Tunable Nb Superconducting Resonator Based on a Constriction Nano-SQUID Fabricated with a Ne Focused Ion Beam

Tunable resonators with high quality factors underpin the storage and retrieval of microwave-domain quantum information in spin ensembles used as long-lived quantum memories, and can enable multifrequency high-sensitivity electron spin resonance (ESR). The authors develop a single-layer technology, based on embedding nanoSQUIDs in superconducting niobium resonators, to realize high-quality frequency-tunable devices that are resilient to moderate magnetic fields. These devices will enable tunable-resonator-enhanced ESR protocols to be performed at specific fields and frequencies, such as storing quantum information in spins at low-decoherence ``clock transitions''.