication system in most weather conditions.Comment: 6 pages, 4 figures, submitted to Applied Physics B following an
invitation for the special issue "Selected Papers Presented at the 2009
Spring Meeting of the Quantum Optics and Photonics Section of the German
Physical Society
Tailoring Single and Multiphoton Probabilities of a Single Photon On-Demand Source
As typically implemented, single photon sources cannot be made to produce
single photons with high probability, while simultaneously suppressing the
probability of yielding two or more photons. Because of this, single photon
sources cannot really produce single photons on demand. We describe a
multiplexed system that allows the probabilities of producing one and more
photons to be adjusted independently, enabling a much better approximation of a
source of single photons on demand.Comment: 4 pages, LaTex, 2 figures, twocolumn and RevTex Style for PR
Phenomenology of a Fluxed MSSM
We analyze the phenomenology of a set of minimal supersymmetric standard
model (MSSM) soft terms inspired by flux-induced supersymmetry (SUSY)-breaking
in Type IIB string orientifolds. The scheme is extremely constrained with
essentially only two free mass parameters: a parameter M, which sets the scale
of soft terms, and the mu parameter. After imposing consistent radiative
electro-weak symmetry breaking (EWSB) the model depends upon one mass parameter
(say, M). In spite of being so constrained one finds consistency with EWSB
conditions. We demonstrate that those conditions have two solutions for mu<0,
and none for mu>0. The parameter tan beta results as a prediction and is
approximately 3-5 for one solution, and 25-40 for the other, depending upon M
and the top mass. We examine further constraints on the model coming from b->s
gamma, the muon g-2, Higgs mass limits and WMAP constraints on dark matter. The
MSSM spectrum is predicted in terms of the single free parameter M. The low tan
beta branch is consistent with a relatively light spectrum although it is
compatible with standard cosmology only if the lightest neutralino is unstable.
The high tan beta branch is compatible with all phenomenological constraints,
but has quite a heavy spectrum. We argue that the fine-tuning associated to
this heavy spectrum would be substantially ameliorated if an additional
relationship mu=-2M were present in the underlying theory.Comment: 18 pages, minor revision
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