Experimental atomic physicists have discovered there is a maximum amount of electrical resistance, or resistivity, that can result from collisions between electrons.

A team from the University of Toronto, L’École Normale Supérieure in Paris, and Lehigh University in Pennsylvania studied ultracold potassium atoms cooled to near absolute zero. They found that when increasing the rate at which atoms collide, the resulting resistance eventually stops increasing, offering new insights into what causes resistivity at the microscopic level.

“Electron-on-electron collisions are known to increase resistivity in some pure materials,” explains Professor Joseph Thywissen in the Department of Physics and the Centre for Quantum Information and Quantum Control in the Faculty of Arts & Science at the University of Toronto, senior author of a study published in Physical Review Letters. “The energy produced by electrical resistance shows up as heat. Transmission lines, for instance, lose up to 8% of generated electrical power. Resistivity is also interesting to study because it can be a signature of new physics in materials.”

Many quantum effects can be observed only when a small number of particles is studied—individual atoms, molecules or photons, for example, carefully shielded from the rest of the world. But what about macroscopic objects, consisting of an unimaginably large number of particles? Can they, too, display effects that provide a direct glimpse into the quantum world?

Experimentalists at TU Wien have now shown that this is possible: A centimeter-sized crystal of a so-called strange metal was investigated, and a high degree of quantum entanglement was detected. This was made possible by a clearly defined method from quantum information theory: the quantum Fisher information.

It establishes a new bridge between solid-state physics and quantum physics: Quantum entanglement can be directly quantified in a macroscopic strange-metal material. The paper is published in the journal Nature Physics.