A density wave (DW) is a fundamental type of long-range ordering in quantum matter, coupled with self-organization in a crystalline structure. Although density waves are seen in a wide variety of materials, such as metals, insulators, and superconductors, studying them has proven challenging, especially when this order (the patterns of the wave particles) interacts with other types of organization, such as superfluidity, resulting in particles with no resistance. can flow.

EPFL scientists have found a new way to create a “density wave” in an atomic gas. The findings could lead to a better understanding of the behavior of quantum matter.

EPFL Professor Jean-Philippe Brantut said: “Cold atomic gases were known in the past for their ability to ‘program’ the interactions between atoms. Our experiment doubles this power!”

To study this interaction, Brantut and his colleagues created a “unitary Fermi gas,” a thin gas of lithium atoms cooled to incredibly low temperatures where atoms often collide.

The scientists then placed this gas in an optical cavity, a device for constraining light in a small area for a long time. Two opposing mirrors that reflect back and forth incoming light countless times form optical cavities, allowing light particles or photons to accumulate in the cavity.

In the study, the researchers used the cavity to allow the particles of the Fermi gas to interact over great distances: no matter how far it is from the first atom, the second atom of the gas will always absorb the photon it first atom of the first atom emits and reflects. away from the mirrors. The atoms form a density wave pattern when a sufficient amount of photons are collectively released and reabsorbed – easily controlled in the experiment.

Brantut said, “The combination of atoms directly colliding with each other in the Fermi gas, while simultaneously exchanging photons over a long distance, is a new kind of matter where the interactions are extreme. We hope that what we see there will improve our understanding of some of the most complex materials encountered in physics.”

Magazine reference:

  1. Victor Helson, Timo Zwettler, Farokh Mivehvar, Elvia Colella, Kevin Roux, Hideki Konishi, Helmut Ritsch, Jean-Philippe Brantut. Density wave ordering in a unitary Fermi gas with photon-mediated interactions. Nature May 24, 2023. DOI: 10.1038/s41586-023-06018-3