Researchers at the University of Vienna have demonstrated quantum interference in sodium nanoparticles containing more than 7,000 atoms—and produced clusters of nearly 10,000—showing that even large metallic particles can exhibit quantum behavior. Lead author Sebastian Pedalino said the results challenge the assumption that such objects must behave classically, confirming that quantum mechanics remains valid at this scale without the need for alternative models.
The team, led by Markus Arndt and Stefan Gerlich, achieved the breakthrough using sodium clusters exceeding 170,000 atomic mass units, larger than most proteins, marking a significant advance toward the long-sought goal of sustaining quantum superposition in increasingly complex systems.
The test was conducted using the multi-scale cluster interference experiment (MUSCLE).
To observe interference, the team had to minimize environmental disturbances that would destroy coherence. They produced the sodium clusters under cryogenic conditions (77 K, the temperature of liquid nitrogen) to reduce thermal decoherence, and ran the interferometer in ultra-high vacuum (about 9 × 10⁻⁹ mbar, roughly 10⁻¹¹ of atmospheric pressure) to limit collisions with gas molecules.
The scientists produced sodium clusters containing roughly 5,000 to 10,000 atoms and sent them through a three-grating interferometer made from standing ultraviolet laser light. The first grating spatially confined the particles to build up coherence, and the second grating acted as a beam splitter for the clusters’ matter wave. Scanning the third grating revealed an interference fringe pattern, and the team showed the fringe visibility followed the quantum prediction rather than a classical shadow-pattern model
The study achieved a macroscopicity value of 15.5. This metric quantifies how strictly an experiment tests the limits of quantum theory. This study has a value 10 times higher than any previous experiment.
This new level of sensitivity presents new opportunities for nanotechnology and materials science, opening new doors for measuring properties of nanoparticles and investigating the transition of matter from individual atoms to bulk metallic solids.
For more information: University of Vienna
Image: MUSCLE at the University of Vienna, where quantum interference of massive nanoparticles was detected. To isolate vibrations, the experiment is mounted on a table weighing several tons that floats on an air cushion. Credit: S. Pedalino / Uni Wien
