Laser cooling and trapping of neutral particles, first proposed around fifty years ago, led to a revolution in atomic physics that now underpins a wide range of new scientific tools and technologies. Much of the periodic table can be trapped at microkelvin temperatures (0.000001 °C above absolute zero) in vacuum, which is much colder than anywhere else in the observable universe. Applying the same tools to even the simplest chemical compounds (e.g. diatomic molecules) is much more difficult, and until now has only worked for a handful of reactive molecules having an unpaired electron.
This thesis demonstrates trapping of aluminum monofluoride (AlF). AlF is a closed shell molecule with a deeply-bound electronic ground state, and is remarkably unreactive at very low temperatures. It is shown here that AlF can be decelerated and trapped using deep ultraviolet light (wavelength 227.5 nm). About 60,000 AlF molecules in the first excited rotational level are trapped at a temperature around 15 millikelvin, and for the first time, this trapping is extended higher up the ladder of rotational levels. Cooling of such a stable species to ultracold temperatures will enhance studies of strongly interacting quantum systems and similar experiments on prototypical quantum computers.
J. Eduardo Padilla-Castillo completed his BSc in Physics at the National Autonomous University of Mexico (UNAM) in 2017. He subsequently obtained his MSc in Physics from the Physics Institute at UNAM in 2021. During his MSc, he undertook research into ultracold atomic gases composed of lithium atoms in the Ultracold Matter Laboratory at UNAM. This work resulted in the first molecular Bose-Einstein condensate in Latin America. As a PhD candidate in the Molecular Physics department at the Fritz Haber Institute (Max Planck Society), his research focused on spectroscopy and laser-cooling techniques with deep ultraviolet light. In 2025, Eduardo and colleagues achieved magneto-optical trapping of aluminum monofluoride, a uniquely stable laser-coolable molecule and the first of its kind to be trapped. Eduardo currently works as postdoctoral researcher in the same laboratory, where he continues research on AlF, aiming to push the experiment towards colder temperatures.