\n<\/p>\n
Schr\u00f6dinger\u2019s cat just got a little bit fatter. Physicists have created the largest ever \u2018superposition\u2019 \u2014 a quantum state in which an object exists in a haze of possible locations at once.<\/p>\n
A team based at the University of Vienna put individual clusters of around 7,000 atoms of sodium metal some 8 nanometres wide into a superposition of different locations, each spaced 133 nanometres apart. Rather than shoot through the experimental set up like a billiard ball, each chunky cluster behaved like a wave, spreading out into a superposition of spatially distinct paths and then interfering to form a pattern researchers could detect.<\/p>\n
\u201cIt\u2019s a fantastic result,\u201d says Sandra Eibenberger-Arias, a physicist at the Fritz Haber Institute in Berlin.<\/p>\n
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Quantum theory doesn\u2019t put a limit on how big a superposition can be, but everyday objects clearly do not behave in a quantum way, she explains. This experiment \u2014 which puts an object as massive as a protein or small virus particle into a superposition \u2014 is helping to answer the \u201cbig, almost philosophical question of \u2018is there a transition between the quantum and classical?\u2019,\u201d she says. The authors \u201cshow that, at least for clusters of this size, quantum mechanics is still valid\u201d.<\/p>\n
The experiment, described in Nature on 21 January, is of practical importance, too, says Giulia Rubino, a quantum physicist at the University of Bristol, UK. Quantum computers will ultimately need to maintain perhaps millions of objects in a large quantum state to perform useful calculations. If nature were to make systems collapse past a certain point, and that scale was smaller than what is needed to make a quantum computer, \u201cthen that\u2019s problematic,\u201d she says.<\/p>\n
Physicists have long debated how the classical, everyday world emerges from an underlying quantum one. Quantum theory \u201cnever states it stops working above a certain mass or size,\u201d says Sebastian Pedalino, a physicist at the University of Vienna and a co-author of the study.<\/p>\n
In 1935, the Austrian physicist Erwin Schr\u00f6dinger showed the absurdity of common interpretations of quantum mechanics with his famous cat-based thought experiment. The cat is put into a box with vial of poison, which will be released if a radioactive atom decays. If the box remains isolated from its environment, the atom exists in a superposition of both decayed and not-decayed, and until observed, the cat is an undefined state of both dead and alive.<\/p>\n
In the real world, objects eventually become too complex or interact too much to maintain a superposition, an idea known as decoherence. But there are also extensions to quantum mechanics, known as collapse theories, that suggest that beyond a certain point, a system will inevitably reduce to a classical state, even in isolation. These theories were picked by 4% of researchers as their favourite interpretation of quantum mechanics in a 2025 Nature survey. \u201cThe only way to answer this question is by scaling up\u201d quantum experiments, says Rubino.<\/p>\n
To do this, Pedalino and his team generated a beam of clusters at 77 degrees kelvin (\u2212196 \u00baC) in an ultra-high vacuum. The researchers put the beam through an interferometer consisting of three gratings constructed with laser beams. The first channelled the clusters through narrow gaps, from which they spread out and travelled in sync as waves; they then passed through a second set of slits that made the waves interfere in a distinctive pattern, which could be detected using the final grating.<\/p>\n
Viewing such quantum effects at scale is difficult, because stray gas molecules, light or electric fields can disrupt the delicate quantum state, and the slightest misalignment of the gratings or minute force can blur the fine interference pattern. It took two years for the team to be able to see the signal, says Pedalino. Before that, he spent \u201cthousands of hours\u201d in a basement laboratory looking at \u201cflat lines and noise\u201d, he says.<\/p>\n
The team\u2019s superposition is ten times bigger than the previous record. That\u2019s according to a measure known as \u2018macroscopicity\u2019, which combines mass with how long the quantum state lasts and how separated the states are. However, this doesn\u2019t mean it\u2019s the largest mass ever put into a superposition, says Rubino. In 2023, another team put a 16-microgram vibrating crystal into a superposition \u2014 but that was only over a distance of two billionths of a nanometre.<\/p>\n
Scaling up further will not be easy, says co-author Stefan Gerlich, also at the University of Vienna. More-massive particles have shorter wavelengths, which make it harder to distinguish quantum predictions from classical ones. However, Gerlich says that 15 years ago, he thought today\u2019s experiment was \u201cnot possible\u201d.<\/p>\n
The team is also working on putting biological matter through the same experimental set-up. Some viruses are a similar size to the clusters, but they tend to be more fragile and can fragment during flight, which makes the experiment harder to do \u2014 although not impossible. \u201cI think that it\u2019s not so far out of reach anymore,\u201d says Pedalino.<\/p>\n
Although a virus is not considered to be alive, experiments with biological matter \u201cwould move the entire quantum interference into a new regime,\u201d he adds.<\/p>\n
This article is reproduced with permission and was first published on January 21, 2026.<\/p>\n","protected":false},"excerpt":{"rendered":"
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