Two ultracold lithium atoms remain bound in a molecule even though they possess enough energy to fly apart. Researchers from the University of Kaiserslautern-Landau in Germany demonstrated this for the first time in an experiment published on 9 November 2026 in Nature Physics.
The team, led by Professor Artur Widera and with first author Alexander Gutman, cooled lithium atoms to a temperature below one microkelvin. Using rapidly oscillating magnetic fields, they brought two molecular resonances closer together and created the conditions for quantum interference. Under ordinary conditions, energy above the threshold would lead to dissociation, but here the decay was suppressed.
Atoms behave not only as particles but also as waves. When decay waves through different channels overlap with the right phase, they cancel each other out — just as in active noise-cancelling headphones, where a generated wave destroys external noise. As a result, the molecule remains intact, even though formally its energy allows it to decay.
The scientists checked the state by atom loss from the cloud, gas dynamics and radio-frequency spectroscopy. Without the protective interference, significantly more atoms flew away. The method builds on their previous work from 2025 in Science Advances, where they learned to precisely control interactions in an ultracold gas.
This is the first experimental confirmation of the bound states in the continuum mechanism in collisions of ultracold atoms. Such states had been predicted theoretically since 1985 and observed in optics and acoustics, but in atomic systems a controlled effect was achieved only now.
The discovery provides a new tool for protecting quantum states from the environment. In the future, this could help create more stable qubits and sensors, where unwanted decay is suppressed by the very nature of quantum interference.
The results show how the wave nature of matter turns an expected loss into a protective mechanism, opening the way to new ways of controlling quantum systems.
