After 40 years on paper, a quantum 'energy ladder' finally shows up in the lab

Back in 1984, theory predicted that matter at a tipping point — like water at the boil — absorbs energy in neat, fixed steps, like rungs on a ladder. No one had ever seen those rungs. A Caltech-led team now has, using a chain of up to 35 strontium atoms held by laser light as a small quantum simulator: the steps matched the predictions at two different tipping points. The same trick can now be pointed at quantum puzzles where no one yet knows the answer.