Probing a Bose-Einstein condensate with an atom laser

A pulsed atom laser derived from a Bose-Einstein condensate is used to probe a second target condensate. The target condensate scatters the incident atom laser pulse. From the spatial distribution of scattered atoms, one can infer important properties of the target condensate and its interaction with the probe pulse. As an example, we measure the s-wave scattering length that, in low energy collisions, describes the interaction between the |F = 1,mF = −1> and |F = 2,mF = 0> hyperfine ground states in 87Rb

Approaching the Heisenberg limit in an atom laser

We present experimental and theoretical results showing the improved beam quality and reduced divergence of an atom laser produced by an optical Raman transition, compared to one produced by an rf transition. We show that Raman outcoupling can eliminate the diverging lens effect that the condensate has on the outcoupled atoms. This substantially improves the beam quality of the atom laser, and the improvement may be greater than a factor of 10 for experiments with tight trapping potentials. We show that Raman outcoupling can produce atom lasers whose quality is only limited by the wave function shape of the condensate that produces them, typically a factor of 1.3 above the Heisenberg limit

Investigation and comparison of multi-state and two-state atom laser output-couplers

We investigate the spatial structure and temporal dynamics created in a Bose-Einstein condensate (BEC) by radio-frequency (RF) atom laser output-couplers using a one-dimensional mean-field model. We compare the behavior of a `pure' two-state atom laser to the multi-level systems demonstrated in laboratories. In particular, we investigate the peak homogeneous output flux, classical fluctuations in the beam and the onset of a bound state which shuts down the atom laser output.Comment: 9 pages, 8 figure

Semiclassical limits to the linewidth of an atom laser

We investigate the linewidth of a quasi-continuous atom laser within a semiclassical framework. In the high flux regime, the lasing mode can exhibit a number of undesirable features such as density fluctuations. We show that the output therefore has a complicated structure that can be somewhat simplified using Raman outcoupling methods and energy-momentum selection rules. In the weak outcoupling limit, we find that the linewidth of an atom laser is instantaneously Fourier limited, but, due to the energy `chirp' associated with the draining of a condensate, the long-term linewidth of an atom laser is equivalent to the chemical potential of the condensate source. We show that correctly sweeping the outcoupling frequency can recover the Fourier-limited linewidth.Comment: 9 Figure

Mastery learning in a large first year physics class

In 2009 we tried an experiment in our large core first year physics course: we introduced mastery learning. The basic idea behind mastery learning is that any student can learn anything well, but that it takes some students much longer than others. We should therefore let students proceed through a course at different speeds, while insisting that they totally master each section of the course before moving on. The students have to get over 80% in each homework assignment before they are allowed to take the next one. They are, however, allowed to take different versions of each assignment multiple times until they reach this threshold. At the end, the weaker students would have covered less content than the strong ones, but they should have fully understood whatever they did. In the laboratory component, the students were assessed in each experiment against a set of lab mastery goals. The students could pass the lab component only if they have mastered each of these goals at least once. Did it work? Logistically it worked very well, somewhat to our surprise. There were a number of striking unexpected benefits: students did more work, complained less about the workload, asked for help more often, and showed an improved ability to solve questions first time around. Gains in student conceptual understanding were much improved, but this may be due to other innovations introduced in the course. Examination performance, however, did not improve, even on the most basic material. Students could do the problems when given unlimited time and assistance from peers, but not in exam conditions

Optical collisions in crossed beams and Bose-Einstein condensation in a microtrap

Thèse en cotutelleOptical collisions are studied in a crossed beams experiment. Differential cross sections of K-Arcollisions are measured and are used to derive the repulsive parts of the XΣ and BΣ potentialcurves. The achieved accuracy has not been realized with scattering experiments before. A collisionenergy resolved analysis of the final state probes the relative population of the fine-structurestates K(4p1/2) and K(4p3/2) which depends on details of the outer part of the potentials. Calculationsfrom the determined potentials are in concordance with the experimental results. Therelative population of the Na fine-structure states after Na-N2 and Na-O2 collisions is determinedsimilarly. The results for N2 are in very good agreement with the theory. Differential cross sectionsof Ca-Ar optical collisions are measured for an asymptotically forbidden transition. Thespectral dependence of the signal intensity shows a characteristic maximum. The experimentaldata are in good agreement with ab initio calculations.Wires on a microchip create a magnetic trap that is used to obtain a Rb-87 Bose-Einstein condensate.The roughness of the magnetic potential is characterized by the measured density of a coldatom cloud. The measured roughness is compared to the roughness that is calculated from thegeometry of the microwire.Nous avons étudié les collisions assistées par la lumière entre deux jets atomiques croisés. Lessections efficaces différentielles de collisions K-Ar sont mesurées et utilisées pour calculer lesparties répulsives des potentiels XΣ et BΣ. La précision sur les potentiels ainsi obtenus n'avaitjamais été atteinte auparavant dans des expériences de diffusion. Une analyse de l'état final enfonction de l'énergie de collision nous permet de sonder la population relative entre les niveauxfins K(4p1/2) et K(4p3/2). Cette différence relative de population dépend en détail de la structureexterne des potentiels. Les calculs à partir des potentiels déterminés sont en accord avec nosrésultats expérimentaux. Nous avons également étudié la population relative entre les états finsd'atomes de sodium après des collisions Na-N2 et Na-O2. Les résultats pour N2 sont en très bonaccord avec la théorie. Nous avons mesuré les sections efficaces différentielles de collision pourdes collisions Ca-Ar assistées par la lumière pour une transition asymptotiquement interdite. Ladépendance spectrale de l'intensité du signal présente un maximum caractéristique. Les donnéesexpérimentales sont en bon accord avec des calculs ab initio.Nous avons utilisé des fils microfabriqués pour créer un potentiel magnétique dans lequel nousavons obtenu un condensat de Bose-Einstein de 87Rb. Nous avons caractérisé la rugosité du potentielmagnétique en mesurant le profil de densité d'un nuage d'atomes froids. Nous comparonsla rugosité mesurée avec la rugosité calculée par la géométrie du fil

Repulsive KAr potentials from differential optical collisions

Experimental differential cross sections for the optical collision process K(4s)2S + Ar + hv → K(4p)2P + Ar are reported. The characteristic interference structures are used to determine the repulsive parts of the KAr X2σ and B2σ potential curves by

Differential scattering study of asymptotically forbidden optical transitions in CaAr collisions

We have investigated the laser excitation of CaAr collision pairs in a molecular beam experiment with differential detection. The metastable Ca(4s3d)1D state is populated by a collision-assisted transition. Measurements of differential cross-sections ar

Fine-structure transitions in the exit channel of K + Ar optical collisions

We study K + Ar collisions by laser excitation of the collision pair in a differential scattering experiment. The relative population of the K(4p) 2P fine-structure sublevels reflects the nonadiabatic coupling in the convergence region of the interactio