Small Diatomic Alkali Molecules at Ultracold Temperatures

This thesis describes experimental work done with two of the smallest diatomic alkali molecules, 6Li2 and 23Na6Li, each formed out of its constituent atoms at ultracold temperatures. The 23Na6Li molecule was formed for the first time at ultracold temperatures, after previous attempts failed due to an incorrect assignment of Feshbach resonances in the 6Li+23Na system. The experiment represents successful molecule formation around the most difficult Feshbach resonance ever used, and opens up the possibility of transferring NaLi to its spin-triplet ground state, which has both magnetic and electric dipole moments and is expected to be long-lived. For 6Li2, the experimental efforts in this thesis have solved a long-standing puzzle of apparently long lifetimes of closed-channel fermion pairs around a narrow Feshbach resonance, finding that the lifetime is in fact short, as expected in the absence of Pauli suppression of collisions. Moreover, measurements of collisions of Li2 with free Li atoms demonstrates a striking first example of collisions involving molecules at ultracold temperatures described by physics beyond universal long-range van der Waals interactions

Deviation from Universality in Collisions of Ultracold [superscript 6] Li[subscript 2] Molecules

Collisions of [superscript 6]Li[subscript 2] molecules with free [superscript 6]Li atoms reveal a striking deviation from universal predictions based on long-range van der Waals interactions. Li[subscript 2] closed-channel molecules are formed in the highest vibrational state near a narrow Feshbach resonance and decay via two-body collisions with Li[subscript 2], Li, and Na. For Li[subscript 2]+Li[subscript 2] and Li[subscript 2]+Na, the decay rates agree with the universal predictions of the quantum Langevin model. In contrast, the rate for Li[subscript 2]+Li is exceptionally small, with an upper bound 10 times smaller than the universal prediction. This can be explained by the low density of available decay states in systems of light atoms [G. Quéméner, J.-M. Launay, and P. Honvault, Phys. Rev. A 75 050701 (2007)], for which such collisions have not been studied before.United States. Air Force Office of Scientific Research. Multidisciplinary University Research InitiativeUnited States. Army Research Office. Multidisciplinary University Research InitiativeNational Science Foundation (U.S.)United States. Office of Naval ResearchUnited States. Army Research Office (Grant W911NF-07-1-0493)United States. Defense Advanced Research Projects Agency. Optical Lattice Emulator ProgramNatural Sciences and Engineering Research Council of Canad