PUBLICATION: PHYSICAL REVIEW A

AUTHORS: Tang, RL; Si, R; Fei, ZJ; Fu, XX; Lu, YZ; Brage, T; Liu, HT; Chen, CY; Ning, CG

 

Despite the fact that the laser-cooling method is a well-established technique to obtain ultracold neutral atoms and atomic cations, it has rarely if ever been applied to atomic anions due to the lack of suitable electric-dipole transitions. Efforts of more than a decade have until recently only resulted in La- as a promising anion candidate for laser cooling, but our previous work [Tang et al., Phys. Rev. Lett. 123, 203002 (2019)] showed that Th- is also a potential candidate. Here we report on a combination of experimental and theoretical studies to determine the frequencies and rates, as well as branching ratios, for the relevant transitions in Th-. The resonant frequency of the laser-cooling transition is determined to be. = 123.455(30) THz [lambda = 2428.4(6) nm]. The transition rate is calculated as A = 1.17 x 10(4) s(-1). Since the branching fraction to dark states is negligible, 1.47 x 10(-10), this represents an ideal closed cycle in Th- for laser cooling. Furthermore, the zero nuclear spin of 232Th makes the cooling process possible in a Penning trap, which can be used to confine both antiprotons and Th- ions. The presented ion dynamics simulations show that the laser-cooled Th- anions can effectively cool antiprotons to a temperature around 10 mK.

 

LINKS: http://dx.doi.org/10.1103/PhysRevA.103.042817