Rovibrational Optical Pumping of NaCs

We demonstrate efficient cooling of the rotational degree of freedom of ultracold NaCs molecules through narrow line optical pumping. Molecules in v''=0, N''=2 and 4 are excited to the lowest vibrational level of the $A^1\Sigma^+-b^3\Pi$ complex from which they decay to v''=0, N''=0. We achieve cooling of both rotational and vibrational degrees of freedom by applying this technique in conjunction with broadband optical pumping [1]. This technique also allows transfer of population between any of the lowest vibrational states (v''=0-2) at kHz rates.\\[4pt] [1] D. Sofikitis, R. Horchani, X. Li, M. Pichler, M. Allegrini, A. Fioretti, D. Comparat, and P. Pillet, Phys. Rev. A 80, 051401(R) (2009)