Crystalline structures, or “density waves,” have been created in an atomic gas in a novel way by EPFL researchers. One of the most difficult problems in physics, figuring out how quantum stuff behaves, can be simplified with new information. Nature published the study results on May 24.
“Cold atomic gases were well known in the past for the ability to ‘program’ the interactions between atoms,” explains Professor Jean-Philippe Brantut from EPFL. The results of our experiment double that potential. They discovered a significant discovery while working with Professor Helmut Ritsch’s group at the University of Innsbruck, which may have far-reaching consequences for the future of quantum research and technologies.
Density waves
The process by which materials organize themselves into ordered structures like crystals has long piqued the curiosity of scientists. Like a group of people wearing different colored shirts standing in a line, but in a pattern where no two people with the same color shirt stand next to each other, particles in the often-mysterious realm of quantum physics can self-organize into “density waves,” where particles arrange themselves into a regular, repeating pattern or order.
Metals, insulators, and superconductors are all known to exhibit density waves. Superfluidity is a feature that permits particles to flow without resistance, but researching it has proven challenging because it often occurs alongside this order (the patterns of particles in the wave).
It’s important to remember that superfluidity isn’t just interesting in a theoretical sense; it’s also highly relevant for the creation of novel materials with interesting properties, such as high-temperature superconductivity, which could improve energy transfer and storage, and quantum computing.
Tuning a Fermi gas with light
Brantut and his coworkers developed a “unitary Fermi gas,” a narrow gas of lithium atoms cooled to extremely low temperatures and where atoms clash with each other very often, to investigate this dynamic.
Scientists put the gas within an optical cavity, a device that keeps light contained in a tiny volume for a long time. Photons, the particles of light, accumulate inside an optical cavity comprised of two opposing mirrors that reflect incoming light back and forth between them thousands of times.
The cavity was utilized to create long-range interactions between the Fermi gas particles, with one atom emitting a photon that was reflected by the mirrors and reabsorbed by another atom in the gas. The atoms self-organize into a density wave pattern when enough photons are emitted and reabsorbed, a parameter that can be easily adjusted in the experiment.
Brantut explains that the intense interactions of the Fermi gas, where atoms collide with each other and exchange photons across great distances, constitute a new sort of matter. As the authors put it, “We hope what we will see there will improve our understanding of some of the most complex materials encountered in physics.”