The Dual Frequency Anisotropic Magneto-Optical Trap

The cloud of cold atoms produced by a Magneto-Optical Trap is known to exhibit instabilities. We examine in this paper in which limits it could be possible to realize an experimental trap similar to the configurations studied theoretically, i.e. mainly traps where one direction is privileged. We study the static behavior of an anisotropic trap, where anisotropy results essentially from the use of two different laser frequencies for the arms of the trap. Such a trap has very surprising behaviors, in particular the cloud disappears for some laser frequencies, while it exists for smaller and larger frequencies. A model is build to explain these behaviors. We show in particular that, to reproduce the experimental observations, the model has to take into account the cross saturation effects. Moreover, the couplings between the different directions cannot be neglected

Phase-space description of the magneto-optical trap

An exhaustive kinetic model for the atoms in a 1D Magneto-Optical Trap is derived, without any approximations. It is shown that the atomic density is described by a Vlasov-Fokker-Planck equation, coupled with two simple differential equations describing the trap beam propagation. The analogy of such a system with plasmas is discussed. This set of equations is then simplified through some approximations, and it is shown that corrective terms have to be added to the models usually used in this context

How to characterize the dynamics of cold atoms in non dissipative optical lattices?

We examine here the classical dynamics of cold atoms in square optical lattices, i.e. lattices obtained with two orthogonal stationary plane waves. Contrary to much of the past studies in this domain, the potential is here time independent and non dissipative. We show that, as a function of the experimental parameters, very different behaviors are obtained, both for the dynamics of atoms trapped inside individual sites, and for atoms travelling between sites: inside the sites, chaos may be a main regime or, on the contrary, may be negligible; outside the sites, chaos sometimes coexists with other regimes. We discuss what are the consequences of these differences on the macroscopic behavior of the atoms in the lattice, and we propose experimental measurements able to characterize these dynamics and to distinguish between the different cases

Online French Physical Society questionnaire: A way to identify students’ difficulties at the entrance at University

FRENCH CONTEXT In France, entry to university is determined by a national examination taken by all students in their final year at high school, the Baccalauréat (K12). Yet, its success rate (over 90%) no longer guarantees a satisfactory level of the laureates. French universities, where enrolment is (almost) free, are nevertheless legally obliged to accept all passed students. On leaving high school, other choices for students wishing to train in physics are to join either a preparatory school for engineering schools (CPGE), which is free for the most part, but is selective and includes intensive training, or a free and selective three-year professional course, or to enter university. The latest statistics show that only a small fraction of students who have followed a scientific course in high school choose to go to university (Inspection Générale - Ministry of National Education, 2022); scientific university tracks thus deal with students who are often already in difficulty and have to adapt their courses to help them succeed. Even if some universities have set up placement tests to organise support courses, there is no national system to monitor the evolution of students' levels and provide an overview. ONLINE PHYSICAL SOCIETY OF FRANCE QUESTIONNAIRE In this context, the French Physical Society has designed a one-hour online questionnaire (MCQ; Questionnaire de la Société Française de Physique, 2014) to help university teachers identify their students' difficulties. With four parts (basic mathematics, mechanics, waves and scientific culture) and around 100 questions, it can be completed in one hour and provides immediate feedback to students and their teachers on the answers provided. It also allows for the collection of data from all over the country. This MCQ, the content of which was chosen to comply with the high school curriculum (Ministry of National Education, 2019), consists primarily of questions on concepts, based on situations identified as likely to induce reasoning difficulties (Viennot, 1996) and is inspired by existing questionnaires (FCI, 1985 for example; Hestenes et al., 1992). Launched in 2014, this questionnaire was taken by more than 3000 students. It provides an admittedly partial view (but the only one available to our best knowledge) on the evolution of French students' understanding of concepts by the end of high school. We will present the results obtained by both CPGE classes and university students, and their evolution following the reform of the high school curriculum and the effects of COVID-19. While first analyses confirm the expected difference in level between the two populations, they also document, for both tracks, a significant decrease over time in the understanding of several concepts. REFERENCES Hestenes, D., Wells, M., & Swackhammer, G. (1992). Force Concept Inventory. The Physics Teacher, 30, 141. https://doi.org/10.1119/1.2343497 Inspection Générale - Ministry of National Education (2022). Presentation at the "Adaptation of higher education pathways to baccalaureate graduates resulting from the new reform of the physics curriculum" days. Nice, 2022. Ministry of National Education (2019). Programmes de Terminale en physique-chimie. Bulletin official n° 8, 2019 https://eduscol.education.fr/1648/programmes-et-ressources-en-physique-chimie-voie-gt [in French] Questionnaire de la Société Française de Physique (2014). http://qcm.sfpnet.fr/ Viennot, L. (1996). Reasoning in Physics: The Part of Common Sense. Springer

Dark Optical Lattice of Ring Traps for Cold Atoms

We propose a new geometry of optical lattice for cold atoms, namely a lattice made of a 1D stack of dark ring traps. It is obtained through the interference pattern of a standard Gaussian beam with a counter-propagating hollow beam obtained using a setup with two conical lenses. The traps of the resulting lattice are characterized by a high confinement and a filling rate much larger than unity, even if loaded with cold atoms from a MOT. We have implemented this system experimentally, and obtained a lattice of ring traps populated with typically 40 atoms per site with a life time of 30 ms. Applications in statistical physics, quantum computing and Bose-Einstein condensate dynamics are conceivable.Comment: 4 pages, submitted to PR

The Dynamical Regime of Sensory Cortex: Stable Dynamics around a Single Stimulus-Tuned Attractor Account for Patterns of Noise Variability.

Correlated variability in cortical activity is ubiquitously quenched following stimulus onset, in a stimulus-dependent manner. These modulations have been attributed to circuit dynamics involving either multiple stable states ("attractors") or chaotic activity. Here we show that a qualitatively different dynamical regime, involving fluctuations about a single, stimulus-driven attractor in a loosely balanced excitatory-inhibitory network (the stochastic "stabilized supralinear network"), best explains these modulations. Given the supralinear input/output functions of cortical neurons, increased stimulus drive strengthens effective network connectivity. This shifts the balance from interactions that amplify variability to suppressive inhibitory feedback, quenching correlated variability around more strongly driven steady states. Comparing to previously published and original data analyses, we show that this mechanism, unlike previous proposals, uniquely accounts for the spatial patterns and fast temporal dynamics of variability suppression. Specifying the cortical operating regime is key to understanding the computations underlying perception