UvA-DARE (Digital Academic Repository) Ultracold RbSr Optical and magnetic spectroscopy, Feshbach resonances and molecular structure Barbé, V.P.J. Link to publication License Other Citation for published version (APA): Barbé, V. P. J. (2021). Ultracold RbSr: Optical and magnetic spectroscopy, Feshbach resonances and molecular structure. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. UvA-DARE is a service provided by the library of the University of Amsterdam (http://dare.uva.nl) Download date: 22 Feb 2021 Ultracold RbSr: Optical and magnetic spectroscopy, Feshbach resonances and molecular structure Vincent Barbé Van der Waals-Zeeman Institute, Institute of Physics University of Amsterdam A thesis submitted for the degree of Doctor of Philosophy September 2020 Ultracold RbSr: Optical and magnetic spectroscopy, Feshbach resonances and molecular structure ACADEMISCH PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Universiteit van Amsterdam op gezag van de Rector Magnificus prof. dr. ir. K.I.J. Maex ten overstaan van een door het College voor Promoties ingestelde commissie, in het openbaar te verdedigen in de Agnietenkapel op woensdag 24 februari 2021, te 10.00 uur door Vincent Philippe Jean Barbé geboren te La Roche-Sur-Yon Promotiecommissie Promotor: prof. dr. F.E. Schreck Universiteit van Amsterdam Copromotor: dr. B.B. Pasquiou Universiteit van Amsterdam Overige leden: prof. dr. S. Ospelkaus-Schwarzer Leibniz Universität Hannover prof. dr. ir. G.C. Groenenboom Radboud Universiteit Nijmegen prof. dr. J.T.M. Walraven Universiteit van Amsterdam prof. dr. ir. H.B. van Linden van Universiteit van Amsterdam den Heuvell dr. R. Gerritsma Universiteit van Amsterdam Faculteit der Natuurwetenschappen, Wiskunde en Informatica iii The research reported in this thesis was carried out at the Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam. The research for/publication of this doc- toral thesis received financial assistance from the Netherlands Organisation for Scientific Research (NWO) through the Programme grant No. 680.92.18.05, Quantum Simulation 2.0 and the Vici grant No. 680-47-619, and from the European Research Council (ERC) under the European Union’s Seventh Framework Programme (FP7/2007-2013) (Grant agreement No. 615117 QuantStro). v À mon père et ma mère. vii Summary Atoms and molecules are the constituents of the material world. The binding of atoms into diatomic and polyatomic molecules is the basis of all chemistry, and renders possible the emergence of stars and galaxies, atmospheres and oceans, DNA and proteins. The last decades have witnessed the rapid development of experimental methods for the study of atoms and molecules at the microscopic level. Manipulating individual particles and individual quantum states has become possible, a physicist’s dream once thought to be delusional. The development of laser light sources in the second half of the 20st century, followed by their application to the cooling and trapping of particles, has permitted the cre- ation of highly quantum-degenerate gases of atoms in the form of Bose-Einstein condensates and Fermi seas, and the extensive study of their properties. Molecules, on the other hand, have proven more stubborn. Harder to cool down, harder to control at high densities, they come with a body of complexity that makes them both extremely appealing and very diffi- cult objects of study. To this date, only a handful of experimental groups in the world have obtained gases of diatomic molecules, the simplest form of all molecules, in the quantum- degenerate regime. This thesis reports on the experimental investigation of the RbSr molecule, which is a strongly polar, open-shell molecule. Such molecules are the subject of intense and ongo- ing experimental interest around the world, but have never been brought to the quantum- degenerate regime thus far. Hopefully, the methods and results presented in this thesis will lead to a change of this situation in the future. Two major results led to peer-reviewed publications in the context of this PhD thesis. The first is the experimental observation of magnetic Feshbach resonances between alkali and closed-shell atoms, never achieved before. This result opens the door to the magnetic asso- ciation of atom pairs into molecules of a new kind, among them RbSr, that have never been produced in the laboratory due to a lack of known