with UV light.*

Magnetic flux noise with a 1/f power spectrum is pervasive in superconducting devices, and presents a fundamental limit to both the low-frequency energy resolution of dc SQUIDs and the high-frequency coherence of flux-sensitive superconducting qubits. Studies of the scaling of the magnitude of the flux noise with SQUID geometry are consistent with generation of the noise by fluctuating magnetic dipoles on the superconducting surface. Kumar et al. showed that the magnetic dipoles are adsorbed molecular oxygen, and reduced the noise with processes in a room-temperature hermetic sample enclosure. We demonstrate a factor of about three reduction of the 1/f flux noise power spectrum in Nb SQUIDs by applying 240-nm UV light from a Light Emitting Diode at cryogenic temperatures. Subsequent exposure of the SQUIDs to oxygen at atmospheric temperature and pressure restored the flux noise to its original value. Re-exposure to UV at cryogenic temperatures again reduced the flux noise. These results are consistent with molecular oxygen being the source of the noise. Our work demonstrates a practical technique to reduce the flux noise of superconducting devices in situ.