A freshly polished niobium surface shines like a mirror. But within minutes, a dull oxide film, invisible to the eye, forms on it. For a superconducting qubit, this film is like sand in an hourglass: it causes the quantum state to decay prematurely. The longer a qubit 'breathes' air, the faster it forgets its quantum information.

Scientists made a clever move: they built a small sealed chamber where the device is placed immediately after removing the oxide. Just five minutes, and the device is already in a vacuum, where the film has nothing to grow from. This 'vacuum incubator' allowed niobium resonators to achieve an internal quality factor above one million at single-photon power. That means the signal inside the resonator lives for a very long time, barely decaying.

Then the researchers deliberately returned the devices to air. The resonator frequency drifted downward, and the quality factor dropped — exactly as predicted by the oxide growth model. This confirmed that it is indeed the metal-air interface that steals coherence. Now there is a way to keep this interface under control and, at the same time, study how quickly the oxide returns and how it affects the quantum properties of niobium.