1,326 research outputs found
Universal Constants, Standard Models and Fundamental Metrology
Taking into account four universal constants, namely the Planck's constant
, the velocity of light , the constant of gravitation and the
Boltzmann's constant leads to structuring theoretical physics in terms of
three theories each taking into account a pair of constants: the quantum theory
of fields ( and ), the general theory of relativity ( and ) and
quantum statistics ( and ). These three theories are not yet unified but,
together, they underlie the standard models that allow a satisfactory
phenomenological description of all experimental or observational data, in
particle physics and in cosmology and they provide, through the modern
interpretation of quantum physics, fundamental metrology with a reliable
theoretical basis
An Effective Strong Gravity induced by QCD
We show that, when quantized on a curved ``intra-hadronic background'', QCD
induces an effective pseudo gravitational interaction with gravitational and
cosmological constants in the GeV range.Comment: 9 pages, latex, no figures; to appear in Mod.Phys.Lett.
Decoherence in quantum dots due to real and virtual transitions: a non-perturbative calculation
We investigate theoretically acoustic phonon induced decoherence in quantum
dots. We calculate the dephasing of fundamental (interband or intraband)
optical transitions due to real and virtual transitions with higher energy
levels. Up to two acoustic phonon processes (absorption and/or emission) are
taken into account simultaneously in a non-perturbative manner. An analytic
expression of acoustic phonon induced broadening is given as a function of the
electron-phonon matrix elements and is physically interpreted. The theory is
applied to the dephasing of intersublevel transitions in self-assembled quantum
dots.Comment: 8 pages, 4 figure
Parton-Hadron duality in event generators
The validity of local parton-hadron duality within the framework of HERWIG
and JETSET event generators is investigated. We concentrate on annihilations in LEP 2 energy range as these interactions provide
theoretically the cleanest condition for the discussion of this concept.Comment: PRA-HEP-92/14, 10 pages and 7 PS figures obtainable upon request,
LATEX. email transmission errors corrected. Requests for figures can be sent
on the above ID or to CHYLA@CSPGAS1
Thermal breakdown of coherent backscattering: a case study of quantum duality
We investigate coherent backscattering of light by two harmonically trapped
atoms in the light of quantitative quantum duality. Including recoil and
Doppler shift close to an optical resonance, we calculate the interference
visibility as well as the amount of which-path information, both for zero and
finite temperature.Comment: published version with minor changes and an added figur
The effect of extreme confinement on the nonlinear-optical response of quantum wires
This work focuses on understanding the nonlinear-optical response of a 1-D
quantum wire embedded in 2-D space when quantum-size effects in the transverse
direction are minimized using an extremely weighted delta function potential.
Our aim is to establish the fundamental basis for understanding the effect of
geometry on the nonlinear-optical response of quantum loops that are formed
into a network of quantum wires. Using the concept of leaky quantum wires, it
is shown that in the limit of full confinement, the sum rules are obeyed when
the transverse infinite-energy continuum states are included. While the
continuum states associated with the transverse wavefunction do not contribute
to the nonlinear optical response, they are essential to preserving the
validity of the sum rules. This work is a building block for future studies of
nonlinear-optical enhancement of quantum graphs (which include loops and bent
wires) based on their geometry. These properties are important in quantum
mechanical modeling of any response function of quantum-confined systems,
including the nonlinear-optical response of any system in which there is
confinement in at leat one dimension, such as nanowires, which provide
confinement in two dimensions
Achieving ground-state polar molecular condensates by chainwise atom-molecule adiabatic passage
We generalize the idea of chainwise stimulated Raman adiabatic passage
(STIRAP) [Kuznetsova \textit{et al.} Phys. Rev. A \textbf{78}, 021402(R)
(2008)] to a photoassociation-based chainwise atom-molecule system, with the
goal of directly converting two-species atomic Bose-Einstein condensates (BEC)
into a ground polar molecular BEC. We pay particular attention to the
intermediate Raman laser fields, a control knob inaccessible to the usual
three-level model. We find that an appropriate exploration of both the
intermediate laser fields and the stability property of the atom-molecule
STIRAP can greatly reduce the power demand on the photoassociation laser, a key
concern for STIRAPs starting from free atoms due to the small Franck-Condon
factor in the free-bound transition.Comment: 8 pages, 2 figures, to appear in Phy. Rev.
The non dissipative damping of the Rabi oscillations as a "which-path" information
Rabi oscillations may be viewed as an interference phenomenon due to a
coherent superposition of different quantum paths, like in the Young's two-slit
experiment. The inclusion of the atomic external variables causes a non
dissipative damping of the Rabi oscillations. More generally, the atomic
translational dynamics induces damping in the correlation functions which
describe non classical behaviors of the field and internal atomic variables,
leading to the separability of these two subsystems. We discuss on the
possibility of interpreting this intrinsic decoherence as a "which-way"
information effect and we apply to this case a quantitative analysis of the
complementarity relation as introduced by Englert [Phys. Rev. Lett.
\textbf{77}, 2154 (1996)].Comment: 5 pages, 2 figure
Atomic detection in microwave cavity experiments: a dynamical model
We construct a model for the detection of one atom maser in the context of
cavity Quantum Electrodynamics (QED) used to study coherence properties of
superpositions of electromagnetic modes. Analytic expressions for the atomic
ionization are obtained, considering the imperfections of the measurement
process due to the probabilistic nature of the interactions between the
ionization field and the atoms. Limited efficiency and false counting rates are
considered in a dynamical context, and consequent results on the information
about the state of the cavity modes are obtained.Comment: 12 pages, 1 figur
Control of dipolar relaxation in external fields
We study dipolar relaxation in both ultra-cold thermal and Bose-condensed
chromium atom gases. We show three different ways to control dipolar
relaxation, making use of either a static magnetic field, an oscillatory
magnetic field, or an optical lattice to reduce the dimensionality of the gas
from 3D to 2D. Although dipolar relaxation generally increases as a function of
a static magnetic field intensity, we find a range of non-zero magnetic field
intensities where dipolar relaxation is strongly reduced. We use this resonant
reduction to accurately determine the S=6 scattering length of chromium atoms:
. We compare this new measurement to another new
determination of , which we perform by analysing the precise spectroscopy
of a Feshbach resonance in d-wave collisions, yielding . These two measurements provide by far the most precise determination of
to date. We then show that, although dipolar interactions are long-range
interactions, dipolar relaxation only involves the incoming partial wave
for large enough magnetic field intensities, which has interesting consequences
on the stability of dipolar Fermi gases. We then study ultra-cold chromium
gases in a 1D optical lattice resulting in a collection of independent 2D
gases. We show that dipolar relaxation is modified when the atoms collide in
reduced dimensionality at low magnetic field intensities, and that the
corresponding dipolar relaxation rate parameter is reduced by a factor up to 7
compared to the 3D case. Finally, we study dipolar relaxation in presence of
radio-frequency (rf) oscillating magnetic fields, and we show that both the
output channel energy and the transition amplitude can be controlled by means
of rf frequency and Rabi frequency.Comment: 25 pages, 17 figure
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