Laser Cooling of Transition Metal Atoms

TL;DR

This paper explores laser cooling of transition-metal atoms, highlighting their unique atomic properties that enable ultra-low temperature cooling and proposing specific transitions for elements like titanium and others in various groups.

Contribution

It identifies suitable optical transitions in transition-metal atoms for laser cooling, expanding the scope beyond traditional alkali atoms.

Findings

Titanium's $a ^5F_5$ state supports a nearly closed optical transition.

Estimated leakage out of the transition is below 10^{-5}.

Optical transitions are proposed for multiple transition-metal groups.

Abstract

We propose the application of laser cooling to a number of transition-metal atoms, allowing numerous bosonic and fermionic atomic gases to be cooled to ultra-low temperatures. The non-zero electron orbital angular momentum of these atoms implies that strongly atom-state-dependent light-atom interactions occur even for light that is far-detuned from atomic transitions. At the same time, many transition-metal atoms have small magnetic dipole moments in their low-energy states, reducing the rate of dipolar-relaxation collisions. Altogether, these features provide compelling opportunities for future ultracold-atom research. Focusing on the case of atomic titanium, we identify the metastable $a ^5F_5$ state as supporting a $J \rightarrow J+1$ optical transition with properties similar to the D2 transition of alkali atoms, and suited for laser cooling. The high total angular momentum and electron spin of this state suppresses leakage out of the the nearly closed optical transition to a branching ratio estimated below $\sim 10^{-5}$. Following the pattern exemplified by titanium, we identify optical transitions that are suited for laser cooling of elements in the scandium group (Sc, Y, La), the titanium group (Ti, Zr), the vanadium group (V, Nb), the manganese group (Mn, Tc), and the iron group (Fe, Ru).