Quantum physicists have just supersized Schrödinger’s cat. What happens next could be revolutionary

Schrödinger’s cat just got a little bigger. Physicists have created the largest “superposition” ever: a quantum state in which an object exists simultaneously in a haze of possible locations.

A team based at the University of Vienna placed individual clusters of about 7,000 sodium metal atoms about 8 nanometers wide in a superposition of different locations, each spaced 133 nanometers apart. Rather than passing through the experimental setup like a billiard ball, each large cluster behaved like a wave, propagating in a superposition of spatially distinct paths, then interfering to form a pattern that the researchers could detect.

“This is a fantastic result,” says Sandra Eibenberger-Arias, a physicist at the Fritz Haber Institute in Berlin.

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Quantum theory doesn’t set a limit on the magnitude of a superposition, but everyday objects clearly don’t behave quantumly, she explains. This experiment – ​​which superimposes an object as massive as a protein or a small viral particle – helps answer the “big, almost philosophical question of “is there a transition between the quantum and the classical?” “, she said. The authors “show that, at least for clusters of this size, quantum mechanics still holds.”

The experiment, described in Nature on January 21, also has practical importance, says Giulia Rubino, a quantum physicist at the University of Bristol, UK. Quantum computers may eventually need to maintain millions of objects in a large quantum state to perform useful calculations. If nature caused systems to collapse beyond a certain point, and that scale was smaller than what’s needed to make a quantum computer, “then that would be problematic,” she says.

Overlay size limit

Physicists have long debated how the classical, everyday world emerges from an underlying quantum world. Quantum theory “never states that it stops working above a certain mass or size,” says Sebastian Pedalino, a physicist at the University of Vienna and co-author of the study.

In 1935, Austrian physicist Erwin Schrödinger demonstrated the absurdity of common interpretations of quantum mechanics with his famous cat-based thought experiment. The cat is placed in a box containing a vial of poison, which will be released if a radioactive atom decays. If the box remains isolated from its surroundings, the atom exists in a superposition both decayed and undecomposed, and until observed, the cat is in an indefinite state of dead and alive.

In the real world, objects eventually become too complex or interact too much to sustain a superposition, an idea known as decoherence. But there are also extensions of quantum mechanics, known as collapse theories, which suggest that beyond a certain point a system will inevitably collapse to a classical state, even in isolation. These theories were chosen by 4% of researchers as their preferred interpretation of quantum mechanics. in 2025 Nature investigation. “The only way to answer this question is to develop” quantum experiments, explains Rubino.

To do this, Pedalino and his team generated a beam of clusters at 77 degrees Kelvin (−196 ºC) in an ultra vacuum. The researchers passed the beam through an interferometer made up of three arrays constructed with laser beams. The first channeled the clusters through narrow gaps, from which they spread and moved synchronously in the form of waves; they then passed through a second series of slits that caused the waves to interfere in a distinctive pattern, which could be detected using the final array.

A careful process

It is difficult to observe such large-scale quantum effects because stray gas molecules, light, or electric fields can disrupt the delicate quantum state, and the slightest misalignment of the lattices or a tiny force can scramble the fine interference pattern. It took the team two years to see the signal, Pedalino says. Before that, he spent “thousands of hours” in a basement lab studying “flat lines and noise,” he says.

The team’s overlap is ten times the previous record. This is revealed by a measurement known as “macroscopic”, which combines mass with the duration of the quantum state and the degree of separation of the states. However, that doesn’t mean it’s the largest mass ever put into superposition, Rubino says. In 2023, another team superimposed a vibrating crystal of 16 micrograms, but this only happened over a distance of two billionths of a nanometer.

It won’t be easy to go further, says co-author Stefan Gerlich, also at the University of Vienna. More massive particles have shorter wavelengths, making it more difficult to distinguish between quantum and classical predictions. However, Gerlich says that 15 years ago he thought the current experiment was “not possible.”

The team is also working on subjecting biological matter to the same experimental setup. Some viruses are similar in size to clusters, but they tend to be more fragile and can fragment during flight, making the experiment more difficult to perform, but not impossible. “I think it’s not so out of reach anymore,” Pedalino says.

Although a virus is not considered alive, experiments on biological matter “would move the whole quantum interference set into a new regime,” he adds.

This article is reproduced with permission and has been published for the first time January 21, 2026.