20,065 research outputs found
Characterization of classical Gaussian processes using quantum probes
We address the use of a single qubit as a quantum probe to characterize the
properties of classical noise. In particular, we focus on the characterization
of classical noise arising from the interaction with a stochastic field
described by Gaussian processes. The tools of quantum estimation theory allow
us to find the optimal state preparation for the probe, the optimal interaction
time with the external noise, and the optimal measurement to effectively
extract information on the noise parameter. We also perform a set of simulated
experiments to assess the performances of maximum likelihood estimator, showing
that the asymptotic regime, where the estimator is unbiased and efficient, is
approximately achieved after few thousands repeated measurements on the probe
system.Comment: 7 pages, 4 figures, to appear in Phys. Lett.
Public perceptions of the favelas in Rio de Janeiro: a post World Cup 2014 and pre 2016 Olympics Assessment
This research assesses public perception of the favelas of Rio de Janeiro following the awarding of the bids for both the 2014 World Cup and 2016 Olympics. In preparation of these mega sports events, Rio has been challenged to improve infrastructure, build Olympic venues and reduce crime in the favelas. The purpose of the research is to collect data on the perceptions of potential visitors to Brazil, specifically, Rio de Janeiro to determine if the preparation for and hosting of the mega sports events is changing the image of the favelas
Selective Serotonin Reuptake Inhibitors and Cosmetic Psychopharmacology: Ethical and Deontological Dilemmas
Measuring the growth rate of structure with Type IA Supernovae from LSST
We investigate measuring the peculiar motions of galaxies up to using
Type Ia supernovae (SNe Ia) from LSST, and predict the subsequent constraints
on the growth rate of structure. We consider two cases. Our first is based on
measurements of the volumetric SNe Ia rate and assumes we can obtain
spectroscopic redshifts and light curves for varying fractions of objects that
are detected pre-peak luminosity by LSST (some of which may be obtained by LSST
itself and others which would require additional follow-up). We find that these
measurements could produce growth rate constraints at that
significantly outperform those using Redshift Space Distortions (RSD) with DESI
or 4MOST, even though there are fewer objects. For our second
case, we use semi-analytic simulations and a prescription for the SNe Ia rate
as a function of stellar mass and star formation rate to predict the number of
LSST SNe IA whose host redshifts may already have been obtained with the
Taipan+WALLABY surveys, or with a future multi-object spectroscopic survey. We
find and SN Ia with host redshifts for these cases
respectively. Whilst this is only a fraction of the total LSST-detected SNe Ia,
they could be used to significantly augment and improve the growth rate
constraints compared to only RSD. Ultimately, we find that combining LSST SNe
Ia with large numbers of galaxy redshifts will provide the most powerful probe
of large scale gravity in the regime over the coming decades.Comment: 12 pages, 1 table, 5 figures. Accepted for publication in ApJ. The
Fisher matrix forecast code used in this paper can be found at:
https://github.com/CullanHowlett/PV_fisher. Updated to fix error in Eq. 1
(thanks to Eric Linder for pointing this out
Polycyclic Aromatic Hydrocarbon in the Central Region of the Seyfert 2 Galaxy NGC1808
We present mid infrared (MIR) spectra of the Seyfert 2 (Sy 2) galaxy NGC
1808, obtained with the Gemini's Thermal-Region Camera Spectrograph (T-ReCS) at
a spatial resolution of 26 pc. The high spatial resolution allowed us to detect
bright polycyclic aromatic hydrocarbons (PAHs) emissions at 8.6micron and
11.3micron in the galaxy centre (26 pc) up to a radius of 70 pc from the
nucleus. The spectra also present [Ne ii]12.8micron ionic lines, and H2
S(2)12.27micron molecular gas line. We found that the PAHs profiles are similar
to Peeters's A class, with the line peak shifted towards the blue. The
differences in the PAH line profiles also suggests that the molecules in the
region located 26 pc NE of the nucleus are more in the neutral than in the
ionised state, while at 26 pc SW of the nucleus, the molecules are mainly in
ionised state. After removal of the underlying galaxy contribution, the nuclear
spectrum can be represented by a Nenkova's clumpy torus model, indicating that
the nucleus of NGC 1808 hosts a dusty toroidal structure with an angular cloud
distribution of sigma = 70degree, observer's view angle i = 90degree, and an
outer radius of R0 = 0.55 pc. The derived column density along the line of
sight is NH = 1.5 x 10^24 cm-2, which is sufficient to block the hard radiation
from the active nucleus, and would explain the presence of PAH molecules near
to the NGC 1808's active nucleus.Comment: Accepted by MNRAS 2012 December
Non-Markovian continuous-time quantum walks on lattices with dynamical noise
We address the dynamics of continuous-time quantum walks on one-dimensional
disordered lattices inducing dynamical noise in the system. Noise is described
as time-dependent fluctuations of the tunneling amplitudes between adjacent
sites, and attention is focused on non-Gaussian telegraph noise, going beyond
the usual assumption of fast Gaussian noise. We observe the emergence of two
different dynamical behaviors for the walker, corresponding to two opposite
noise regimes: slow noise (i.e. strong coupling with the environment) confines
the walker into few lattice nodes, while fast noise (weak coupling) induces a
transition between quantum and classical diffusion over the lattice. A phase
transition between the two dynamical regimes may be observed by tuning the
ratio between the autocorrelation time of the noise and the coupling between
the walker and the external environment generating the noise. We also address
the non-Markovianity of the quantum map by assessing its memory effects, as
well as evaluating the information backflow to the system. Our results suggest
that the non-Markovian character of the evolution is linked to the dynamical
behavior in the slow noise regime, and that fast noise induces a Markovian
dynamics for the walker.Comment: 10 pages, 8 figure
Continuous-time quantum walks on dynamical percolation graphs
We address continuous-time quantum walks on graphs in the presence of time-
and space-dependent noise. Noise is modeled as generalized dynamical
percolation, i.e. classical time-dependent fluctuations affecting the tunneling
amplitudes of the walker. In order to illustrate the general features of the
model, we review recent results on two paradigmatic examples: the dynamics of
quantum walks on the line and the effects of noise on the performances of
quantum spatial search on the complete and the star graph. We also discuss
future perspectives, including extension to many-particle quantum walk, to
noise model for on-site energies and to the analysis of different noise
spectra. Finally, we address the use of quantum walks as a quantum probe to
characterize defects and perturbations occurring in complex, classical and
quantum, networks.Comment: 7 pages, 4 figures. Accepted for publication in EPL Perspective
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