The atoms arranged in lines and sheets reached about 1.2 nanokelvin, more than 2 billion times colder than interstellar space. For the atoms in three-dimensional arrangements, the situation is so complex that the researchers are still figuring out the best way to measure the temperature.

The atoms in the experiment belong to a larger group called fermions and were “the coldest fermions in the universe”, says Hazzard. “Thinking about experimenting on this 10 years ago, it looked like a theorist’s dream,” he says.

Physicists have long been interested in how atoms interact in exotic magnets like this because they suspect that similar interactions happen in high-temperature superconductors – materials that perfectly conduct electricity. By better understanding what happens, they could build better superconductors.

Be it magnets or superconductors, materials are known for their various properties. However, these properties may change spontaneously under extreme conditions. Researchers at the Technische Universität Dresden (TUD) and the Technische Universität München (TUM) have discovered an entirely new type of these phase transitions. They display the phenomenon of quantum entanglement involving many atoms, which previously has only been observed in the realm of a few atoms. The results were recently published in the scientific journal Nature.

New fur for the quantum cat

In physics, Schroedinger’s cat is an allegory for two of the most awe-inspiring effects of quantum mechanics: entanglement and superposition. Researchers from Dresden and Munich have now observed these behaviors on a much larger scale than that of the smallest of particles. Until now, materials that display properties, like magnetism, have been known to have so-called domains—islands in which the materials properties are homogeneously either of one or a different kind (imagine them being either black or white, for example).

Protons are particles that exist in the nucleus of all atoms, with their number defining the elements themselves. Protons, however, are not fundamental particles. Rather, they are composite particles made up of smaller subatomic particles, namely two “up quarks” and one “down quark” bound together by force-carrying particles (bosons) called “gluons.”

This structure isn’t certain, however, and quantum physics suggests that along with these three quarks, other particles should be “popping” into and out of existence at all times, affecting the mass of the proton. This includes other quarks and even quark-antiquark pairs.

Indeed, the deeper scientists have probed the structure of the proton with high-energy particle collisions, the more complicated the situation has become. As a result, for around four decades, physicists have speculated that protons may host a heavier form of quark than up and down quarks called “intrinsic charm quarks,” but confirmation of this has been elusive.

A cold-atom experiment suggests that interactions between particles can induce the coexistence of localized and extended states in a quantum wire.