Universal Constants, Standard Models and Fundamental Metrology

Taking into account four universal constants, namely the Planck's constant $h$, the velocity of light $c$, the constant of gravitation $G$ and the Boltzmann's constant $k$ leads to structuring theoretical physics in terms of three theories each taking into account a pair of constants: the quantum theory of fields ($h$ and $c$), the general theory of relativity ($c$ and $G$) and quantum statistics ($h$ and $k$). 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 ${\rm e}^{+}{\rm e}^{-}$ 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

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

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

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: $a_6 = 103 \pm 4 a_0$. We compare this new measurement to another new determination of $a_6$, which we perform by analysing the precise spectroscopy of a Feshbach resonance in d-wave collisions, yielding $a_6 = 102.5 \pm 0.4 a_0$. These two measurements provide by far the most precise determination of $a_6$ to date. We then show that, although dipolar interactions are long-range interactions, dipolar relaxation only involves the incoming partial wave $l=0$ 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