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Atom laser experiments with Bose-Einstein condensates (BECs) performed in ground-based laboratories feature a coherent and directed beam of atoms which is accelerated by gravity. In microgravity the situation is fundamentally different because the dynamics is entirely determined by the repulsive interaction between the atoms and not by the gravitational force. As a result, the output of a space atom laser is a spherical wave slowly expanding away from the initial BEC.We present a thorough theoretical study of this new source of matter waves based on rf outcoupling which exhibits an isotropic distribution both in position and momentum even for an initially anisotropic trap. The unique geometry of such a freely expanding, shell-shaped BEC offers new possibilities for matter waves in microgravity and is complementary to other matter-wave sources prepared by delta-kick collimation or adiabatic expansion. Our work paves the way for the upcoming experimental realization of a space atom laser making use of NASA's Cold Atom Laboratory on the International Space Station., Comment: 36 pages, 9 figures, minor changes to match the published version

We present a compact atomic clock using cold rubidium atoms based on an isotropic light cooling, a Ramsey microwave interrogation and an absorption detection. Its technology readiness level is suitable to industrial transfer. We use a fibre optical bench, based on a frequency-doubled telecom laser. The isotropic light cooling technique allows us to cool down the atoms in 100 ms and works with a cycle time around 200 ms. We carried out measurements in simulated microgravity and obtained the narrowest fringes ever recorded in microgravity., 7 pages, 6 figures

As an energy-preserving variant of laser hybrid welding, laser-assisted arc welding uses laser powers of less than 1 kW. Recent studies have shown that the electrical conductivity of a TIG welding arc changes within the arc in case of a resonant interaction between laser radiation and argon atoms. This paper presents investigations on how to control the position of the arc root on the workpiece by means of the resonant interaction. Furthermore, the influence on the welding result is demonstrated. The welding tests were carried out on a cooled copper plate and steel samples with resonant and non-resonant laser radiation. Moreover, an analysis of the weld seam is presented.

Strong-field manipulation of autoionizing states is a crucial aspect of electronic quantum control. Recent measurements of the attosecond transient absorption spectrum (ATAS) of helium dressed by a few-cycle visible pulse [C. Ott, Nature (London) 516, 374 (2014)] provide evidence of the inversion of Fano profiles. With the support of accurate ab initio calculations that reproduce the results of the latter experiment, here we investigate the new physics that arise from ATAS when the laser intensity is increased. In particular, we show that (i) previously unnoticed signatures of the dark 2p2 1S doubly excited state are observed in the experimental spectrum, (ii) inversion of Fano profiles is predicted to be periodic in the laser intensity, and (iii) the ac Stark shift of the higher terms in the sp2,n+ autoionizing series exceeds the ponderomotive energy, which is the result of a genuine two-electron contribution to the polarization of the excited atom, We acknowledge computer time from the CCC-UAM and Marenostrum Supercomputer Centers and financial support from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement 290853 XCHEM, the MINECO project FIS2013-42002-R, the ERAChemistry Project PIM2010EEC-00751, the European COST Action XLIC CM1204, the Marie Curie ITN CORINF, and the CAM project NANOFRONTMAG. C.O. and T.P. acknowledge financial support by the Max-Planck Research Group Program of the Max-Planck Gesellschaft (MPG) and the European Research Council (ERC, Grant No. X-MuSiC-616783)

Strong-field manipulation of autoionizing states is a crucial aspect of electronic quantum control. Recent measurements of the attosecond transient absorption spectrum (ATAS) of helium dressed by a few-cycle visible pulse [C. Ott et al, Nature 516, 374 (2014)] provide evidence of the inversion of Fano profiles. With the support of accurate ab-initio calculations that reproduce the results of the latter experiment, here we investigate the new physics that arise from ATAS when the laser intensity is increased. In particular, we show that (i) previously unnoticed signatures of the dark 2p2 1S doubly excited state are observed in the experimental spectrum, (ii) inversion of Fano profiles is predicted to be periodic in the laser intensity, and (iii) the ac-Stark shift of the higher terms in the sp+2, n autoionizing series exceeds the ponderomotive energy, which is the result of a genuine two-electron contribution to the polarization of the excited atom.

We present a generalized model for the intensity dependent response of atoms in strong IR laser fields, describing deviations in the nonlinear response at the frequency of the driving field from the standard model (linear Kerr effect + plasma defocusing) based on the formation of the stable KH states. According to our numerical simulations, shaping the driving laser pulse allows one to reveal a prominent resonance structure in the Kerr response of an individual atom, which can only be explained by population transfer into excited KH states., CLEO®/Europe-IQEC 2013, May 12th to 16th, 2013, Munich, Germany

