Auswahl der wissenschaftlichen Literatur zum Thema „Mélanges dégénérés quantiques“
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Dissertationen zum Thema "Mélanges dégénérés quantiques"
Salez, Thomas. „Vers les mélanges quantiques dégénérés d'atomes fermioniques“. Phd thesis, Ecole Normale Supérieure de Paris - ENS Paris, 2011. http://tel.archives-ouvertes.fr/tel-00636899.
Der volle Inhalt der QuellePichery, Annie. „Theoretical study of quantum gas experiments in an Earth-orbiting research laboratory“. Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP010.
Der volle Inhalt der QuelleOne of the major goals of fundamental physics is to unify general relativity, which describes macroscopic phenomena driven by the influence of gravity, with quantum mechanics, which focuses on effects at microscopic scales. Ensembles of cold atoms, as massive quantum objects, lie at the crossroads of both theories and appear as a test object of choice. They can be used to test theories that postulate a violation of Einstein's Equivalence Principles, in particular a violation of the Universality of Free Fall (UFF).Recent proposals suggest using mixtures of Bose-Einstein condensates (BEC) as sources for precision atom interferometry to perform UFF. These have the potential to match the precision of the best tests with classical test masses performed during the MICROSCOPE mission, and may even provide better results in the long term. The realization of experiments in microgravity, where atoms can float for long periods of time, allows longer interrogation times, thus increasing the performance of matter-wave sensors. To optimize the implementation of UFF tests, one needs exquisite control of the atoms due to stringent requirements on the error budget. In this work, we focus on the design of the input state with control over the position and velocity of the atom clouds, as well as their size evolution.The experiments studied here are designed with atom chip setups that manipulate atoms with magnetic traps. Most of the applications presented are experiments performed in the NASA Cold Atom Laboratory (CAL) aboard the International Space Station as part of the Consortium for Ultracold Atoms in Space (CUAS). This multi-user BEC machine allows the manipulation of single species BEC at its installation as well as dual species mixtures after upgrades. Following this chronology, we first study the dynamics of single species BEC and then extend the work to the manipulation of an interacting mixture of two BECs. The first step after calibrating the chip model is to design a fast and robust transport protocol to move the atoms away from the atom chip. We present and use a Shortcut-To-Adiabaticity (STA) protocol, based on reverse engineering, to transport the BEC and meet the requirements of position control at the sub- extmu m level and velocity control at the hundreds of extmu m/s level. The free expansion of the atom cloud with its inherent atomic density drop makes signal detection difficult. By analogy with light, it is possible to collimate the atom cloud with atomic lenses using the Delta-Kick Collimation (DKC) technique. Application to CAL resulted in expansion energies in the tens of pK level. To simulate the imaging process and to support the data analysis, theoretical models are presented that take into account the resolution effects of the camera and the frame transformations associated with the orientation of the camera or the orientation of the trapping potential with respect to the atom chip.Space allows the operation of Bose-Einstein condensate mixtures under miscibility conditions not possible on the ground. The colocation of the trap center for the different species in microgravity can lead to different topologies of the trap ground state. Moreover, the interaction energy between the species, which is almost negligible in the ground state, plays a significant role in the dynamics of the mixture during its transport. However, the simulation of the dynamics of interacting dual-species BEC mixtures is computationally challenging, particularly due to the long expansion times. In this work, scaling techniques to overcome these limitations are presented and illustrated in the case of space experiments in CAL and aboard sounding rockets. Such scaled-grid approaches make it possible to simulate long transports with free expansion times on the order of seconds, which would not be feasible with a fixed-grid approach on reasonable time scales, not to mention the problems of memory usage
Sievers, Franz. „Ultracold Fermi mixtures and simultaneous sub-Doppler laser cooling of fermionic 6Li and 40K“. Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066221/document.
Der volle Inhalt der QuelleThis thesis reports on novel techniques for experimental studies of ultracold, fermionic lithium and potassium quantum gases. The new parts of our 6Li-40K apparatus are described and characterised. We present a narrow-linewidth, all-solid-state laser source, emitting 5W at 671 nm. We employ the laser source in the context of a novel sub-Doppler cooling mechanism, operating on the D1 atomic transition of alkali atoms, for laser cooling of lithium. This D1 molasses allows us to simultaneously cool a mixture of 6Li and 40K atoms to deep sub-Doppler temperatures, while retaining large atom numbers and high atomic densities. The measured phase space densities after the molasses phase are on the order of 10-4 for both 6Li and 40K. The D1 laser cooling paves the way for fast evaporation to quantum degeneracy in magnetic and optical traps. We present the evaporative cooling of 40K atoms. The evaporation starts in an optically plugged magnetic quadrupole trap and continues in an optical dipole trap. At the end of the evaporation, we obtain a quantum degenerate spin-mixture of 40K atoms, with more than 7x105 atoms in each of the two spin states and T/TF<0.34
Barbier, Margaux. „Génération de paires de photons corrélés par mélange à quatre ondes spontané dans des fibres microstructurées à coeur liquide“. Thesis, Palaiseau, Institut d'optique théorique et appliquée, 2014. http://www.theses.fr/2014IOTA0011/document.
