title: Rotational Cooling of Trapped Polyatomic Molecules.
abstract: Controlling the internal degrees of freedom is a key challenge for applications of cold and ultracold molecules. Here, we demonstrate rotational-state cooling of trapped methyl fluoride molecules (CH_{3}F) by optically pumping the population of 16 M sublevels in the rotational states J=3, 4, 5 and 6 into a single level. By combining rotational-state cooling with motional cooling, we increase the relative number of molecules in the state J=4, K=3, M=4 from a few percent to over 70%, thereby generating a translationally cold (≈30  mK) and nearly pure state ensemble of about 10^{6} molecules. Our scheme is extendable to larger sets of initial states, other final states, and a variety of molecule species, thus paving the way for internal-state control of ever-larger molecules.
authors.affiliation: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, D-85748 Garching, Germany.
authors.forename: Rosa
authors.initials: R
authors.lastname: Glöckner
authors.affiliation: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, D-85748 Garching, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Prehn
authors.affiliation: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, D-85748 Garching, Germany.
authors.forename: Barbara G U
authors.initials: BG
authors.lastname: Englert
authors.affiliation: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, D-85748 Garching, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Rempe
authors.affiliation: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, D-85748 Garching, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Zeppenfeld