QSE Quantum Seminar: "Anomalous Frequency Shift in Low-Loss Superconducting Granular Aluminum Resonators"

Please join us for the QSE Center Quantum Seminar with Patrick Winkel from Alice & Bob who will give the talk "Anomalous Frequency Shift in Low-Loss Superconducting Granular Aluminum Resonators" on Thursday July 30th from 12:30 to 14:00.
Location: CE 1 103

Pizzas will be available at 12:00. All are welcome to join.

TITLE: "Anomalous Frequency Shift in Low-Loss Superconducting Granular Aluminum Resonators"

Superconducting high-kinetic inductance materials like granular aluminum (grAl) are a versatile part of the circuit quantum electrodynamics (cQED) toolbox. To further advance the use of grAl in quantum devices, it is indispensable to identify the dominant loss mechanisms. The standard approach pairs electromagnetic simulations of resonator geometry with measured temperature and power dependence of resonance frequency and loss rate. Most materials follow the phenomenological theory of two-level systems (TLSs) at low temperatures, resulting in an initial decrease of the resonance frequency with increasing temperature. In my presentation, I will report on the observation of an opposite behavior at the lowest temperatures in our devices: The resonance frequency initially increases with both temperature and readout power, contradicting the standard TLS model predictions. Part of the data can be explained by an alternative mechanism associated with the effect of superconducting quasiparticles in a granular system with a spatially-nonuniform gap. Yet, the observed change in the resonance frequency with temperature is not matched by a proportional change in the loss rate. 

BIO: 
Patrick Winkel completed his PhD in Physics at KIT under the supervision of Prof. Ioan Pop and Prof. Wolfgang Wernsdorfer From 2016 to 2020. He then worked as a postdoctoral researcher in Prof. Pop’s group at KIT from 2020 to 2021, followed by a postdoctoral position with Prof. Robert Schoelkopf at Yale University from 2022 to 2024. Since 2025, he has been working as a Senior Team Lead at Alice & Bob.