In this thesis we present ultracold sources using Bose-Einstein Condensates for atom interferometry and atomic physics applications. We produce a 87 Rb atom laser using an optical Raman out-coupling technique. The atoms are transferred from their initial magnetically trapped state to a state which is insensitive to magnetic fields and subsequently fall under gravity. We show that, in contrast to a standard Radio-Frequency (RF) out-coupling method, the initial momentum imparted to the atoms reduces the divergence and improves the spatial profile of the beam. Alternatively, we demon- strate that each of the two Raman beams can be used independently to provide efficient and coherent splitting of the atom laser using a fraction of back-reflected light. We also investigate theoretically the dynamics of RF out-coupled atom laser systems. Then we present details of significant improvements on the experimental setup used to condense metastable helium atoms (4He* ). We present the layout of a new laser system operated for trapping and cooling the atoms, as well as the optical configuration to transfer them into a dipole trap or an optical lattice. A channel electron multiplier is added to provide a non-destructive real-time detection method based on Penning collisions. Finally, we describe the design of a new magnetic trap with improved optical access, which we conceived and constructed to allow for 4He* Bose-Einstein condensation to be compatible with in-situ loading of the condensed gas into a 3 dimensional lattice., Dans ce mémoire nous présentons des sources ultra-froides utilisant des condensats de Bose-Einstein pour des applications en interféromètrie et physique atomiques. Nous produisons un laser à atomes de 87 Rb par couplage optique Raman. Initialement piégés magnétiquement, les atomes sont transférés dans un état insensible aux champs magnétiques et tombent sous l'effet de la gravité. Nous montrons qu'à l'inverse d'une méthode d'extraction Radio-Fréquence l'impulsion transférée aux atomes permet de réduire la divergence et d'améliorer le profil spatial du faisceau atomique. Nous prouvons que chacun des deux faisceaux Raman peut être utilisé indépendemment pour diffracter le laser à atomes de manière efficace et cohérente en utilisant une fraction de lumière rétro-diffusée. La dynamique des lasers à atomes extraits par couplage RF est également étudiée théoriquement. Nous détaillons ensuite les améliorations apportées au dispositif expérimental permettant de condenser des atomes d'hélium métastable (4He* ). Nous décrivons l'ensemble du nouveau système laser destiné au piégeage et au ralentissement des atomes, ainsi qu'à leur transfert dans un piège dipolaire ou un réseau optique. L'ajout d'un multiplicateur d'électrons fournit une méthode de détection non-destructive en temps réel fondée sur les collisions Penning. Enfin, nous présentons un nouveau piége magnétique à grande accessibilité optique, conçu et construit pour produire un condensat d'atomes 4He* et le transférer, in-situ, dans un réseau optique à 3 dimensions.

Efficient preparation and detection of the motional state of trapped ions is important in many experiments ranging from quantum computation to precision spectroscopy. We investigate the stimulated Raman adiabatic passage (STIRAP) technique for the manipulation of motional states in a trapped ion system. The presented technique uses a Raman coupling between two hyperfine ground states in $^{25}$Mg$^+$, implemented with delayed pulses, which removes a single phonon independent of the initial motional state. We show that for a thermal state the STIRAP population transfer is more efficient than a stimulated Raman Rabi pulse on a motional sideband. In contrast to previous implementations, a large detuning of more than 200 times the natural linewidth of the transition is used. This approach renders STIRAP suitable for atoms in which resonant laser fields would populate fluorescing excited states and thus impede the STIRAP process. We use the technique to measure the wavefunction overlap of excited motional states with the motional ground state. This is an important application for photon recoil spectroscopy and other force sensing applications that utilize the high sensitivity of the motional state of trapped ions to external fields. Furthermore, a determination of the ground state population enables a simple measurement of the ion's temperature., 17 pages, 7 figures

We use the theory of coupled Gross-Pitaevskii equations to derive an expression for the current density of the propagating atoms coupled out of the condensate under the influence of gravity. By describing the propagation vector of the atoms and using a theoretical definition of the coherence length, we calculate the coherence lengths of 37K, 141Ce, and 249Fm atom lasers numerically. Our calculation method is verified with the available experimental and theoretical data in the literature. The results showed a very good agreement.

Optical trapping as a viable means of exploring the physics of ultracold dilute atomic gases has revealed a new spectrum of physical phenomena. In particular, macroscopic and sudden occupation of the ground state below a critical temperature—-a phenomenon known as Bose-Einstein condensation—-has become an even richer system for the study of quantum mechanics, ultracold collisions, and many-body physics in general. Optical trapping liberates the spin degree of the BEC, making the order parameter vectorial (‘spinor BEC’), as opposed to the scalar order of traditional magnetically trapped condensates. The work described within is divided into two main efforts. The first encompasses the all-optical creation of a Bose-Einstein condensate in rubidium vapor. An all-optical path to spinor BEC (as opposed to transfer to an optical trap from a magnetic-trap condensate) was desired both for the simplicity of the experimental setup and also for the potential gains in speed of creation; evaporative cooling, the only known path to dilute-gas condensation, works only as efficiently as the rate of elastic collisions in the gas, a rate that starts out much higher in optical traps. The first all-optical BEC was formed elsewhere in 2001; the years following saw many groups worldwide seeking to create their own version. Our own all-optical spinor BEC, made with a single-beam dipole trap formed by a focused CO₂ laser, is described here, with particular attention paid to trap loading, measurement of trap parameters, and the use of a novel 780 nm high-power laser system. The second part describes initial experiments performed with the nascent condensate. The spinor properties of the condensate are documented, and a measurement is made of the density-dependent rate of spin mixing in the condensate. In addition, we demonstrate a novel dual-beam atom laser formed by outcoupling oppositely polarized components of the condensate, whose populations have been coherently evolved through spin dynamics. We drive coherent spin-mixing evolution through adiabatic compression of the initially weak trap. Such dual beams, nominally number-correlated through the angular momentum-conserving collision m=0 + m=0 ⇌ m=+1 + m=-1 have been proposed as tools to explore entanglement and squeezing in Bose-Einstein condensates.

International audience; Summary form only given. We report here the first observation of the Rabi nutation of an atom in vacuum and in controlled coherent fields. Atomic and cavity relaxations are small enough to permit the observation of four oscillation periods in vacuum and the resolution of several individual frequency components when a field is injected.