Trapping a Precursor to Ultracold Hydrogen
As the simplest atom, hydrogen’s energy levels can be calculated to a higher precision than any other element. Comparing those predictions to spectroscopic measurements could allow researchers to test fundamental theories and to pin down the values of the physical constants. However, experimentalists have not yet been able to slow and isolate hydrogen atoms via laser cooling and trapping, the standard techniques for precision atomic measurement. Now Jinyu Dai of Columbia University and colleagues have taken a step toward confining atomic hydrogen at the necessary ultracold temperatures by laser cooling and trapping molecules of calcium monohydride [1]. Previous work suggested that the bond between the calcium and hydrogen in these molecules can be broken to produce ultracold hydrogen [2]. In addition, precision spectroscopy of calcium monohydride itself is relevant to astrophysics, as the molecule is found in stellar and interstellar media.
The researchers’ key achievement was to trap cold calcium monohydride in quantities large enough to study. Such quantities have previously been difficult to obtain because the molecules break apart via a process called predissociation. To minimize this breakup, Dai and colleagues devised a laser-cooling scheme that puts the calcium monohydride in an electronic state that is less prone to predissociation. They also broadened the frequency range of the cooling lasers, which allowed them to confine more calcium monohydride molecules by slowing particles moving at a larger range of speeds. In future work, the researchers plan to trap calcium monohydride molecules at higher densities and, by breaking the bonds in the molecules, isolate ultracold hydrogen atoms.
–Sophia Chen
Sophia Chen is a freelance science writer based in Columbus, Ohio.
References
- J. Dai et al., “Magneto-optical trapping of a metal hydride molecule,” Phys. Rev. Lett. 136, 233403 (2026).
- Q. Sun et al., “Probing the limits of optical cycling in a predissociative diatomic molecule,” Phys. Rev. Res. 5, 043070 (2023).