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TT: Fachverband Tiefe Temperaturen

TT 37: Superconducting Electronics: SQUIDs, Qubits, Circuit QED

TT 37.11: Vortrag

Freitag, 9. September 2022, 12:15–12:30, H22

Magnetic 1/f noise in superconducting microstructures and the fluctuation-dissipation theorem — •M. Herbst, A. Fleischmann, L. Gastaldo, D. Hengstler, L. Münch, A. Reifenberger, C. Ständer, and C. Enss — Uni Heidelberg

The performance of superconducting devices like SQUIDs and qubits is often limited by 1/f-noise and finite coherence times. Various types of slow fluctuators in the Josephson-junctions and in the passive parts of these superconducting circuits can cause such noise, and devices most likely suffer from a combination of different noise sources, which are hard to disentangle and therefore hard to eliminate. Magnetic flux noise caused by fluctuating magnetic moments of magnetic impurities or dangling bonds in superconducting inductances, surface oxides, insulating oxide layers and adsorbates should be a very likely contribution in many cases. We present an experimental setup to measure at Millikelvin temperatures both, the complex impedance of superconducting micro-structures as well as the magnetic flux noise that is picked-up by these structures. This allows for very important sanity checks by connecting both quantities via the fluctuation-dissipation-theorem. In order to allow for state-of-the-art sensitivity in both experiments, the structures under investigation are part of a Wheatstone-like bridge, read-out by two cross-correlated independent dc-SQUID readout chains. We present measurements of the insulating SiO2 layers of our devices, the superconducting structures themselves, and magnetically doped noble-metal layers in the vicinity of the pickup coils at T = 20-800mK and f=100mHz-100kHz.