An international team of physicists have used atoms about 3 billion times colder than interstellar space to open a portal to an unexplored realm of quantum magnetism. The results were published Sept. 1 in Nature Physics. “Fermions are not rare particles. They include things like electrons and are one of two types of particles that all matter is made of.”

A Kyoto team led by Yoshiro Takahashi used lasers to cool up to 300,000 ytterbium atoms, within about one-billionth of a degree of absolute zero, the unattainable temperature where all motion stops. That’s about 3 billion times colder than interstellar space, which is still warmed by the afterglow from the Big Bang.

At such low temperatures, quantum behavior emerges even in large collections of particles. Cooling matter to these unprecedented low temperatures allows experimental observations, initially benchmarked against calculations, to be extended to regimes that can't be modeled on a computer, said Richard Scalettar, distinguished professor in the Department of Physics and Astronomy at UC Davis and a coauthor on the paper.

Electrons in solids can come in different ‘flavors,’ Scalettar said. They have two possible directions for their "spin" (the way they rotate about their axes) and they also can occupy different atomic orbitals (energy bands). But in almost all situations in solid state physics, these flavors each have different energy, that is, the flavors are not equivalent. “What is unique about this new work is that the (cold atom) experimentalists have found a way to build a system of quantum particles which are completely symmetric. This leads to beautiful and novel states of quantum matter when the atoms are cooled," Scalettar said. Study coauthor Eduardo Ibarra-García-Padilla, said this captures the minimal ingredients to understand why solid materials become metals, insulators, magnets or superconductors.

An artist’s conception of the complex magnetic correlations observed with a quantum simulator at Kyoto University. Galaxy simulations from FIRE-2

An open source software package was one of the primary theory tools used in the study. The software resulted from work by Scalettar and Professor Zhaojun Bai, UC Davis Department of Computer Science. Ibarra-García-Padilla will join UC Davis this Fall as a postdoctoral researcher.