Quantum-Degenerate Straontium: Mixtures, Molecules and Many-Body Physics

Quantum mechanics governs the world on the microscopic scale and gives rise to phenomena not known to classical physics. Understanding these phenomena, especially the ones emerging from the interaction of many quantum particles, will not only deepen our knowledge of nature, but also inspire the creation of materials with unheard of, useful properties or enable the construction of novel quantum devices. Even though the fundamental laws of quantum mechanics are known, it is often extremely difficult or even impossible to calculate the properties of a quantum system. Therefore experiments are required to test and push the boundaries of our understanding. During the first stage of this START project, ultracold strontium gases were established as new, well-controlled quantum systems, which serve to explore new regimes of quantum mechanics and to build unique, very useful quantum devices. We developed methods that cool gases of all strontium isotopes and their mixtures to extremely low temperature and give us full control over these gases. During this work an unforeseen opportunity arose to solve a long-standing, big challenge in our field, the production of a gas in the quantum regime using only a single cooling technique. Our new method also overcomes the crucial challenges that have so far hindered the creation of a perpetual atom laser. In the coming years we will leverage our unique know-how and build such a quantum device. This atom laser will be perfectly suited to improve precision measurement devices, such as clocks or accelerometers, which have important applications, e.g. for navigation, geology, or to search for changes over time in the fundamental constants of nature. The second stage of our project was dedicated to the creation of RbSr molecules with full control over all degrees of freedom. These molecules have unique features, a long-range electric dipole interaction and an unpaired electron. These features will enable us to study even richer quantum-many body systems than using the much simpler Sr atoms. We have extended our machine with Rb, created a Rb-Sr gas mixture in the quantum regime, and spectroscopically characterized relevant RbSr properties. We also devised a new molecule creation method, suitable for RbSr, and tested it by creating Sr2 molecules. The success of my START project has enabled me to obtain a full professorship position at the University of Amsterdam in 2013, just three years after the beginning of the project. My group and the Rb-Sr experiment has moved from Innsbruck to Amsterdam, where we will continue our research, funded by an ERC consolidator grant.