8,966 research outputs found
Manipulating Light Pulses via Dynamically Controlled Photonic Bandgap
When a resonance associated with electromagnetically induced transparency
(EIT) in an atomic ensemble is modulated by an off-resonant standing light
wave, a band of frequencies can appear for which light propagation is
forbidden. We show that dynamic control of such a bandgap can be used to
coherently convert a propagating light pulse into a stationary excitation with
non-vanishing photonic component. This can be accomplished with high efficiency
and negligble noise even at a level of few-photon quantum fields thereby
facilitating possible applications in quantum nonlinear optics and quantum
information.Comment: 4 pages, 3 figure
Shaping quantum pulses of light via coherent atomic memory
We describe a technique for generating pulses of light with controllable
photon numbers, propagation direction, timing, and pulse shapes. The technique
is based on preparation of an atomic ensemble in a state with a desired number
of atomic spin excitations, which is later converted into a photon pulse.
Spatio-temporal control over the pulses is obtained by exploiting long-lived
coherent memory for photon states and electromagnetically induced transparency
(EIT) in an optically dense atomic medium. Using photon counting experiments we
observe generation and shaping of few-photon sub-Poissonian light pulses. We
discuss prospects for controlled generation of high-purity n-photon Fock states
using this technique.Comment: 4 pages, 4 figure
Nonlinear optics with stationary pulses of light
We show that the recently demonstrated technique for generating stationary
pulses of light [Nature {\bf 426}, 638 (2003)] can be extended to localize
optical pulses in all three spatial dimensions in a resonant atomic medium.
This method can be used to dramatically enhance the nonlinear interaction
between weak optical pulses. In particular, we show that an efficient Kerr-like
interaction between two pulses can be implemented as a sequence of several
purely linear optical processes. The resulting process may enable coherent
interactions between single photon pulses.Comment: 4 pages, 2 figure
Aperiodic quantum XXZ chains: Renormalization-group results
We report a comprehensive investigation of the low-energy properties of
antiferromagnetic quantum XXZ spin chains with aperiodic couplings. We use an
adaptation of the Ma-Dasgupta-Hu renormalization-group method to obtain
analytical and numerical results for the low-temperature thermodynamics and the
ground-state correlations of chains with couplings following several two-letter
aperiodic sequences, including the quasiperiodic Fibonacci and other
precious-mean sequences, as well as sequences inducing strong geometrical
fluctuations. For a given aperiodic sequence, we argue that in the easy-plane
anisotropy regime, intermediate between the XX and Heisenberg limits, the
general scaling form of the thermodynamic properties is essentially given by
the exactly-known XX behavior, providing a classification of the effects of
aperiodicity on XXZ chains. We also discuss the nature of the ground-state
structures, and their comparison with the random-singlet phase, characteristic
of random-bond chains.Comment: Minor corrections; published versio
Bayesian Updating Rules in Continuous Opinion Dynamics Models
In this article, I investigate the use of Bayesian updating rules applied to
modeling social agents in the case of continuos opinions models. Given another
agent statement about the continuous value of a variable , we will see that
interesting dynamics emerge when an agent assigns a likelihood to that value
that is a mixture of a Gaussian and a Uniform distribution. This represents the
idea the other agent might have no idea about what he is talking about. The
effect of updating only the first moments of the distribution will be studied.
and we will see that this generates results similar to those of the Bounded
Confidence models. By also updating the second moment, several different
opinions always survive in the long run. However, depending on the probability
of error and initial uncertainty, those opinions might be clustered around a
central value.Comment: 14 pages, 5 figures, presented at SigmaPhi200
Professional barriers and facilitators to using stratified care approaches for managing non-specific low back pain: a qualitative study with Canadian physiotherapists and chiropractors
Background: Recent clinical practice guidelines for the management of non-specific low back pain (LBP) recommend using stratified care approaches. To date, no study has assessed barriers and facilitators for health professionals in using stratified care approaches for managing non-specific LBP in the Canadian primary care setting. This study aimed to identify and contrast barriers and facilitators to using the stratified care approaches for non-specific LBP among Canadian physiotherapists and chiropractors. Methods: Individual telephone interviews, underpinned by the Theoretical Domains Framework (TDF), explored beliefs and attitudes about, and identified barriers and facilitators to the use of stratified care approaches for managing non-specific LBP in a purposive sample of 13 chiropractors and 14 physiotherapists between September 2015 and June 2016. Interviews were digitally recorded, transcribed verbatim and analysed by two independent assessors using directed content analysis. Results: Three and seven TDF domains were identified as likely relevant for physiotherapists and chiropractors, respectively. Shared key beliefs (and relevant domains of the TDF) for both physiotherapists and chiropractors included: lack of time, cost, and expertise (Environmental Context and Resources); and consulting more experienced colleagues and chronic patients with important psychological overlay (Social Influences). Unique key domains were identified among physiotherapists: incompatibility with achieving other objectives (Goals), and chiropractors: confidence in using stratified care approaches (Beliefs about Capabilities); intention to use stratified care approaches (Intentions); awareness and agreement with stratified care approaches (Knowledge); assessment of readiness for change and intentional planning behaviour (Behavioural Regulation); and improving the management of non-specific LBP patients and the uptake of evidence-based practice (Beliefs about Consequences). Conclusions: Several shared and unique barriers and facilitators to using the stratified care approaches for non-specific LBP among Canadian physiotherapists and chiropractors were identified. Findings may help inform the design of tailored theory-based knowledge translation interventions to increase the uptake of stratified care approaches in clinical practice. © The Author(s). 2019