Der volle Inhalt der QuelleQuantum telecommunication technologies rely on correlated photon pair sources, which are often based on the third-order nonlinear process of spontaneous four-wave mixing in silica-core photonic crystal fibres. A fibred architecture is advantageous because it minimizes the coupling losses between the optical source and the other components of quantum communication networks. Moreover, using a photonic crystal fibre rather than a conventional silica fibre offers the possibility of improving the photon generation (thanks to a small effective core area) and extending the wavelength coverage (thanks to dispersion management through the microstructuration design). However, the performances of silica-core photonic crystal fibre sources are limited in terms of quantum purity, because of the ubiquitous spontaneous Raman scattering process, which is a source of uncorrelated broadband noise photons in silica. We propose an original solution to this Raman problem by replacing the silica core by a liquid core, thanks to a hollow-core photonic crystal fibre filled with a nonlinear liquid. We actually performed the first experimental demonstration of the generation of correlated photon pairs in a liquid-core fibre, and demonstrated that, thanks to the specific Raman properties of liquids (which usually exhibit thin-line Raman spectra), it is possible to reduce the Raman noise level by several orders of magnitude. This work opens the way for the development of high quantum quality correlated photon pair fibred sources
Kretzschmar, Norman. „Experiments with Ultracold Fermi Gases : quantum Degeneracy of Potassium-40 and All-solid-state Laser Sources for Lithium“. Thesis, Paris, Ecole normale supérieure, 2015. http://www.theses.fr/2015ENSU0012/document.
Der volle Inhalt der QuelleThis thesis presents novel techniques for the experimental study of ultracold quantum gases of fermionic lithium and potassium atoms. In the first part of this thesis, we describe the design and characterization of the new components of our experimental apparatus capable of trapping and cooling simultaneously $^6$Li and $^{40}$K atoms to ultracold temperatures. We report on a novel sub-Doppler cooling mechanism, operating on the D$_1$ line transition of alkali atoms, for laser cooling of lithium and potassium. The measured phase space densities after this molasses phase are on the order of $10^{-4}$ for both $^6$Li and $^{40}$K. We present the forced evaporative cooling of $^{40}$K atoms, starting in an optically plugged magnetic quadrupole trap and continuing in an optical dipole trap. In this context, we report on the production of a quantum degenerate Fermi gas of $1.5\times10^5$ atoms $^{40}$K in a crossed dipole trap with $T/T_{_F} = 0.17$, paving the way for the study of strongly interacting superfluids of $^{40}$K. In the second part of this thesis, we present a narrow-linewidth, all-solid-state laser source, emitting 5.2 W in the vicinity of the lithium D-line transitions at 671 nm. The source is based on a diode-end-pumped unidirectional ring laser operating on the 1342 nm transition of Nd:YVO$_4$, capable of producing 6.5 W of single-mode light delivered in a diffraction-limited beam. We report on three different approaches for second-haromonic generation of its output beam, namely by employing an enhancement cavity containing a ppKTP crystal, intracavity frequency doubling and a ppZnO:LN waveguide structure
Lopes, Raphael. „An atomic Hong-Ou-Mandel experiment“. Thesis, Palaiseau, Institut d'optique théorique et appliquée, 2015. http://www.theses.fr/2015IOTA0001/document.
Der volle Inhalt der QuelleIn this thesis, we report the first realisation of the Hong–Ou–Mandel experiment with massive particles in momentum space. This milestone experiment was originally performed in quantum optics: two photons arriving simultaneously at the input ports of a 50:50 beam-splitter always emerge together in one of the output ports. The effect leads to a reduction of coincidence counts which translates into a dip when particles are indistinguishable. We performed the experiment with metastable helium atoms where the specificities of the Micro-Channel-Plate detector allows one to recover the momentum vector of each individual atom.After listing the necessary tools to perform this experiment with atoms, the experimental sequence is discussed and the results are presented. In particular we measured a coincidence count reduction that cannot be explained through any simple classical model. This corresponds to the signature of a two-particle interference, and confirms that our atomic pair source produces beams which have highly correlated populations and are well mode matched. This opens the prospect of testing Bell’s inequalities involving mechanical observables of massive particles, such as momentum, using methods inspired by quantum optics. It also demonstrates a new way to produce and benchmark twin-atom pairs that may be of interest for quantum information processing