A tiny cloud of atoms, cooled to millionths of a degree above absolute zero, floats in a ring-shaped trap. It looks like a glowing necklace, but physicists have made it live on the surface of an invisible bagel.

Using laser beams and microwave pulses, three internal states of the atoms were linked into a cycle. It's as if three roads were closed into a loop, and an atom could move from one to the next until it returned to the start. This hidden loop, together with the real ring, forms a torus — the surface of a bagel. Magnetic flux flows through this torus and leaves its mark: the density of atoms in the ring becomes wavy, with peaks and troughs.

The number of waves is strictly set by quantum rules — a hallmark of the torus's geometry. By changing the coupling phase between states, the researchers shifted the waves, as if rolling a pattern around the bagel. This reveals an effect similar to charge pumping in microelectronics, but here, instead of electrons, it's the atoms themselves.

The experiment started with a cylinder: atoms moved around the ring, but the hidden loop was not yet closed. When the cycle was closed, the cylinder became a torus, and density waves emerged on their own. This is the first time the quantum Hall effect has been reproduced on an artificially curved space.

Such atomic 'bagels' could become a laboratory for testing ideas about how matter behaves in curved worlds. Perhaps this is how we can simulate conditions near black holes or in the early universe.