Researchers at Rice University and TU Wien have achieved a major breakthrough in the study of quantum materials, experimentally measuring quantum entanglement in a quantum critical metal, a class of materials more commonly known as “strange metals.” Published in Nature Physics, the work is the strongest evidence yet that entanglement is a fundamental ingredient in the behavior of these exotic materials, and may open the door to advances in superconductivity and quantum computing.
Strange metals have puzzled physicists for decades, as they don’t follow the normal rules of electrical conduction. For ordinary metals like copper and gold, Fermi liquid theory works well. Strange metals work in a completely different way.
What are exactly Strange Metals? But, unlike normal metals like copper or gold, the electrical resistance of strange metals is directly proportional to temperature. They break the rules of the standard Fermi liquid theory, which considers electrons to be mostly independent particles. Instead, they are in a special state of matter where the electrons lose their individuality and act collectively, as a highly coordinated quantum system.
The new study concerns quantum entanglement, one of the most fascinating and counterintuitive ideas in modern physics.
What is Quantum Entanglement? It is a phenomenon where two or more particles become so entangled that the state of one instantaneously influences the other(s), no matter how far apart they are. This was called “spooky action at a distance” by Albert Einstein, who could not quite reconcile this with the classical ideas of space and time. In strange metals, though, entanglement goes far beyond pairs of particles, with billions of electrons acting collectively as a single quantum object.
The research team, headed by theoretical physicist Qimiao Si, wanted to test a long-standing prediction that entanglement is a defining feature of strange metals. Such a phenomenon has long been considered nearly impossible to measure in a complex many-electron system.
How did scientists measure such “spooky” things? They employed a sophisticated statistical device from quantum information theory known as Quantum Fisher Information, or QFI. They mathematically determined the degree of quantum entanglement present in a crystal by analyzing how the crystal responded to neutron scattering experiments. Their measurements showed that entanglement reaches a dramatic maximum at the quantum critical point—the exact point at which the material transitions from one quantum state to another. But the discovery does more than confirm theoretical predictions. It also deepens an unlikely link between condensed-matter physics and some of the most extreme objects in the universe.
Why do physicists talk about black holes? Strange metals and black holes seem to share a strange property – they dissipate energy at the maximum possible rate allowed by the laws of physics, a limit known as Planckian dissipation. Theoretical frameworks such as the Sachdev-Ye-Kitaev (SYK) model suggest that the intricate entanglement structure observed in strange metals could be mathematically similar to the physics at a blackhole’s event horizon, hinting at an interesting connection between quantum materials and gravity. The work has not only scientific significance, but could have profound technological ramifications.
What does this mean for us going forward? High-temperature superconductivity is often found together with strange metals. Deciphering the essence of this “entangled quantum soup” could aid scientists in creating materials capable of conducting electricity with no resistance at far higher temperatures — possibly even at room temperature. The breakthrough would revolutionize energy transmission, computing infrastructure, transportation systems and next-generation quantum technology development.
Their work opens a new experimental window on one of the most enduring mysteries of condensed matter physics, by making the first direct measurement of entanglement in a strange metal. Their findings not only confirm decades of theoretical work, but also bring scientists a step closer to tapping the extraordinary potential hidden inside quantum matter.
