Local shot noise spectroscopy with scanning tunneling microscopy (STM) has proven to be a powerful technique to investigate the electronic properties of quantum materials. It provides direct and non-invasive insight into the tunneling charge quanta or dynamics at the atomic scale. Due to the typically weak noise signal and the presence of low frequency spurious noise, local noise experiments require a high-resolution measurement amplifier. Here, we present a newly developed high-resolution noise amplifier that we implemented in three different STMs. Compared to our previous generation, we obtain more than a 20-fold improvement in the noise resolution, allowing us to resolve values of the effective charge as small as 0.01 e. Our amplifier opens new possibilities for studying electronic properties in novel materials such as d-wave superconductors. In addition to this, it can give direct information about the local electron temperature in STM experiments.

Bogoliubov quasiparticles play a crucial role in understanding the behavior of a superconductor and in achieving reliable operations of superconducting quantum circuits. Diagnosis of quasiparticle poisoning at the nanoscale provides invaluable benefits in designing superconducting qubits. Here, we use scanning tunneling noise microscopy to locally quantify quasiparticles by measuring the effective charge. Using the vortex lattice as a model system, we directly visualize the spatial variation of the quasiparticle concentration around superconducting vortices, which can be described within the Ginzburg-Landau framework. This shows a direct, noninvasive approach for the atomic-scale detection of relative quasiparticle concentration as small as 10⁻⁴ in various superconducting qubit systems. Our results alert of a quick increase in quasiparticle concentration with decreasing intervortex distance in vortex-based Majorana qubits.