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TT: Fachverband Tiefe Temperaturen

TT 48: Superconductivity: Tunnelling, Josephson Junctions, SQUIDs 2

TT 48.6: Vortrag

Mittwoch, 22. März 2017, 16:30–16:45, HSZ 201

Recent insights in low-frequency excess flux noise of superconducting quantum devices — •Sebastian Kempf, Anna Ferring, David Uhrig, Andreas Fleischmann, and Christian Enss — Kirchhoff-Institute for Physics, Heidelberg University, Im Neuenheimer Feld 227, 69120 Heidelberg, Germany.

Low-frequency excess flux noise strongly diminishes the performance of flux-sensitive superconducting quantum devices. It limits, for example, the coherence time of flux and phase qubits and makes SQUID based measurements of low-frequency signals challenging. Recent experiments suggest that low-frequency excess flux noise in Josephson junction based devices originates from the random reorientation of interacting spins located in surface layer oxides or in the interface between the substrate and the device wiring. Though this explanation proves to be generally correct, the physical nature of these spins, i.e. their origin as well as their interaction mechanisms, has not be been resolved so far and many questions remain.

In this contribution we present a comprehensive analysis of low-frequency excess flux noise. Our analysis include 373 individual noise spectra that were taken from 84 superconducting quantum devices at temperatures below 1 K. It revealed an evidence for a material and device type dependence of low-frequency excess flux noise and showed that SQUID arrays systematically feature higher noise exponents than single SQUIDs. This somehow facilitates to engineer the shape of magnetic flux noise spectra by choosing a proper device material and type.