Physicists at the Vienna University of Technology (TU Wien) have detected quantum entanglement inside a crystal big enough to hold in your hand—an unremarkable-looking, centimeter-sized piece of a so-called “strange metal”—in work that may open a road to one of the great unsolved problems of physics: high-temperature superconductivity. The result was published in Nature Physics (“Quantum Fisher information in a strange metal” by Mazza, F., Biswas, S., Yan, X. et al.) and popularized under the memorable title “Schrödinger’s anthill.”
Quantum entanglement, in which particles behave as a single system, no matter how they are separated, is usually coaxed into existence in isolated laboratory set-ups of a few particles at a time, such as in quantum computing. What the TU Wien team showed is that entanglement can also pervade a macroscopic solid. Firing neutrons at a crystal of cerium, palladium, and silicon and analyzing how they scattered—using a mathematical measure called quantum Fisher information—they found a response impossible to explain in terms of independent particles. Instead, groups of at least nine entities are entangled and act collectively.
The significance runs deeper than the curiosity of a hand-sized Schrödinger’s cat. “Strange metals,” whose temperature-resistance relationship is unlike that of typical metals, belong to the same family as the high-temperature superconductors: materials that carry electricity with zero resistance, whose inner workings remain a mystery in the decades since their discovery. If this collective entanglement is the hidden order behind strange-metal behavior, it may be key to that mystery as well.
