University of Vienna Shows Metal Clumps of 10,000 Atoms Can Exist in Two Places at Once, Rewriting Quantum Limits

Scientists at the University of Vienna have demonstrated quantum mechanical behavior in metallic nanoparticles ten times larger than any previously tested, pushing the known boundary of where the counterintuitive laws of quantum physics apply and opening a new front in one of the oldest debates in modern science: why the quantum world seems to vanish at the scale of everyday objects. The experiments, published in the journal Nature and involving metallic sodium clusters containing between 5,000 and 10,000 atoms, showed that even relatively massive chunks of metal can exist in a quantum superposition — occupying two positions simultaneously — in defiance of common sense.

The experimental team, led by doctoral student Sebastian Pedalino at the University of Vienna in collaboration with researchers from the University of Duisburg-Essen, generated cold clusters of sodium atoms and fired them through three diffraction gratings created by ultraviolet laser beams — a quantum version of the famous double-slit experiment that Richard Feynman once called the central mystery of quantum mechanics. The clusters, with a diameter of roughly 8 nanometers and a mass exceeding 170,000 atomic mass units, produced clear interference patterns that can only arise if each particle traveled through both gratings simultaneously, confirming quantum superposition at a scale comparable to modern transistor structures and larger than most protein molecules.

"Intuitively, one would expect such a large lump of metal to behave like a classical particle," said Pedalino. "The fact that it still interferes shows that quantum mechanics is valid even on this scale and does not require alternative models." The experiment achieved a macroscopicity value — a technical measure of how large and massive a superposition is — of μ = 15.5, surpassing all previous matter-wave interference experiments with objects of comparable mass and composition.

The significance of the result extends well beyond its immediate experimental parameters. One of the most enduring puzzles in physics is why quantum effects — superposition, entanglement, wave-particle duality — are so conspicuous in electrons and photons but appear absent in the objects of everyday experience. Leading theories suggest that quantum effects do in principle apply to all objects, but that the sheer number of interactions between large objects and their environments causes quantum superpositions to collapse almost instantaneously, a process called decoherence. The Vienna experiment pushes the observed onset of that collapse to larger scales than previously demonstrated, giving theorists new data to test competing models of why the quantum-classical boundary sits where it does.

The team is already planning experiments with objects hundreds of times larger than the current sodium clusters. The practical applications of such research include the development of ultra-sensitive quantum sensors, which could detect gravitational waves, map brain activity, or navigate without GPS by measuring the quantum interference of matter waves with extraordinary precision. More fundamentally, the Vienna results add to a growing body of experimental evidence suggesting that the universe may be profoundly, inescapably quantum at scales far larger than physicists once believed — and that the classical world we experience is not a departure from quantum mechanics but a special limiting case of it.