Speaker
Description
Cold negative ions offer promising applications in areas such as quantum information science, fundamental physics, and chemistry. However, the cooling of these ions to temperatures near the Doppler limit has not yet been achieved.
Beyond ongoing work on the cooling of C$_2^-$, the boron nitride anion (BN$^-$) has emerged as a possible candidate ion for optical cycling and Doppler laser cooling. In our recent work [1], we investigated an optical cycling scheme for the Doppler cooling of cold, trapped $^{11}$B$^{14}$N$^-$ ions using excitation from the X$^2\Sigma^+$ ground state to the B$^2\Sigma^+$ excited state. Our results indicate that slow population decay via the first excited electronic state A$^2\Pi$ cannot be neglected. Consequently, various additional repump transitions, beyond what would be expected from the highly diagonal Franck Condon factor involving the B$^2\Sigma^+$($v$=0) $\leftarrow$ X$^2\Sigma^+$($v$=0) transition, must be excited to achieve efficient optical cycling. Furthermore, our findings indicate that the ions will likely need to be pre-cooled to translational temperatures near 1 K in order to reach a regime where Coulomb crystals are formed. For this reason, we have also performed extensive quantum calculations of potential energy curves for the interaction between BN$^-$ and the potential cryogenic buffer gases He and Ar.
In addition to these theoretical results, I will present experimental progress towards the spectroscopic characterization of laser cooling transitions in BN$^-$.
[1] K. Dulitz et al., Phys. Scripta, accepted (2025). DOI: https://doi.org/10.1088/1402-4896/adce43
