Researchers in Singapore have used a magneto-optical trap (MOT) to cool atoms in “main group III” of the periodic table to millikelvin temperatures. This group comprises boron and the elements below it in the table. The experiment is a first because these atoms do not have the right atomic properties for conventional MOT cooling. Travis Nicholson and colleagues at the National University of Singapore got around this problem by doing laser cooling on a metastable state of indium-115 atoms. Their approach could open new areas of the periodic table to ultracold-atom experiments that explore the quantum properties of matter.
By cooling atomic gases to near absolute zero temperature, physicists have unlocked a diverse array of fascinating phenomena and practical devices: including exotic states of matter; atomic clocks; and quantum sensors. In many of these experiments, the MOT is key to reaching cold temperatures. It works by confining an atomic gas using a spatially varying magnetic field. Laser beams are used to cool the gas – which counterintuitively involves exciting atoms out of their ground state.
So far, this cooling technique has been applied almost exclusively to alkali and alkaline-earth metals. As for most other elements, atomic transitions out of their ground states are not compatible with the operation of a MOT. While more complicated cooling schemes can sometimes be used, most of the periodic table remains unexplored at ultracold temperatures.
Long-lived metastable state
Instead of using a ground-state transition, Nicholson’s team used a transition from a long-lived metastable state in indium-115. To make use of this metastable state, the team had to design their MOT especially for this atom.
Ions and atoms react in magneto-optical trap
Having optimized their setup, Nicholson and colleagues loaded load half a billion indium-115 atoms into their MOT and were then able to cool them down to temperatures of about 1 mK. The atoms remained trapped in this chilly state for some 12.3 s, which is comparable to that achieved with alkali atoms. Based on their success, the researchers predict that MOTs could be easily customized for cooling other main group-III atoms.
Nicholson’s team have yet to use their setup to perform quantum measurements on ultracold indium atoms, but they believe that their technique will provide a robust platform for such experiments in future studies. By opening up a new area of the periodic table, they hope that their approach will inspire entirely new types of research in ultracold atomic physics. This could lead to the creation of exotic quantum phenomena that have never been seen before.
The research is described in Physical Review A.