In the quantum world, particles can merge into a single liquid that flows without friction. One of its most mysterious forms is the fractional quantum Hall liquid. In it, electrons or atoms move as a single vortex, and their charge splits into fractions, like a pie cut into perfectly equal slices. But preparing such a liquid in the lab is like trying to assemble a puzzle where every piece is afraid of being touched.

Usually, scientists take a cloud of cooled atoms and try to coax them into the right order. The problem is that the system passes through dangerous states where order easily collapses. The authors of the new study devised a workaround. They propose starting with a completely empty trap and adding atoms one by one, using laser beams with a twisted profile, so-called Laguerre-Gaussian beams. These beams act like a funnel that pulls atoms from a large reservoir (a Bose-Einstein condensate) and places them onto the desired orbits with precise angular momentum.

The method was tested in numerical simulations for dozens of particles — more than current experiments can handle. The calculations showed that the process remains stable if the atoms are held not by a simple flat bowl but by a trap with a slight distortion (an anharmonic addition). Without it, the atoms started to clump together, and the liquid didn't form. This trick is reminiscent of how a slight unevenness at the bottom of a glass prevents water from spinning too fast and splashing out.