Cold Radioactive Molecules Prepared for Next Physics Breakthroughs

For the first time, researchers have produced radium-containing molecules in a cold, laser-ready state, enabling high-precision tabletop measurements. The work opens a new experimental route for probing how the universe became dominated by matter rather than antimatter.

In the early universe, matter and antimatter were expected to form in nearly equal amounts. Yet when an electron meets its antimatter counterpart, the positron, both annihilate into energy—so the persistence of ordinary matter today hints at an unknown asymmetry generated during the cosmos’s earliest moments.

To explore that asymmetry, a team led by Nick Hutzler at Caltech turned to radium. Its nucleus has a rare “pear-shaped” deformation, which amplifies subtle signals that could arise from previously unseen particles or forces. When such nuclei are embedded within molecules, laser spectroscopy can reveal tiny energy shifts tied to fundamental physics.

Radium is notoriously difficult to work with: it is radioactive, chemically reactive, and available only in minute quantities. The central challenge was therefore not only forming radium-bearing molecules, but doing so in a controlled way that preserves the atoms long enough to study them precisely.

The researchers designed a strategy that begins by stabilizing radium in a viscous medium produced through a process inspired by candy-making. Instead of sugar, they optimized conditions using xylitol to avoid problematic caramelization while creating a workable “goo” that can be handled safely and reproducibly.

Once prepared, the material was placed onto a gold foil inside a compact cryogenic apparatus. The chamber was cooled to roughly minus 450°F using helium gas. Radium atoms were then excited by lasers into a reactive state so they could form the target molecular species.

Finally, additional laser systems were used to detect and characterize the newly created molecules at quantum-relevant energies. The result is a method that yields cold radioactive molecules suitable for precision experiments, and it can be extended to other heavy atoms with similarly favorable nuclear structure.

Hutzler’s group is already pursuing next-generation measurement concepts, including “engineered molecular clocks,” designed to reduce sensitivity to noise and decoherence. In future experiments, these tools will be applied to the radium nucleus as the collaboration searches for evidence of new symmetry-violating physics.

Keywords

Antimatter, Quantum mechanics, Atomic physics, Nuclear physics, Subatomic particles