Implementing Josephson Junction spectroscopy in a scanning tunneling microscope

Josephson junction spectroscopy (JJS) is a powerful local microwave spectroscopy technique that has promising potential as a diagnostic tool to probe the microscopic origins of noise in superconducting qubits. In this talk I will present progress towards realizing JJS in a scanned geometry, where the Josephson junction (JJ) is formed between a superconducting sample and a high capacitance superconducting STM tip. I will first present data from planar Nb-based JJs that demonstrates the benefits of including a high capacitance shunt across the JJ, which improves spectral resolution. It will then be shown how an equivalent circuit can be implemented by utilizing a planarized STM tip with local prominences, which is fabricated via electron beam lithography and reactive ion etching, followed by coating with a superconducting layer. I will then show the results of initial measurements that utilize these high capacitance tips to probe Niobium Nitride (NbN) substrates, and I will discuss the effects of different circuit geometries (i.e. preamp and filter choice) on those measurements. Finally, calculations will be shown that estimate the sensitivity and spectral resolution of this scanned JJS technique.