Search results for " ELECTRODYNAMICS"
showing 10 items of 813 documents
Metal-Insulator Transition of Solid Hydrogen by the Antisymmetric Shadow Wave Function
2016
We revisit the pressure-induced metal-insulator-transition of solid hydrogen by means of variational quantum Monte Carlo simulations based on the antisymmetric shadow wave function. In order to facilitate studying the electronic structure of large-scale fermionic systems, the shadow wave function formalism is extended by a series of technical improvements, such as a revised optimization method for the employed shadow wave function and an enhanced treatment of periodic systems with long-range interactions. It is found that the superior accuracy of the antisymmetric shadow wave function results in a significantly increased transition pressure.
Cavity-based architecture to preserve quantum coherence and entanglement
2015
Quantum technology relies on the utilization of resources, like quantum coherence and entanglement, which allow quantum information and computation processing. This achievement is however jeopardized by the detrimental effects of the environment surrounding any quantum system, so that finding strategies to protect quantum resources is essential. Non-Markovian and structured environments are useful tools to this aim. Here we show how a simple environmental architecture made of two coupled lossy cavities enables a switch between Markovian and non-Markovian regimes for the dynamics of a qubit embedded in one of the cavity. Furthermore, qubit coherence can be indefinitely preserved if the cavit…
Propagating single photons from an open cavity: Description from universal quantization
2022
Over the last decades, quantum optics has evolved from high quality factor cavities in the early experiments toward new cavity designs involving leaky modes. Despite very reliable models, in the concepts of cavity quantum electrodynamics, photon leakage is most of the time treated phenomenologically. Here, we take a different approach, and starting from first principles, we define an inside-outside representation which is derived from the original true-mode representation, in which one can determine effective Hamiltonian and Poynting vector. Contrary to the phenomenological model, they allow a full description of a leaking single photon produced in the cavity and propagating in free space. …
Génération et interfaçage de lumière à photon unique et contrôle de la dynamique atomique ultra-rapide pour l’information quantique
2010
We develop a robust and realistic mechanism for the generation of indistinguishable single-photon (SP) pulses with identical frequency and polarization. They are produced on demand from a coupled double-Raman atom-cavity system driven by a sequence of laser pump pulses. This scheme features a high efficiency, the ability to produce a sequence of narrow-band SP pulses with a delay determined only by the pump repetition rate, and simplicity of the system free from complications such as repumping process and environmental dephasing. We propose and analyze a simple scheme of parametric frequency conversion for optical quantum information in cold atomic ensembles. Its remarkable properties are m…
Screening effects in Relativistic Models of Dense Matter at Finite Temperature
1998
We investigate screening effects of the medium on the potential interaction between two static 'charges' for different models of dense plasmas in the one-boson exchange approximation. The potential can exhibit an oscillatory behavior, which is related to the analytic structure of the corresponding boson propagators in the complex $q$-plane. We have first revisited the one-pion exchange in a nuclear medium. In addition to Friedel oscillations, which are associated to branch cuts in the $q$-plane, there appears another oscillatory component, which arises from a pole on the pion propagator. This pole is located appart from the axes, giving rise to an oscillating Yukawa-like potential. Therefor…
Gluon and ghost propagators in the Landau gauge: Deriving lattice results from Schwinger-Dyson equations
2008
We show that the application of a novel gauge invariant truncation scheme to the Schwinger-Dyson equations of QCD leads, in the Landau gauge, to an infrared finite gluon propagator and a divergent ghost propagator, in qualitative agreement with recent lattice data.
Gluon mass and freezing of the QCD coupling
2007
Infrared finite solutions for the gluon propagator of pure QCD are obtained from the gauge-invariant non-linear Schwinger-Dyson equation formulated in the Feynman gauge of the background field method. These solutions may be fitted using a massive propagator, with the special characteristic that the effective mass employed drops asymptotically as the inverse square of the momentum transfer, in agreement with general operator-product expansion arguments. Due to the presence of the dynamical gluon mass the strong effective charge extracted from these solutions freezes at a finite value, giving rise to an infrared fixed point for QCD.
Pinch technique to all orders
2002
The generalization of the pinch technique to all orders in perturbation theory is presented. The effective Green's functions constructed with this procedure are singled out in a unique way through the full exploitation of the underlying Becchi-Rouet-Stora-Tyutin symmetry. A simple all-order correspondence between the pinch technique and the background field method in the Feynman gauge is established. Comment: 10 pages, 4 figures; one reference added, typos corrected; final version to match the pubblished one
Towards a consistent estimate of the chiral low-energy constants
2006
Guided by the large-N_C limit of QCD, we construct the most general chiral resonance Lagrangian that can generate chiral low-energy constants up to O(p^6). By integrating out the resonance fields, the low-energy constants are parametrized in terms of resonance masses and couplings. Information on those couplings and on the low-energy constants can be extracted by analysing QCD Green functions of currents both for large and small momenta. The chiral resonance theory generates Green functions that interpolate between QCD and chiral perturbation theory. As specific examples we consider the VAP and SPP Green functions.
One-loop renormalization of Resonance Chiral Theory: scalar and pseudoscalar resonances
2005
We consider the Resonance Chiral Theory with one multiplet of scalar and pseudoscalar resonances, up to bilinear couplings in the resonance fields, and evaluate its beta-function at one-loop with the use of the background field method. Thus we also provide the full set of operators that renormalize the theory at one loop and render it finite.