Kinetics of the evaporative cooling of an atomic beam

We compare two distincts models of evaporative cooling of a magnetically guided atomic beam: a continuous one, consisting in approximating the atomic distribution function by a truncated equilibrium distribution, and a discrete-step one, in which the evaporation process is described in terms of successive steps consisting in a truncation of the distribution followed by rethermalization. Calculations are performed for the semi-linear potential relevant for experiments. We show that it is possible to map one model onto the other, allowing us to infer, for the discrete-step model, the rethermalization kinetics, which turns out to be strongly dependent upon the shape of the confining potential.Comment: Submitted to Phys. Rev.

Experimental investigations of the dipolar interactions between single Rydberg atoms

This review summarizes experimental works performed over the last decade by several groups on the manipulation of a few individual interacting Rydberg atoms. These studies establish arrays of single Rydberg atoms as a promising platform for quantum state engineering, with potential applications to quantum metrology, quantum simulation and quantum information

Des atomes ultrafroids sous le microscope

Des atomes ultrafroids peuvent être piégés dans un réseau périodique obtenu à l’aide de faisceaux laser. De même que les électrons dans un solide, les atomes dans un tel « réseau optique » peuvent se comporter comme un métal supraconducteur ou au contraire comme un isolant. Les physiciens savent désormais observer ces phénomènes au microscope, atome par atome, avec une résolution comparable au pas du réseau. Ils peuvent aussi manipuler sélectivement les atomes d’un site donné, en changeant leur état quantique. Ces progrès ouvrent des perspectives enthousiasmantes pour le traitement quantique de l’information

Direct measurement of the van der Waals interaction between two Rydberg atoms

We report on the direct measurement of the van der Waals interaction between two isolated, single Rydberg atoms separated by a controlled distance of a few micrometers. By working in a regime where the single-atom Rabi frequency of the laser used for excitation to the Rydberg state is comparable to the interaction energy, we observe a \emph{partial} Rydberg blockade, whereby the time-dependent populations of the various two-atom states exhibit coherent oscillations with several frequencies. A quantitative comparison of the data with a simple model based on the optical Bloch equations allows us to extract the van der Waals energy, and to observe its characteristic $C_6/R^6$ dependence. The magnitude of the measured $C_6$ coefficient agrees well with an \emph{ab-initio} theoretical calculation, and we observe its dramatic increase with the principal quantum number $n$ of the Rydberg state. Our results not only allow to test an important physical law, but also demonstrate a degree of experimental control which opens new perspectives in quantum information processing and quantum simulation using long-range interactions between the atoms.Comment: 4 pages, 3 figures, published versio

Measurement of the Angular Dependence of the Dipole-Dipole Interaction Between Two Individual Rydberg Atoms at a F\"orster Resonance

We measure the angular dependence of the resonant dipole-dipole interaction between two individual Rydberg atoms with controlled relative positions. By applying a combination of static electric and magnetic fields on the atoms, we demonstrate the possibility to isolate a single interaction channel at a F\"orster resonance, that shows a well-defined angular dependence. We first identify spectroscopically the F\"orster resonance of choice and we then perform a direct measurement of the interaction strength between the two atoms as a function of the angle between the internuclear axis and the quantization axis. Our results show good agreement with the expected angular dependence $\propto(1-3\cos^2\theta)$, and represent an important step towards quantum state engineering in two-dimensional arrays of individual Rydberg atoms.Comment: 5 pages, 4 figure

Local optical control of the resonant dipole-dipole interaction between Rydberg atoms

We report on the local control of the transition frequency of a spin-$1/2$ encoded in two Rydberg levels of an individual atom by applying a state-selective light shift using an addressing beam. With this tool, we first study the spectrum of an elementary system of two spins, tuning it from a non-resonant to a resonant regime, where "bright" (superradiant) and "dark" (subradiant) states emerge. We observe the collective enhancement of the microwave coupling to the bright state. We then show that after preparing an initial single spin excitation and letting it hop due to the spin-exchange interaction, we can freeze the dynamics at will with the addressing laser, while preserving the coherence of the system. In the context of quantum simulation, this scheme opens exciting prospects for engineering inhomogeneous XY spin Hamiltonians or preparing spin-imbalanced initial states.Comment: 5 pages, 3 figure

A basic introduction to ultrastable optical cavities for laser stabilization

We give a simple introduction to the properties and use of ultrastable optical cavities, which are increasingly common in atomic and molecular physics laboratories for stabilizing the frequency of lasers to linewidths at the kHz level or below. Although the physics of Fabry-Perot interferometers is part of standard optics curricula, the specificities of ultrastable optical cavities, such as their high finesse, fixed length, and the need to operate under vacuum, can make their use appear relatively challenging to newcomers. Our aim in this work is to bridge the gap between generic knowledge about Fabry-Perot resonators and the specialized literature about ultrastable cavities. The intended audience includes students setting up an ultrastable cavity in a research laboratory for the first time and instructors designing advanced laboratory courses on optics and laser stabilization techniques.Comment: 10 pages, 8 figures, tutorial article to appear in Am. J . Phy

An atom-by-atom assembler of defect-free arbitrary 2d atomic arrays

Large arrays of individually controlled atoms trapped in optical tweezers are a very promising platform for quantum engineering applications. However, to date, only disordered arrays have been demonstrated, due to the non-deterministic loading of the traps. Here, we demonstrate the preparation of fully loaded, two-dimensional arrays of up to 50 microtraps each containing a single atom, and arranged in arbitrary geometries. Starting from initially larger, half-filled matrices of randomly loaded traps, we obtain user-defined target arrays at unit filling. This is achieved with a real-time control system and a moving optical tweezers that performs a sequence of rapid atom moves depending on the initial distribution of the atoms in the arrays. These results open exciting prospects for quantum engineering with neutral atoms in tunable geometries