20,419 research outputs found
Real-space Hopfield diagonalization of inhomogeneous dispersive media
We introduce a real-space technique able to extend the standard Hopfield
approach commonly used in quantum polaritonics to the case of inhomogeneous
lossless materials interacting with the electromagnetic field. We derive the
creation and annihilation polaritonic operators for the system normal modes as
linear, space-dependent superpositions of the microscopic light and matter
fields, and we invert the Hopfield transformation expressing the microscopic
fields as functions of the polaritonic operators. As an example, we apply our
approach to the case of a planar interface between vacuum and a polar
dielectric, showing how we can consistently treat both propagative and surface
modes, and express their nonlinear interactions, arising from phonon
anharmonicity, as polaritonic scattering terms. We also show that our theory
can be naturally extended to the case of dissipative materials
Theoretical Investigation of Phonon Polaritons in SiC Micropillar Resonators
Of late there has been a surge of interest in localised phonon polariton
resonators which allow for sub-diffraction confinement of light in the
mid-infrared spectral region by coupling to optical phonons at the surface of
polar dielectrics. Resonators are generally etched on deep substrates which
support propagative surface phonon polariton resonances. Recent experimental
work has shown that understanding the coupling between localised and
propagative surface phonon polaritons in these systems is vital to correctly
describe the system resonances. In this paper we comprehensively investigate
resonators composed of arrays of cylindrical SiC resonators on SiC substrates.
Our bottom-up approach, starting from the resonances of single, free standing
cylinders and isolated substrates, and exploiting both numerical and analytical
techniques, allows us to develop a consistent understanding of the parameter
space of those resonators, putting on firmer ground this blossoming technology.Comment: 10 Pages, 8 Figure
Excitonic spectral features in strongly-coupled organic polaritons
Starting from a microscopic model, we investigate the optical spectra of
molecules in strongly-coupled organic microcavities examining how they might
self-consistently adapt their coupling to light. We consider both rotational
and vibrational degrees of freedom, focusing on features which can be seen in
the peak in the center of the spectrum at the bare excitonic frequency. In both
cases we find that the matter-light coupling can lead to a self-consistent
change of the molecular states, with consequent temperature-dependent
signatures in the absorption spectrum. However, for typical parameters, these
effects are much too weak to explain recent measurements. We show that another
mechanism which naturally arises from our model of vibrationally dressed
polaritons has the right magnitude and temperature dependence to be at the
origin of the observed data.Comment: 14 pages, 6 figur
Observing the evolution of a quantum system that does not evolve
This article deals with the problem of gathering information on the time
evolution of a single metastable quantum system whose evolution is impeded by
the quantum Zeno effect. It has been found it is in principle possible to
obtain some information on the time evolution and, depending on the specific
system, even to measure its average decay rate, even if the system does not
undergo any evolution at all.Comment: Two over three PRA referees didn't like the old title... And no more
quantum circuits in the new versio
Accurate Determination of Conformational Transitions in Oligomeric Membrane Proteins
The structural dynamics governing collective motions in oligomeric membrane proteins play key roles in vital biomolecular processes at cellular membranes. In this study, we present a structural refinement approach that combines solid-state NMR experiments and molecular simulations to accurately describe concerted conformational transitions identifying the overall structural, dynamical, and topological states of oligomeric membrane proteins. The accuracy of the structural ensembles generated with this method is shown to reach the statistical error limit, and is further demonstrated by correctly reproducing orthogonal NMR data. We demonstrate the accuracy of this approach by characterising the pentameric state of phospholamban, a key player in the regulation of calcium uptake in the sarcoplasmic reticulum, and by probing its dynamical activation upon phosphorylation. Our results underline the importance of using an ensemble approach to characterise the conformational transitions that are often responsible for the biological function of oligomeric membrane protein states
Multitarget drug discovery for Alzheimer's disease: triazinones as BACE-1 and GSK-3β inhibitors
Cranial neuralgias: from physiopathology to pharmacological treatment
Cranial neuralgias are paroxysmal painful disorders of the head characterised by some shared features such as unilaterality of symptoms, transience and recurrence of attacks, superficial and "shock-like" quality of pain and the presence of triggering factors. Although rare, these disorders must be promptly recognised as they harbour a relatively high risk for underlying compressive or inflammatory disease. Nevertheless, misdiagnosis is frequent. Trigeminal and glossopharyngeal neuralgias are sustained in most cases by a neurovascular conflict in the posterior fossa resulting in a hyperexcitability state of the trigeminal circuitry. If the aetiology of trigeminal neuralgia (TN) and other typical neuralgias must be brought back to the peripheral injury, their pathogenesis could involve central allodynic mechanisms, which, in patients with inter-critical pain, also engage the nociceptive neurons at the thalamic-cortical level. Currently available medical treatments for TN and other cranial neuralgias are reviewed
- …