InstituteQ Visitor’s Talk: Sebastian de Graaf of the National Physical Laboratory (UK)

Sebastian de Graaf of the National Physical Laboratory (UK) is a frequent collaborator with both VTT Technical Research Centre of Finland and Aalto University. His work with these groups covers topics related to superconducting qubits, two-level systems, quantum transport experiments, and quantum electrical metrology.

Sebastian will provide a talk on February 10, titled “In-situ materials characterisation of defects present in superconducting quantum circuits.”

When: 12:30-14:00 on 10.02.2025
Where: R036/2191 Pieni Sali, Micronova, Tietotie 3, 02150 Espoo
Additional information: No registration necessary, free to attend

From Sebastian, what will your talk discuss?

Superconducting quantum circuits, and qubits in particular, suffer from material defects that cause noise, decoherence, and parameter instability – significantly hampering the development of large-scale quantum circuits. Understanding the origins of these material defects, and thereafter finding ways to mitigate them to improve device coherence is becoming a more and more urgent challenge for the field. While the vast repertoire of materials science tools available today are extremely powerful in obtaining structural and chemical information of materials, they lack the energy resolution and sensitivity to directly correlate such information with what is observed to hamper the performance of qubits. New techniques that bridges in situ defect detection with chemical and structural information accessible by modern materials science tools are thus required.

I will describe recent work on the development of several such new techniques based on in situ device measurements. This includes mK scanning probe microscopy for imaging individual two-level system (TLS) defects in live circuits, in situ electron spin resonance (ESR) techniques revealing the chemical nature of spurious surface spins, as well as in situ manipulation of the chemical environment through quantum fluid immersion cooling. How such new techniques need to work hand-in-hand with established materials science to optimise materials and device coherence will be discussed.