Rovibrational Cooling of Molecules by Optical Pumping

Abstract

We demonstrate rotational and vibrational cooling of cesium dimers by optical pumping techniques. We use two laser sources exciting all the populated rovibrational states, except a target state that thus behaves like a dark state where molecules pile up thanks to absorption-spontaneous emission cycles. We are able to accumulate photoassociated cold Cs(2) molecules in their absolute ground state (v = 0, J = 0) with up to 40% efficiency. Given its simplicity, the method could be extended to other molecules and molecular beams. It also opens up general perspectives in laser cooling the external degrees of freedom of molecules.

Thermometry of Guided Molecular Beams from a Cryogenic Buffer‐Gas Cell

“…Cold molecules are also beneficial for precision spectroscopy, serving as an important tool for exploring fundamental physics [13,14,15]. For various applications of cold polar molecules, achieving high purity of and control over their internal states [16,17,18], in addition to having the ability to manipulate their motional behaviour [19,20,21,22,23,24,25,26,27], is of paramount importance. In pursuit of this goal, cryogenic buffer-gas cooling has proven to be a very general and powerful method to produce internally and translationally cold molecules [28,29,30].…”

Laser cooling of rotation and vibration by optical pumping

“…The main idea of the vibrational pumping demonstrated for Cs 2 molecules in [20,21,36,[41][42][43] and recently for NaCs molecules [24] consists in using a broadband laser tuned to the transitions between the different vibrational levels v X and the levels belonging to an electronically excited state, namely the B 1 Π u state in the cesium case. Starting from a given vibrational distribution of v X , the aim is to transfer it into a single target vibrational level.…”

“…Unfortunately, those molecules have a substantial residual internal energy because the decay of the electronically excited state used in the photo-association process generally leads to populate several vibrational and rotational levels. We have only recently achieved the transfer and the accumulation of molecules to a single rovibrational level of the electronic ground state [20,21]. The aim of this paper is to describe the basics of our method that is, in summary, based on a broadband and incoherent optical source designed to modify the distribution of the ro-vibrational populations.…”

Rotational Cooling of Trapped Polyatomic Molecules

“…Gaining quantum-state control of such molecules requires some form of internal-state cooling. While internal-state cooling has been demonstrated for bialkali dimers [16][17][18] as well as for a number of diatomic molecular ions [19][20][21][22][23], its implementation for polyatomic molecules is lacking.In this Letter, we demonstrate comprehensive internalstate control of the polyatomic molecule methyl fluoride (CH 3 F). In a two-step process, molecules in 16 rotational M -sublevels in the lowest four rotational J states in the |K|=3 manifold are optically pumped into a single rotational M -sublevel (J, K, M being the usual symmetrictop rotational quantum numbers).…”