Cold atoms and molecules have been used as platforms for a variety of applications, including quantum computation, quantum simulation, and precision measurements. Techniques to cool atoms have been perfected over the last decades, but there exist many additional challenges for molecules.
Molecules have a complex internal structure: they have rotational, electronic and vibrational degrees of freedom. Therefore, in contrast to alkali atoms, it is very hard to find closed cycling transitions laser cooling can be applied to. In order to extend developed laser cooling techniques to molecules, we use photoassociation: we pre-cool Rubidium (Rb) and Cesium (Cs) atoms first and then associate pairs of them with a laser to create ultracold (~100uK) diatomic (RbCs) molecules. Recently we discovered that photoassociation is capable of producing molecules in the electronic, vibrational, and rotaional ground state. Such molecules in their ground state are practically important because they do not have excess energy that can be converted to kinetic energy. This is an important step toward preparing molecules in an optical trap, which can be used for further applications.