Single-photon molecular cooling

Abstract

We propose a general method to cool the translational motion of molecules. Our method is an extension of single photon atomic cooling which was successfully implemented in our laboratory. Requiring a single event of absorption followed by a spontaneous emission, this method circumvents the need for a cycling transition and can be applied to any paramagnetic or polar molecule. In our approach, trapped molecules would be captured near their classical turning points in an optical dipole or RF-trap following an irreversible transition process.Cooling the translational motion of molecules has been one of the grand challenges of physics and chemistry for many years, motivated by the wide range of fundamental problems that could be addressed. For example, the study of chemical reactions at ultra low temperatures would open a new and unexplored regime of cold chemistry, where reactions might proceed through resonance states [1] and the reaction rate and outcome could be controlled by externally applied fields [2]. Cold molecules would enable precision molecular spectroscopy, possibly allowing the observation of a variation in time of the fundamental constants [3-5]. Ultimately, cooling of molecules could enable the study of quantum degenerate polar molecular gases [6,7]. The established methods of molecular cooling work down to a temperature of tens to hundreds of mK. These include cooling by collisions with a cold buffer gas either in a cryogenic cell or during an adiabatic (supersonic) expansion. Buffer gas cooled paramagnetic molecules have been magnetically trapped [8] whereas cold supersonic molecular beams have to be first decelerated to trapping velocities by interaction with time dependent electric [9-11] or magnetic fields [12-16].To reach lower temperatures and higher phase space densities, a different method must be used. A natural candidate is evaporative cooling, however this method is not likely to work for molecules in a lowfield seeking state due to inelastic collisions. Application of standard laser cooling to molecules has been investigated by Di Rosa [17], however the method is not general due to the complicated internal structure.More general cooling methods have been suggested, including cavity cooling [18,19] and the ``optical shaker'' [20].A new approach, single-photon cooling, was recently proposed and demonstrated by us for magnetically trapped atoms [21,22]. We show in this Letter that this method can be naturally extended to molecules. We start with an example of a straightforward application of the single photon cooling technique on a molecular radical and propose a new

Ultracold O2 + O2 collisions in a magnetic field: On the role of the potential energy surface

“…For paramagnetic molecules, a magnetic trap is used since molecules in a low-field-seeking state [12] (lfs) are trappable provided that their translational energy is lower than the trap depth [13]. This situation could be achieved by direct cooling methods such as Zeeman slowing [14], optical Stark deceleration [15], single-photon cooling [16] or sympathetic cooling [17]. It might also be possible to cool the molecules towards the ultracold regime by evaporative cooling [18].…”

An experimental test of the weak equivalence principle for antihydrogen at the future FLAIR facility

“…35 A new version of singlephoton cooling is an all-magnetic approach with dressed RF states and a single laser beam to induce the irreversible step. 36 This version will enable trapping of nearly all the atoms, limited only by the branching ratio of the spontaneous emitted photons (around 50%). This method should work well on hydrogen and antihydrogen.…”

Decelerating and Trapping Large Polar Molecules

“…[9].O ther proposed and demonstrated methods form anipulating larger molecules include deceleration through pulsed optical forces [10] and pulsed Zeemand eceleration of molecules and polyatomic radicals. [11,12] Trapping larger,n eutral molecules remains am ajor goal of the cold molecule community.…”