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Deceleration and trapping of cold free radicals


Since the realization of Bose-Einstein condensation (BEC) of ultracold atoms, experimental observation of correlated motion of matter waves of particles in an ensemble has drawn considerable attention in various fields, revealing new quantum aspects of matter. Especially, the research of cold and ultracold molecules has expanded rapidly over the past decade because of their importance in various fields from fundamental physics to interstellar chemistry.  Recently we have demonstrated that a supersonic beam of methyl radical (CH3), one of the most important hydrocarbon free radicals, has been slowed down to standstill with a magnetic molecular decelerator, and successfully captured spatially in an anti-Helmholtz magnetic trap for over 1 s. [PRL, 118, 093201 (2017), also Physics Today, 70, 4, 18(2017)] The present method is, in general, applicable to trap any molecule (or atom) that has one or more unpaired electrons, i.e. free radicals. The demonstrated trapping capability of polyatomic radicals opens up various possibilities for realizing ultracold ensembles of molecules towards Bose-Einstein condensation of polyatomic molecules, investigations of reactions governed by quantum statistics, and applications to quantum information processes. Furthermore, high-resolution spectroscopy of trapped cold radicals may reveal parity violation in molecules, which might be related to the homochirality of biological molecules. We will discuss the details of our experiments and various future applications of trapped free radicals.