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TT: Fachverband Tiefe Temperaturen

TT 16: Poster Session Superconductivity, Cryogenic Particle Detectors, Cryotechnique

TT 16.32: Poster

Montag, 16. März 2020, 15:00–19:00, P2/EG

Investigation of the influence of nuclear spins and hydrogen absorbates on low-frequency excess flux noise — •Fabian Kaap, Anna Ferring-Siebert, Christian Enss, and Sebastian Kempf — Kirchhoff-Institute for Physics, Im Neuenheimer Feld 227, 69120 Heidelberg, Germany

The performance of superconducting quantum devices (SQDs) such as SQUIDs or qubits often suffers from low frequency excess flux noise (LFEFN). It is widely accepted that spin fluctuations at the surface of the superconductor, e.g. caused by adsorbed oxygen or hydrogen, is one of many sources of LFEFN. Recent works also suggest that spin fluctuations inside the bulk superconductor, e.g. due to nuclear spins, could give rise to LFEFN. However, there have been no experimental proofs or hints confirming or excluding these predictions so far.

In this contribution, we first present a chemical method to load hydrogen inside Nb layers in a controllable manner. We then discuss if and how LFEFN depends on hydrogen loading present in the bulk of the SQUID loop. Finally, we discuss our experimental approach to investigate the influence of device material on the LFEFN to ultimately reveal whether or not nuclear spins is another source of LFEFN. Within this context, we compare measurements on dc-SQUIDs with SQUID-washer made of Al to our conventional Nb-based SQUIDs.