Collisional Studies of Ultracold Ground-State NaCs Molecules*

High loss rates have been a persistent barrier for quantum many-body experiments with ultracold molecules. The formation of collisional tetramer complexes and their subsequent excitation via trap light has been postulated as the dominant loss mechanism for samples of ultracold molecules. For some molecules (RbCs, KRb), such complexes have been observed and their lifetimes are in accordance with RRKM theory, while for others (NaK, NaRb) attempts to detect the complexes have failed. Given the many open questions regarding complex formation and lifetimes, the investigation of new molecular species is of particular importance. We report on collisional studies of ultracold NaCs molecules. With the ability to study samples of NaCs molecules in the absence of trap light for extended periods of time, our data excludes (NaCs)₂ complex lifetimes below 100 ms, significantly longer than predicted by RRKM theory. We also study the temperature-dependence of molecule loss rates. Our investigation sheds light on the scattering properties of NaCs molecules and the validity of using statistical theories to describe the (NaCs)₂ complex.