A team of researchers has produced vortices within a supersolid, confirming superfluid behavior within this state of matter.
As well as all the states of matter you learned about in school – solids, liquids, and gases – there are plasmas, time crystals, Bose-Einstein condensates, and superfluids. Adding to an already long list are supersolids.
When a gas of bosons – particles or atoms that have integer spin and are described by Bose-Einstein statistics – is cooled to temperatures approaching absolute zero, the bosons form a single quantum object, often compared to acting like a single atom, known as Bose-Einstein Condensate (BEC).
“The wave function of a BEC corresponds to the ground state of a macroscopic quantum object,” one paper explains. “In other words, a collection of atoms in a BEC behaves as a single quantum entity.”
In this strange new state of matter, first created in the real world in 1995, you get a macroscopic look at quantum behavior, including superfluidity – where flow takes place without loss of kinetic energy – and the formation of quantum vortices.
Supersolid states of matter have been predicted for decades, but were only recently synthesized in the lab. In this state, produced by manipulating quantum gases, matter acts as a solid but also display superfluid properties.
“It is a bit like Schrödinger’s cat, which is both alive and dead, a supersolid is both rigid and liquid,” Francesca Ferlaino, from the Department of Experimental Physics at the University of Innsbruck and the Institute of Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences (ÖAW), explained in a statement.
The team successfully created a long-lived, two-dimensional supersolid in 2021 by manipulating an ultracold gas of erbium atoms, forming it into a supersolid.
“The next step – developing a way to stir the supersolid without destroying its fragile state – required even greater precision,” lead author Eva Casotti said.
In the new research, the scientists used magnetic fields to carefully rotate a supersolid. Just like in superfluids, they observed the formation of quantized vortices within the supersolid.
“Rotating fluids on all scales exhibit a whirling motion known as vorticity. Unique to the quantum world, however, is the quantization of this rotation owing to the single-valued and continuous nature of the underlying macroscopic wavefunction,” the team explains in their study. “Observing quantized vortices is considered as unambiguous evidence of superfluidity, relevant for a wide variety of interacting many-body quantum systems”.
While adding evidence that supersolids have superfluid properties to them, the study could also be applicable to a wide range of areas.
“Our findings open the door to studying the hydrodynamic properties of exotic quantum systems with multiple broken symmetries, such as quantum crystals and even neutron stars,” Thomas Bland, who guided the theoretical development of the project, added.
“For instance, it is assumed that the change in rotational speed observed in neutron stars – so-called glitches – are caused by superfluid vortices trapped inside neutron stars. Our platform offers the opportunity to simulate such phenomena right here on Earth. Superfluid vortices are also believed to exist in superconductors, which can conduct electricity without loss. “
The study is published in Nature.
