One dimensional quantum lattice liquids
A team of researchers has recently discovered a new type of quantum droplets in ultracold atomic systems.
Liquids are ubiquitous in Nature. From the water that we consume daily to superfluid helium, which is a quantum liquid appearing at temperatures as low as only a few degrees above the absolute zero. A common feature of these vastly different liquids is being self-bound in free space in the form of droplets. Understanding from a microscopic perspective how a liquid is formed, by adding particles one by one, is a significant challenge.
Recently, a new type of quantum droplets has been experimentally observed in ultracold atomic systems. The article, published in Physical Review Letters, presents a microscopic theory of lattice quantum droplets, which explains their formation. The team is formed by researchers Ivan Morera and Prof. Artur Polls from the Institute of Cosmos Sciences of the University of Barcelona, in collaboration with Prof. Grigori Astrakharchik from the UPC, and led by Prof. Bruno Juliá-Díaz, also from ICCUB and researcher for the QUASI-CAT project on cold atom quantum simulators in Catalonia.
How do quantum droplets form?
This new type of quantum droplets is made of alkaline atoms, which are cooled down to extremely low temperatures of the order of nanokelvins. The main peculiarity of these systems is that they are the most dilute liquids ever experimentally observed. An extraordinary experimental control over the system opens the possibility of unraveling the mechanism leading to the formation of quantum droplets.
Furthermore, the article shows that this formation of the quantum droplet can be explained in terms of effective interactions between dimers, also known as the bound states of two particles. By solving the four-body problem, they have shown that tetramers -bound states of four particles- can appear and be interpreted as simple bound states of two dimers.
The properties of these tetramers already coincide with the ones of large quantum droplets, which indicates that many of the feature properties of the many-body liquid are contained in the tetramer. They also discussed the possibility of observing these strongly correlated droplets in dipolar bosons or bosonic mixtures in optical lattices.
Reference: Ivan Morera, Grigori E. Astrakharchik, Artur Polls, and Bruno Juliá-Díaz. Universal Dimerized Quantum Droplets in a One-Dimensional Lattice. Phys. Rev. Lett. 126, 023001 (2021).