A crowd of people in a subway station moves slower than individuals: everyone gets in everyone else's way. A similar picture emerges in a dense cloud of magnetic atoms exchanging energy. Previously, it was thought that the transfer rate depended only on the atoms' own properties. It turns out the main brake is mutual detuning: neighboring atoms shift each other's energy levels, and only those pairs whose shifts match can exchange energy.
This is like two people wanting to toss a ball, but each stands on a different step of a staircase. If the steps are the same height, the throw is easy. If not, the ball won't make it. In the atomic world, energy levels play the role of steps. When atoms are tightly packed, their levels shift differently, and only a small fraction of pairs remain "on the same step." So energy doesn't flow as a continuous stream but in rare jumps.
The scientists derived a simple rule: the energy transfer time grows with distance not as a square but much faster, as distance to the power of 4.5 in bulk samples. In flat (two-dimensional) atomic layers, the dependence is different — power 3. Both numbers follow from the same idea of accumulating detunings. This allows more accurate predictions for superradiant lasers, where such atomic ensembles are used as light sources.
So the disorder in the atomic crowd is not just chaos. It follows a strict law that can now be written as a single formula.
In dense atomic ensembles, energy can be transferred resonantly, like a tuning fork exciting another tuning fork of the same frequency. But if you place a third tuning fork with a slightly different frequency nearby, the resonance is disrupted: this is how Ising blockade works.