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Physicists created the very first two-dimensional supersolid – a strange phase of matter which behaves as both a solid and a frictionless liquid.
Supersolids are materials whose atoms are arranged in a regular and repeating crystal structure, but are also able to flow indefinitely without ever losing kinetic energy. Despite their strange properties, which seem to violate many known laws of physics, physicists have long predicted them theoretically – they first appeared as a suggestion in the work of physicist Eugene Gross as early as 1957.
Now, using lasers and super-refrigerated gases, physicists have finally coaxed a supersolid into a 2D structure, a breakthrough that could allow scientists to uncover the deeper physics behind the mysterious properties of matter’s eerie phase.
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The researchers are particularly interested in how their 2D supersolids will behave when they spin in a circle, alongside the tiny whirlpools, or vortices, that will appear inside them.
“We expect that there will be a lot to learn from studying rotational oscillations, for example, as well as vortices that can exist in a 2D system much more easily than in 1D,” said the author. principal Matthew Norcia, physicist at the Institute for Quantum, University of Innsbruck. Optics and Quantum Information (IQOQI) in Austria, Live Science said in an email.
To create their supersolid, the team hung a cloud of dysprosium-164 atoms inside the optical tweezers before cooling the atoms to just above zero Kelvin (minus 459.67 degrees Fahrenheit, or minus 273.15 degrees Celsius) using a technique called laser cooling.
Shooting a laser at a gas usually heats it up, but if the photons (light particles) in the laser beam move in the opposite direction to the moving gas particles, they can actually slow down and cool the gas particles. After cooling the dysprosium atoms to the maximum with the laser, the researchers loosened the “grip” of their optical tweezers, creating just enough space for the more energetic atoms to escape.
Because “hotter” particles move faster than cooler ones, this technique, called evaporative cooling, left researchers with only their supercooled atoms; and these atoms had been transformed into a new phase of matter – a Bose-Einstein condensate: a collection of atoms that have been supercooled within a hair’s breadth of absolute zero.
When a gas is cooled to a temperature close to zero, all of its atoms lose their energy and enter the same energy states. Since we can only distinguish the otherwise identical atoms in a gas cloud by examining their energy levels, this equalization has a profound effect: quantum mechanical point of view, perfectly identical.
It opens the door to some really strange things quantum effects. A key rule of quantum behavior, Heisenberg’s Uncertainty Principle, says that you cannot know both the position and momentum of a particle with absolute precision. Yet now that the Bose-Einstein condensate atoms are no longer moving, their full momentum is known. This leads to the positions of atoms becoming so uncertain that the places they could possibly occupy become larger than the spaces between the atoms themselves.
Instead of discrete atoms, the overlapping atoms in the Bose-Einstein fuzzy condensate ball act as if they are just one giant particle. This gives some Bose-Einstein condensates the property of superfluidity – allowing their particles to flow without any friction. In fact, if you stir a cup of superfluid Bose-Einstein condensate, it would never stop swirling.
The researchers used dysprosium-164 (an isotope of dysprosium) because it (along with its neighbor on the periodic table Holmium) is the most magnetic of all the elements discovered. This means that when the dysprosium-164 atoms were supercooled, in addition to becoming a superfluid, they also clumped together into droplets, sticking to each other like small magnetic bars.
By “carefully adjusting the balance between long-range magnetic interactions and short-range contact interactions between atoms,” Norcia said, the team was able to create a long, one-dimensional tube of droplets that also contained free-flowing atoms. – a 1D supersolid. It was their previous job.
To go from a 1D supersolid to a 2D supersolid, the team used a larger trap and lowered the intensity of their tweezers optical beams in two directions. This, in addition to keeping enough atoms in the trap to maintain a sufficiently high density, ultimately allowed them to create a zigzag structure of droplets, similar to two staggered 1D tubes sitting next to each other, a 2D supersolid.
With the task of its creation behind them, physicists now want to use their 2D supersolid to study all the properties that emerge from this extra dimension. For example, they plan to study the vortices that emerge and get trapped between droplets in the lattice, especially since these swirling atomic vortices, at least in theory, can spiral indefinitely.
It also brings researchers closer to the loose 3D supersolids envisioned by early proposals like Gross’s, and even more alien properties they may have.
The researchers published their results on Aug. 18 in the journal Nature.
Originally posted on Live Science.
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