Dresden 2020 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 31: Superconducting Electronics: SQUIDs, Qubits, Circuit QED, Quantum Coherence and Quantum Information Systems 1

TT 31.1: Vortrag

Mittwoch, 18. März 2020, 09:30–09:45, HSZ 03

Shining new light on long standing questions: Recent insights into the understanding of low frequency excess flux noise — •Anna Ferring-Siebert, Fabian Kaap, Andreas Fleischmann, Christian Enss, and Sebastian Kempf — Kirchhoff-Institute for Physics, Im Neuenheimer Feld 227, 69120 Heidelberg, Germany.

Low frequency excess flux noise (LFEFN), which scales as 1/fα, strongly impairs the performance of superconducting quantum devices (SQDs) such as SQUIDs and Qubits. Although it was believed for quite a long time that its magnitude √SΦ and exponent α are fairly independent of the device material and inductance, there meanwhile exist hints for the contrary. It is also known that LFEFN somehow depends on the equipment used for device fabrication, but the reason for that remained unknown up to now.
In this contribution, we first discuss the origin of fabrication induced LFEFN as well as means to minimize it. In particular, we show that commercial deposition equipment often yield material layers containing magnetic impurities causing LFEFN. Whithin this context, we further present how we modified commercial sputter sources to reduce LFEFN as well as indications for a correlation between the LFEFN amplitude and the dc-magnetization of deposited material layers. Finally, we discuss recent measurements investigating the dependence of LFEFN on device inductance suggesting that energy sensitivity rather than magnetic flux noise is the more appropriate figure of merit for describing LFEFN.

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