For the first time, scientists have observed the iconic Shapiro steps, a staircase-like quantum effect, in ultracold atoms.
In a recent experiment, an alternating current was applied to a Josephson junction formed by atoms cooled to near absolute zero and separated by an extremely thin barrier of laser light. Remarkably, the atoms were able to cross this barrier collectively and without energy loss, behaving as if the barrier were transparent, thanks to quantum tunneling.
As the oscillating current flowed through the junction, the difference in chemical potential between the two sides did not change smoothly, but instead increased in discrete, evenly spaced steps, like climbing a quantum staircase. The height of each step is directly determined by the frequency of the applied current, and these step-like chemical potential differences are the atomic analog of Shapiro steps in conventional Josephson junctions.