magnetic resonances. The second major result is the understanding of the potential energy curve of ground-state RbSr, an achieve- ment of high importance for our future research. Based on this potential energy curve, we could predict the collisional properties of Rb-Sr mixtures of any isotopic combination, the binding energies of all molecular states in the electronic ground state and the position of viii yet-unobserved Feshbach resonances. In addition, an extensive part of my PhD was dedi- cated to the exploration of electronically-excited potential energy curves of RbSr. The results of this work are subject to an ongoing theoretical analysis, which will be published in the future. The last years of my PhD have been dedicated to the implementation of experimen- tal methods for the production and loading of cold Rb-Sr gases in an optical lattice, and to the implementation and characterization of a magnetic field stabilization system for RbSr magnetoassociation. This work is subject to ongoing development and improvement in the laboratory and I will discuss it succinctly in the outlook of this thesis. This manuscript serves two purposes. First, it will give the general and specialized reader a state-of-the-art account of the properties, applications and methods of formation of ultracold RbSr molecules. Second, it will present the theoretical and experimental con- cepts that underlie my PhD work in the RbSr laboratory. I have tried to synthetize in a clear and exhaustive manner the knowledge I have accumulated throughout the years, so that those who will come after me can rely upon it. The rotational and vibrational structure of RbSr is discussed in depth, along with the spectroscopy methods that I have used to explore it. The physics of Feshbach resonances in ultracold atom experiments is covered extensively, with particular attention given to bi-alkali resonances and resonances between alkali and closed-shell atoms, such as those I have observed in RbSr. From this knowledge I hope that new results and new ideas will emerge, for science is a long and unpredictable road. ix Samenvatting Atomen en moleculen zijn de bestanddelen van de materiële wereld. De verbinding van atomen in twee-atomige en meeratomige moleculen is de basis van alle chemie, en maakt het ontstaan mogelijk van sterren en sterrenstelsels, atmosferen en oceanen, DNA en proteïnen. De laatste decennia zijn we getuige geweest van een snelle ontwikkeling van experi- mentele methodes om atomen en moleculen op microscopisch niveau te bestuderen. Het is mogelijk geworden om individuele deeltjes en kwantumtoestanden te manipuleren – voor natuurkundigen een droom die ooit een waanvoorstelling leek. De ontwikkeling van laser- lichtbronnen in de tweede helft van de twintigste eeuw, gevolgd door hun toepassing bij het koelen en insluiten van deeltjes, heeft het mogelijk gemaakt kwantum-ontaarde gassen uit atomen te verkrijgen in de vorm van Bose-Einsteincondensaten en Fermi-zeeën, en hun eigenschappen uitgebreid te bestuderen. Moleculen hebben daarentegen bewezen koppiger te zijn. Aangezien ze moeilijker zijn af te koelen en bij hoge dichtheden lastiger te beheersen, gaan ze gepaard met een complexiteit die ze tegelijkertijd extreem aantrekkelijk en erg lastig maakt om te bestuderen. Tot op de dag van vandaag hebben slechts een handjevol experi- mentele groepen in de wereld gassen verkregen uit twee-atomige moleculen, het eenvoudig- ste type moleculen in het kwantum-ontaarde regime. Dit proefschrift doet verslag van het experimenteel onderzoek aan het RbSr-molecuul, een sterk polair open-shell molecuul. Zulke moleculen zijn over de hele wereld het onder- werp van intense en voortdurende experimentele interesse, maar zijn tot dusver nooit naar het kwantum-ontaarde regime gebracht. Hopelijk brengen de methoden en resultaten die in dit manuscript worden gepresenteerd in de toekomst verandering in deze situatie. Twee belangrijke resultaten leidden in de context van dit proefschrift tot peer-reviewed publicaties. Het eerste was de experimentele waarneming van magnetische Feshbach-reso- nanties tussen alkali-atomen en aardalkali-atomen, wat nooit eerder was gelukt. Dit resul- taat opent de deur voor de magnetische associatie van paren van atomen tot moleculen van een nieuw type, waaronder RbSr, die nooit in het laboratorium zijn geproduceerd vanwege een gebrek aan bekende magnetische