Magneto-optical trapping of a diatomic molecule

• Published in: Nature (London) 2014-08, Vol.512 (7514), p.286-289
• Main Authors: Barry, J. F., McCarron, D. J., Norrgard, E. B., Steinecker, M. H., DeMille, D.
• Format: Article
• Language: English
• Subjects: 639/766/36/1121; 639/766/36/1125; Atomic properties; Atoms; Atoms & subatomic particles; Cooling; Diatomic molecules; Doppler effect; Electric properties; Gases; Humanities and Social Sciences; Lasers; letter; Magnetic properties; Methods; multidisciplinary; Optical properties; Particle physics; Physics; Quantum theory; Science; Strontium; Trapping
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature13634

Magneto-optical trapping is the standard method for laser cooling and confinement of atomic gases but now this technique has been demonstrated for the diatomic molecule strontium monofluoride, leading to the lowest temperature yet achieved by cooling a molecular gas. Diatomic molecules trapped in three dimensions In the past decade the use of laser cooling to cool atoms to temperatures close to absolute zero, and their subsequent confinement in magneto-optical traps, has enabled a broad range of applications, from new atomic clocks to novel types of quantum matter. Molecules present a different challenge because the complexity of their internal structure renders current magneto-optical trapping techniques ineffective. Here, Daniel McCarron and colleagues demonstrate the first realization of a magneto-optical trap for a diatomic molecule — they use strontium monofluoride — in a three-dimensional magneto-optical trap. The authors' method is an extension of magneto-optical traps for atoms, but it uses transitions that are rarely exploited for atomic traps. A trapped molecule is an ideal starting point for high-precision measurement of fundamental constants or for the study of chemistry at ultracold temperatures. Laser cooling and trapping are central to modern atomic physics. The most used technique in cold-atom physics is the magneto-optical trap (MOT), which combines laser cooling with a restoring force from radiation pressure. For a variety of atomic species, MOTs can capture and cool large numbers of particles to ultracold temperatures (less than ∼1 millikelvin); this has enabled advances in areas that range from optical clocks to the study of ultracold collisions, while also serving as the ubiquitous starting point for further cooling into the regime of quantum degeneracy. Magneto-optical trapping of molecules could provide a similarly powerful starting point for the study and manipulation of ultracold molecular gases. The additional degrees of freedom associated with the vibration and rotation of molecules, particularly their permanent electric dipole moments, allow a broad array of applications not possible with ultracold atoms 1 . Spurred by these ideas, a variety of methods has been developed to create ultracold molecules. Temperatures below 1 microkelvin have been demonstrated for diatomic molecules assembled from pre-cooled alkali atoms 2 , 3 , but for the wider range of species amenable to direct cooling and trapping, only recently have temperatur