An experimental and theoretical guide to strongly interacting Rydberg gases

We review experimental and theoretical tools to excite, study and understand strongly interacting Rydberg gases. The focus lies on the excitation of dense ultracold atomic samples close to, or within quantum degeneracy, to high lying Rydberg states. The major part is dedicated to highly excited S-states of Rubidium, which feature an isotropic van-der-Waals potential. Nevertheless, the setup and the methods presented are also applicable to other atomic species used in the field of laser cooling and atom trapping.Comment: 23 pages, 22 figures, tutoria

Lifetimes of ultralong-range Rydberg molecules in vibrational ground and excited state

Since their first experimental observation, ultralong-range Rydberg molecules consisting of a highly excited Rydberg atom and a ground state atom have attracted the interest in the field of ultracold chemistry. Especially the intriguing properties like size, polarizability and type of binding they inherit from the Rydberg atom are of interest. An open question in the field is the reduced lifetime of the molecules compared to the corresponding atomic Rydberg states. In this letter we present an experimental study on the lifetimes of the ^3\Sigma (5s-35s) molecule in its vibrational ground state and in an excited state. We show that the lifetimes depends on the density of ground state atoms and that this can be described in the frame of a classical scattering between the molecules and ground state atoms. We also find that the excited molecular state has an even more reduced lifetime compared to the ground state which can be attributed to an inward penetration of the bound atomic pair due to imperfect quantum reflection that takes place in the special shape of the molecular potential

Wechselwirkende Rydberg-Atome : Kohärente Kontrolle an Förster-Resonanzen und polare, homonukleare Moleküle

Interactions between single atoms are fundamental to physics and to control them is an ultimate goal. The exaggerated properties of Rydberg atoms offer to met the technical challenges to isolate and control single interaction channels in ultracold gases. Here, I present experiments on two subjects related to interactions of Rydberg atoms in dense ultracold clouds. One subject concerns coherence in strongly interacting ensembles of atoms, where the interaction between Rydberg atoms is induced via Stark-tuned Förster resonances. Pulsed experiments, following the idea of Ramsey experiments, are used for high resolution spectroscopy of the Förster defect and phase sensitive detection. Coherent oscillations between pair states and an interaction-induced phase shift of Rydberg atoms are measured. These experiments are accompanied by calculations of the interaction strength and by simulations using the concept of a pair state interferometer. The simulations nicely reproduce the experimental findings and support the observation that the ensemble of atoms in the presence of interactions can be described and controlled coherently. The second subject of this thesis is the measurement of a permanent dipole moment in a homonuclear diatomic molecule that arises by the interaction between a Rydberg atom and a ground state atom. Usually parity symmetry prohibits a permanent dipole moment in diatomic molecules, but here the strong asymmetry between the constituents of the ultralong-range Rydberg molecule allows breaking parity symmetry. These molecules consist of one ground state atom bound inside the Rydberg electron wavefunction of a highly excited atom. Calculations predict dipole moments on the order of 1 Debye. Experimental proof is reported on the measurement of a linear Stark effect of these molecules, in excellent agreement with the calculations.Ein fundamentaler Teil der Physik sind Wechselwirkungen, nicht nur in Hinblick darauf sie zu verstehen, sondern auch darauf sie zu kontrollieren. Die ungewöhnlichen Eigenschaften von Rydberg Atomen bieten die Möglichkeit, einzelne Wechselwirkungsmechanismen in ultrakalten Gasen zu isolieren und zu kontrollieren. Hier stelle ich Experimente auf dem Gebiet der stark wechselwirkenden Rydberg Atomen vor. Ein Teil untersucht die Kohärenz in stark wechselwirkenden Ensembles von ultrakalten Atomen, deren Wechselwirkung durch Förster Resonanzen in elektrischen Feldern induziert werden. Ähnlich einer Ramsey Sequenz werden gepulste Experimente genutzt um den Förster Defekt in einer phasensensitiven, hochauflösenden Spektroskopie zu messen. Desweiteren werden kohärente Oszillationen und wechselwirkungsinduzierte Phasenverschiebungen nachgewiesen. Berechnungen der Wechselwirkungsstärke und Simulationen der Experimente auf Basis eines Paarzustands-Interferometers reproduzieren die experimentellen Ergebnisse sehr gut. Diese Übereinstimmung unterstützt die Beobachtung, dass ein Ensemble von Atomen mit starken Wechselwirkungen kohärent kontrolliert und beschrieben werden kann. Der zweite Teil dieser Arbeit handelt von Messungen eines permanenten Dipolmomentes in einem homonuklearen Molekül, das durch die Wechselwirkung zwischen einem Rydberg Atom und einem Atom im Grundzustand gebunden ist. Üblicherweise tritt ein solches Dipolmoment in zweiatomaren Molekülen nicht auf, weil es aufgrund von Paritätssymmetrie verboten ist. Hier hingegen bricht die starke Asymmetrie der Konstituenten des langreichweitigen Rydbergmoleküls die Paritätssymmetrie. Berechnungen lassen ein Dipolmoment von etwa 1 Debye erwarten. Der experimentelle Nachweis dieses Dipolmomentes gelang durch die Messung eines linearen Stark-Effektes der Moleküle, in hervorragender Übereinstimmung mit den theoretischen Vorhersagen