Quantum gases are very well suited for investigating the microscopic consequences of interactions in matter. Today, scientists can precisely control individual particles in extremely cooled gas clouds in the laboratory, revealing phenomena that cannot be observed in the every-day world. An exciting example is provided by recent experiments on magnetic atoms that have successfully created a supersolid state. The magnetic interaction causes the atoms to self-organize into droplets and arrange themselves in a regular pattern. Normally, one would think that each atom would be found in a specific droplet, with no way to get between them. However, in the supersolid state, each particle is delocalized across all the droplets, existing simultaneously in each droplet. So basically, on has a system with a series of high-density regions (the droplets) that all share the same delocalized atoms. This bizarre formation enables effects such as frictionless flow despite the presence of spatial order (superfluidity).
New dimensions, new effects to explore
Until now, supersolid states in quantum gases have only ever been observed as a string of droplets (along one dimension). The recent Innsbruck-Hannover collaboration has now extended this phenomenon to two dimensions, giving rise to systems with two or more rows of droplets. This is not only a quantitative improvement, but also crucially broadens the research perspectives. For example, in a two-dimensional supersolid, one can study how vortices form in the hole between several adjacent droplets. These vortices described in theory have not yet been demonstrated, but they represent an important consequence of superfluidity. The experiment now reported in the journal Nature creates new opportunities to further investigate the fundamental physics of this fascinating state of matter.
New research field: Supersolids
Predicted 50 years ago, supersolidity with its surprising properties has been investigated extensively in superfluid helium. However, after decades of theoretical and experimental research, a clear proof of supersolidity in this system was still missing. Two years ago, research groups in Pisa, Stuttgart and Innsbruck independently succeeded for the first time in creating so-called supersolids from magnetic atoms in ultracold quantum gases. The basis for the new, growing research field of supersolids is the strong polarity of magnetic atoms, whose interaction characteristics enable the creation of this paradoxical quantum mechanical state of matter in the laboratory.
Among others, the research was financially supported by the Cluster of Excellence QuantumFrontiers and the European Union.
Original publication
Two-dimensional supersolidity in a dipolar quantum gas
Matthew A. Norcia, Claudia Politi, Lauritz Klaus, Elena Poli, Maximilian Sohmen, Manfred J. Mark, Russell Bisset, Luis Santos, and Francesca Ferlaino
Nature 596, 357–361 (2021).
Further information on the research group of Luis Santos: A2 - Many-Body Interacting Quantum Systems
