Up and Atom

U of G physicists examine ultracold particles in new ways, setting the stage for future breakthroughs.

At one time, people believed that atoms were the smallest things in the universe, impossible to split apart. Thanks to researchers like Ernest Rutherford who discovered the nucleus of the atom, we learned that atoms could be divided into smaller subatomic particles called protons, neutrons, and electrons; these are all fermions. Fermions make up solid objects and it is impossible for two fermions to be in the same place at the same time. Experiments on fermions have led to important breakthroughs—providing insight into atomic clocks, telecommunications, and even the inner workings of high-density collapsed stars.

Now, researchers from the University of Guelph (U of G) are proving that there is even more we can learn from fermions, particularly when we turn down the temperature. U of G physics professor Alexandros Gezerlis and his research team study ultracold atomic systems. The way fermions behave and interact within these frigid systems provides insight into the smallest known energy scale. This information can be used to create a model for the fundamental properties of the universe, including the behaviour of astronomical objects, such as neutron stars.

Fermions within ultra-cold systems experience forces and they even spin, a form of angular momentum. Up until now, researchers have focused on what is called the “two-component” fermion-system structure. This structure considers two types of fermions, which differ based on the direction of their spin: spin-up and spin-down. As an analogy, this kind of system is akin to one that is made up of neutrons only. Of course, in any nuclear system there are two additional components to consider—the spin-up and spin-down of protons. For the first time ever, the U of G team has scaled-up the fermion system structure problem by examining a system that involves the strong interactions between four fermion components. The research team has implemented novel microscopic simulation methods, involving an original four-species wave function (a kind of mathematical description) that sheds light on how fermions interact in this more complex system.

“We have made a step toward understanding fermionic clustering from first principles,” explains Gezerlis. “These findings can be tested experimentally in the future by manipulating the four-component fermion system in a laboratory setting.”

This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC); the Canada Foundation for Innovation (CFI); the Early Researcher Award (ERA) program of the Ontario Ministry of Research, Innovation, and Science; the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contracts No. DE-AC5206NA25396 and No. DE-FG0204ER41338; and by the European Union Research and Innovation program Horizon 2020 under Grant No. 654002. Computational resources were provided by SHARCNET and NSERC.

Dawkins WG, Carlson J, van Kolck U, Gezerlis A. Clustering of four-component unitary fermions. Phys Rev Lett. 2020 Apr 9. doi: 10.1103/PhysRevLett.124.143402.