Progress towards new atomic species laser cooling

Jamie Shaw, L. Railing, Daniel McCarron

幹旺 上妻, Mikio Kozuma

Tao Chen, Bo Yan

Different from atoms, molecules have unique properties, and play an important role in the research of atomic, molecular and optical physics. Cold molecules have important applications in science and have been studied for more than 20 years. But traditional methods, such as the Stark decelerator, have hit a bottleneck: it is hard to increase the phase space density of molecules. Extending the direct laser-cooling technique to new molecular species has recently been a hot topic and also a big challenge. In this review paper, on one hand, we make a brief review to recent progresses on the direct laser cooling of polar molecules. On the other hand, a demonstration on the feasibility of laser cooling BaF molecule has been experimentally illustrated, including the analysis on the molecular energy levels, measurements of the high-resolution spectroscopy, efficient pre-cooling and state preparation via buffer-gas cooling and detailed investigations on the molcule-light interactions. All these results not only pave the way for future laser-cooling and -trapping experiments, but also serve as a reference for the laser-cooling explorations on new molecular species.

Daniel McCarron

Abstract The extension of laser cooling and trapping techniques from atoms to molecules is currently the subject of intense and growing interest. Molecular laser cooling and trapping offers a general technique applicable to a variety of molecules with different properties and internal structures and is well-suited to the growing list of proposed applications for ultracold molecules. The recent development of optical cycling schemes for specific molecular species now allow each molecule to scatter up to ∼10 6 photons. This has proven sufficient for multiple groups to laser cool and slow molecular beams and, notably, capture molecules in magneto-optical traps (MOTs) and cool them to ultracold temperatures. MOTs are the workhorse technique for atomic physics in the ultracold regime and today’s molecular MOTs represent a powerful starting point for the study and manipulation of ultracold molecular gases. This Topical Review presents a summary of the progress made in this new and emerging field.

Michael D. Di Rosa, Alexey Tonyushkin

Chun-Chia Chen, Shayne Bennetts, Rodrigo González Escudero +2 more

Leading tests of the Standard Model, like measurements of the electron electric dipole moment or of matter-antimatter asymmetry, are built upon our ability to laser-cool atoms and molecules to ultracold temperatures. Unfortunately, laser-cooling remains limited to a minute collection of species with very specific electronic structures. To include more species, such as polyatomic molecules or exotic atoms like antihydrogen, new cooling methods are needed. Here we demonstrate a method based on Sisyphus cooling that was proposed for laser-cooling antihydrogen. In our implementation, atoms are selectively excited to an electronic state whose energy is spatially modulated by an optical lattice, and the ensuing spontaneous decay completes one Sisyphus cycle. We show that this method eliminates many constraints of traditional radiation-pressure-based approaches, while providing similar atom numbers with lower temperatures. This laser-cooling method can be instrumental in bringing new exotic species and molecules to the ultracold regime.