Ultra-cold mini tornadoes of the quantum world at the University of Innsbruck
quantum gases. A team of quantum physicists with the participation of the University of Innsbruck has developed a new method with which vortices in dipolar quantum gases can be observed.
A team of quantum physicists led by three-time ERC award winner Francesca Ferlaino has developed a new method for observing eddies in dipolar quantum gases. These quantum vortices are considered a clear indication of superfluidity, the frictionless flow of a quantum gas, and have now been experimentally demonstrated for the first time at the University of Innsbruck in dipolar gases, according to the university.
On a large scale a tornado, on a small scale in the quantum world
Vortices are omnipresent in nature: whirlpools can be created by stirring. If the atmosphere is stirred up, powerful tornadoes can develop. This is also the case in the quantum world, only that many identical vortices are created there at the same time, it is said – the vortex is “quantized”.
Such quantized vortices have already been detected in many quantum gases. “This is interesting because such vortices are a clear indication of the frictionless flow of a quantum gas – the so-called superfluidity -” says Francesca Ferlaino from the Institute for Experimental Physics at the University of Innsbruck and the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences.
New method creates quantum vortices
Ferlaino and her team are researching quantum gases made up of strongly magnetic elements. For such dipolar quantum gases, in which the atoms interact strongly, the quantum vortices have not yet been detected. The scientists have now developed a new method: “We use the directional dependence of our quantum gas from dysprosium, whose atoms behave like many small magnets, to stir the gas,” explains Manfred Mark from Francesca Ferlaino’s team.
To do this, the scientists apply a magnetic field to their quantum gas in such a way that this initially round, pancake-shaped gas is deformed elliptically due to magnetostriction. The same simple yet effective idea goes back to a theoretical proposal made a few years ago by a Newcastle University theory team led by Nick Parker, which also included Thomas Bland, the co-author of the current paper.
“By rotating the magnetic field, we can rotate the quantum gas,” explains Lauritz Klaus, first author of the work. “If it rotates fast enough, small vortices form in the quantum gas. In this way, the gas tries to balance the angular momentum.” If the rotation speed is high enough, conspicuous stripes with vortices form along the magnetic field. These are a special characteristic of dipolar quantum gases and have now been observed for the first time at the University of Innsbruck.
According to the University of Innsbruck, the illustration shows the density distribution of a rotating dipolar Bose-Einstein condensate with quantized vortices based on simulation data from the work. The vortices, which can be recognized by the density drops, arrange themselves due to the anisotropic, long-range interaction between the atoms (© Ella Maru Studio).
Next goal is supersolidity
The new method, which has now been presented in the journal Nature Physics, is to be used in the future to investigate superfluidity in supersolid states in which quantum matter is both solid and liquid at the same time. “It is still a big open question to what extent the newly discovered supersolid states are actually superfluid, and this question has been very little studied today.” The work (“Observation of vortices and vortex stripes in a dipolar condensate”, Lauritz Klaus, Thomas Bland, Elena Poli, Claudia Politi, Giacomo Lamporesi, Eva Casotti, Russell N. Bisset, Manfred J. Mark and Francesca Ferlaino, Nature Physics 2022) was created in collaboration with Giacomo Lamporesi from the University of Trento and the theorist Russell Bisset from the university Innsbruck and was financially supported by the European Research Council ERC, the Austrian Science Fund FWF and the Austrian Academy of Sciences, among others.