Seiberg Duality and e+ e- Experiments
Seiberg duality in supersymmetric gauge theories is the claim that two
different theories describe the same physics in the infrared limit. However,
one cannot easily work out physical quantities in strongly coupled theories and
hence it has been difficult to compare the physics of the electric and magnetic
theories. In order to gain more insight into the equivalence of two theories,
we study the ``e+ e-'' cross sections into ``hadrons'' for both theories in the
superconformal window. We describe a technique which allows us to compute the
cross sections exactly in the infrared limit. They are indeed equal in the
low-energy limit and the equality is guaranteed because of the anomaly matching
condition. The ultraviolet behavior of the total ``e+ e-'' cross section is
different for the two theories. We comment on proposed non-supersymmetric
dualities. We also analyze the agreement of the ``\gamma\gamma'' and ``WW''
scattering amplitudes in both theories, and in particular try to understand if
their equivalence can be explained by the anomaly matching condition.Comment: 24 pages, 2 figures, uses psfi
Cooperative effects in nuclear excitation with coherent x-ray light
The interaction between super-intense coherent x-ray light and nuclei is
studied theoretically. One of the main difficulties with driving nuclear
transitions arises from the very narrow nuclear excited state widths which
limit the coupling between laser and nuclei. In the context of direct
laser-nucleus interaction, we consider the nuclear width broadening that occurs
when in solid targets, the excitation caused by a single photon is shared by a
large number of nuclei, forming a collective excited state. Our results show
that for certain isotopes, cooperative effects may lead to an enhancement of
the nuclear excited state population by almost two orders of magnitude.
Additionally, an update of previous estimates for nuclear excited state
population and signal photons taking into account the experimental advances of
the x-ray coherent light sources is given. The presented values are an
improvement by orders of magnitude and are encouraging for the future prospects
of nuclear quantum optics.Comment: 22 pages, 4 figures, 5 tables; updated to the published version, one
additional results tabl
Extended Initiality for Typed Abstract Syntax
Initial Semantics aims at interpreting the syntax associated to a signature
as the initial object of some category of 'models', yielding induction and
recursion principles for abstract syntax. Zsid\'o proves an initiality result
for simply-typed syntax: given a signature S, the abstract syntax associated to
S constitutes the initial object in a category of models of S in monads.
However, the iteration principle her theorem provides only accounts for
translations between two languages over a fixed set of object types. We
generalize Zsid\'o's notion of model such that object types may vary, yielding
a larger category, while preserving initiality of the syntax therein. Thus we
obtain an extended initiality theorem for typed abstract syntax, in which
translations between terms over different types can be specified via the
associated category-theoretic iteration operator as an initial morphism. Our
definitions ensure that translations specified via initiality are type-safe,
i.e. compatible with the typing in the source and target language in the
obvious sense. Our main example is given via the propositions-as-types
paradigm: we specify propositions and inference rules of classical and
intuitionistic propositional logics through their respective typed signatures.
Afterwards we use the category--theoretic iteration operator to specify a
double negation translation from the former to the latter. A second example is
given by the signature of PCF. For this particular case, we formalize the
theorem in the proof assistant Coq. Afterwards we specify, via the
category-theoretic iteration operator, translations from PCF to the untyped
lambda calculus
Quantitative atomic spectroscopy for primary thermometry
Quantitative spectroscopy has been used to measure accurately the
Doppler-broadening of atomic transitions in Rb vapor. By using a
conventional platinum resistance thermometer and the Doppler thermometry
technique, we were able to determine with a relative uncertainty of
, and with a deviation of from the
expected value. Our experiment, using an effusive vapour, departs significantly
from other Doppler-broadened thermometry (DBT) techniques, which rely on weakly
absorbing molecules in a diffusive regime. In these circumstances, very
different systematic effects such as magnetic sensitivity and optical pumping
are dominant. Using the model developed recently by Stace and Luiten, we
estimate the perturbation due to optical pumping of the measured value
was less than . The effects of optical pumping on atomic and
molecular DBT experiments is mapped over a wide range of beam size and
saturation intensity, indicating possible avenues for improvement. We also
compare the line-broadening mechanisms, windows of operation and detection
limits of some recent DBT experiments
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