Loss Mechanisms and Quasiparticle Dynamics in Superconducting Microwave Resonators Made of Thin-Film Granular Aluminum
Abstract
Superconducting high kinetic inductance elements constitute a valuable resource for quantum circuit design and millimeter-wave detection. Granular aluminum (grAl) in the superconducting regime is a particularly interesting material since it has already shown a kinetic inductance in the range of nH /□ and its deposition is compatible with conventional Al /AlOx /Al Josephson junction fabrication. We characterize microwave resonators fabricated from grAl with a room temperature resistivity of 4 ×103 μ Ω cm , which is a factor of 3 below the superconductor to insulator transition, showing a kinetic inductance fraction close to unity. The measured internal quality factors are on the order of Qi=105 in the single photon regime, and we demonstrate that nonequilibrium quasiparticles (QPs) constitute the dominant loss mechanism. We extract QP relaxation times in the range of 1 s and we observe QP bursts every ∼20 s . The current level of coherence of grAl resonators makes them attractive for integration in quantum devices, while it also evidences the need to reduce the density of nonequilibrium QPs.
- Publication:
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Physical Review Letters
- Pub Date:
- September 2018
- DOI:
- 10.1103/PhysRevLett.121.117001
- arXiv:
- arXiv:1802.01858
- Bibcode:
- 2018PhRvL.121k7001G
- Keywords:
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- Condensed Matter - Superconductivity
- E-Print:
- 5 pages, 4 figures, supplementary material