Tapping-mode SQUID-on-tip microscopy for materials research and quantum chip diagnostics

The performance of quantum chips and the physics of quantum materials and are often dominated by local properties. Understanding those local properties requires microscopy that operates at cryogenic temperatures and that does not disturb the highly sensitive quantum effects it aims to reveal. In this talk, we will introduce a scanning-probe microscope that combines tapping-mode atomic force microscopy (AFM) with a nano-SQUID “on-tip” (SOT) sensor made from proximity Josephson junctions [1]. This design enables extremely short sensor-chip distances and robust height feedback to prevent crashes. It offers a non-invasive, purely electronic, laser-free readout, as well as in-plane and out-of-plane magnetic sensitivity. Frequency multiplexing of the nanoSQUID output permits simultaneous imaging of chip topography, magnetic fields, current flow and thermal dissipation on the nanoscale. We will show experiments from this novel microscope on magnetic and superconducting nanostructures, as well as spin qubits and transmon quantum chips. For the latter two, we demonstrate how insights from this SQUID microscopy into material properties and local effects can be used to improve the quantum chips.

[1]         M. Rog et al. arXiv:2508.21575 (2025)