A new way to create density waves of quantum matter Nature Express

Density waves (DW) are a fundamental type of long-range order (LRO) in quantum matter, associated with self-organized (self-organizing) crystal structures. Although density waves have been studied in a wide range of materials (e.g., metals, insulators, and superconductors), studying them remains extremely challenging; especially when this order (patterns of particles in waves) coexists with other types (e.g., superfluidity) of organization, which allows for resistance-free particle flow.

Illustration of a density wave

Now, scientists at the University of Innsbruck and the Ecole Polytechnique Fédérale de Lausanne (EPFL) have discovered a new way to create "density waves" in atomic gases. This discovery may lead to a better understanding of the behavior of quantum matter.

The research was published in the journal Nature on May 24 under the title "Density-wave ordering in a unitary Fermi gas with photon-mediated interactions".

The concept of the experiment

Commenting on the breakthrough, Professor Jean-Philippe Brantut of EPFL said, "Cold atomic gases have been known in the past for their ability to 'program' interatomic interactions. Now, with this experiment, we have doubled that ability!"

To study such interactions, Brantut and his colleagues created a "unitary Fermi gas": a thin gas of lithium atoms that has been cooled to incredibly low temperatures and in which the atoms often clash.

Scientists next placed this gas in a light cavity, a tool that confines light to a small area for a long time. Two mirrors facing each other reflecting incident light back and forth between them countless times make up the optical cavity, which allows light particles or photons to accumulate inside the cavity.

In this study, the researchers used the cavity to make the particles of the Fermi gas interact at great distances: no matter how far it is from the first atom, the second atom of the gas always absorbs the first emitted photon of the first atom and bounces off it to the mirror. When a sufficient number of photons are collectively released and reabsorbed, the atoms form a density wave pattern: this is easily controlled in the experiment.

Phase diagram of the system

"Our platform complements ongoing research in the field of cavity-coupled strongly correlated materials," the experimental team said.

The combination of atoms colliding directly with each other in a Fermi gas while exchanging photons over long distances is a new type of matter whose interactions are extreme," Brantut said. We hope what we see there will improve our understanding of some of the most complex materials we encounter in physics."

Reference links:

[1] https://www.nature.com/articles/s41586-023-06018-3

[2]https://www.eurasiareview.com/25052023-quantum-matter-breakthrough-tuning-density-waves/

[3] https://www.techexplorist.com/new-way-create-crystalline-structure-called-density-wave/60586/