The "Universe" in a Glass: Low Temperature, Quantum, and Superfluidity

Keiya Shirahama (Associate Professor, Department of Physics)

The world we live in contains various "hierarchies," such as elementary particles, atoms, molecules, matter, and the universe, but the phenomena that occur within them all follow common physical laws. One of the goals of physics is to clarify this "universality" of nature. On the other hand, there are phenomena that can never be predicted from the behavior of a single constituent element, such as the "superconductivity" exhibited by a large number of electrons in a metal at extremely low temperatures. When a hierarchy formed by a collection of many elements exhibits completely new properties, it is called "emergence," which, along with universality, has become a fundamental concept in modern physics. Even the various "things" we casually handle every day, such as water and the glass that holds it, conceal properties linked to these two concepts.

How can we investigate the properties hidden within matter? The most effective method is to lower the temperature. At low temperatures, the true nature of a substance, which is hidden by "heat" at high temperatures, emerges. Much of this nature is a manifestation of "quantum mechanical properties," where the constituent atoms and electrons of the substance can also behave as "waves." The most dramatic manifestation of this quantum behavior is a phenomenon called "superfluidity," which liquid helium exhibits at the extremely low temperature of minus 270 degrees Celsius. Helium in a superfluid state loses its viscosity and exhibits strange properties, such as climbing the walls of its container. The essence of this phenomenon is believed to lie in the fact that helium atoms possess the properties of both "particles" and "waves."

We are experimentally investigating the "universality" and "emergence" of helium from various aspects and are discovering one new, previously unknown property after another. The liquid helium in a glass is a small "universe" where many unknown properties still lie hidden.