Quantum phenomena are usually associated with very small objects, such as individual atoms, molecules, or photons, that must be carefully isolated from their surroundings. But do the same strange quantum effects exist in objects large enough to see and touch?
Researchers at the Vienna University of Technology have provided convincing evidence that it is possible. By studying centimeter-sized crystals made of a type of material known as strange metals, researchers have detected a high degree of quantum entanglement, one of the most remarkable features of quantum physics. They accomplished this using a quantum information science technique called quantum Fisher information.
This result shows that quantum entanglement can be directly measured in macroscopic unknown metals, creating a new link between quantum information and solid-state physics.
From Schrödinger’s cat to anthill
Whether quantum mechanics applies only to small particles or to larger objects has been debated since the field’s early days. Physicist Erwin Schrödinger famously explained this mystery with a thought experiment using a cat that was both alive and dead until he observed it. Since then, scientists have repeatedly pushed the limits of how large systems can exhibit quantum behavior.
A team from the Vienna University of Technology approached the problem from a different angle.
“Our approach is different,” says Professor Silke Bühler-Paschen of the Institute for Solid State Physics at the Vienna University of Technology. “We are not trying to make the entire crystal a superposition of two states. Instead, we are asking whether its components – collectively – are in such an entangled state.”
Bühler-Paschen says the experiment is more like an anthill than a Schrödinger’s cat. When an anthill is disturbed, a response occurs from the colony acting together rather than from the individual ants. The researchers wanted to determine whether the particles within the crystal behaved in a similarly tuned way.
Quantum Fisher’s information reveals hidden tangles
The theoretical framework behind this experiment was developed by Innsbruck quantum physicist Peter Zurer and his colleagues. Their work showed that quantum Fisher information can be used to identify quantum entanglement, even in complex systems consisting of vast numbers of interacting particles.
“Quantum Fischer information quantifies how sensitive a quantum system is to changes,” explains Bühler-Paschen. “For a collection of independent particles, the response is limited because each particle contributes uniquely. But when the particles are entangled, the whole system can respond more strongly than the sum of its parts. It is this increased sensitivity that makes entanglement so valuable for quantum metrology. Quantum metrology aims to detect extremely small signals with the highest possible precision. Therefore, by measuring how strongly a system responds to a perturbation, we can infer the degree of entanglement present in a material.”
Simply put, strongly entangled systems respond more dramatically to disturbances than collections of independent particles, allowing researchers to estimate how much entanglement is present.
Strange metal crystals exhibit collective quantum behavior
To test this idea, the researchers created crystals made of cerium, palladium, and silicon. This material belongs to a class of strange metals that have long fascinated physicists because it exhibits unusual quantum properties that are only partially understood.
At Grenoble’s Laue-Langevin Institute (ILL), PhD student Federico Mazza bombarded crystals with neutrons and measured their reactions.
“In normal matter, you would expect neutrons to transfer their energy to individual particles,” Mazza said. “However, when we analyzed the data using quantum Fisher information, we found a response that cannot be explained in terms of independent particles. Instead, we show that a group of at least nine quantum entangled entities are acting collectively.”
The measurements provide direct evidence of strong multicomponent quantum entanglement in solid crystals small enough to fit in the palm of your hand.
Solve the mystery of strange metals
The researchers initially aimed to better understand why the strange metal behaved so differently from conventional materials. Similar behavior is seen in other systems such as high-temperature superconductors.
Interest in strange metals has surged in recent years as scientists discover more and more unexpected properties. In 2025, researchers at the Vienna University of Technology and Rice University reported that electrical current passes through these materials with unusually low electrical noise. Newly observed quantum entanglement may help explain why. Rather than operating independently, the particles appear to coordinate their behavior in a way that suppresses fluctuations in the current.
“What we are looking at here is general physical principles rather than details of specific materials,” says the study’s lead theorist, Fahel Assaad of the University of Wurzburg. “The strong entanglement appears to be directly related to the unusual behavior of strange metals.”
Towards future quantum technology
The researchers believe this work shows the value of integrating ideas from quantum information science and condensed matter physics.
“The results were a huge success for us,” says Silke Bühler-Paschen. “They confirm that our unusual approach of using quantum information science techniques to study the solid-state physics of novel materials can reveal fundamentally new insights.”
The team is now looking at a reverse exchange. They hope to determine whether the strange metal could ultimately be useful in quantum technologies, such as sensitive quantum measurement systems that can detect very small signals with extraordinary precision.
