Abstract
Complex molecular structure demands customized solutions to laser cooling by extending its general set of principles and practices. Compared with other laser-cooled molecules, yttrium monoxide (YO) exhibits a large electron-nucleus interaction, resulting in a dominant hyperfine interaction over the electron spin-rotation coupling. The YO ground state is thus comprised of two manifolds of closely spaced states, with one of them possessing a negligible Landé factor. This unique energy level structure favors dual-frequency dc magneto-optical trapping (MOT) and gray molasses cooling (GMC). We report exceptionally robust cooling of YO at over a wide range of laser intensity, detunings (one- and two-photon), and magnetic field. The magnetic insensitivity enables the spatial compression of the molecular cloud by alternating GMC and MOT under the continuous operation of the quadrupole magnetic field. A combination of these techniques produces a laser-cooled molecular sample with the highest phase space density in free space.
- Received 31 January 2020
- Revised 13 April 2020
- Accepted 21 April 2020
DOI:https://doi.org/10.1103/PhysRevX.10.021049
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Viewpoint
A New Way to Laser-Cool Molecules
Published 3 June 2020
Researchers exploit the peculiar structure of yttrium monoxide to cool the gas to ultralow temperatures and record-breaking densities.
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Popular Summary
Laser cooling of atoms has revolutionized modern physics. Extending this technique to molecules, however, has proven to be challenging due to the complexity of molecular structures. At the same time, this complexity could also lead to powerful applications in quantum chemistry, quantum information processing, and precision tests of fundamental physics. Here, we laser cool yttrium monoxide molecules to the lowest temperature of and achieve the highest (laser-cooled) molecular density.
We investigate a wide range of cooling and trapping strategies based on the unique energy level structure of yttrium monoxide, demonstrating efficient magneto-optical trapping and robust cooling to ultralow temperatures. We demonstrate that a particular mechanism of achieving extremely cold temperatures, known as gray molasses cooling, is exceptionally insensitive to magnetic fields for yttrium monoxide. This magnetic insensitivity enables us to compress the molecular cloud by applying the spring force associated with a magneto-optical trap to the ultracold sample under the continuous operation of a quadrupole magnetic field. With this method we find an order of magnitude increase in the phase-space density.
This ultracold and dense molecular sample can be readily loaded in an optical dipole trap and optical tweezer array for investigations of ultracold collisions, reactions, and quantum information processing.