Advancements in Scanning Josephson Junction Spectroscopy

Josephson junction spectroscopy (JJS) is a microwave spectroscopy technique which has demonstrated potential for probing the microscopic origins of noise in superconducting qubits. During this presentation, I will discuss advancements made in the pursuit of implementing JJS within a scanning framework, where the Josephson junction (JJ) is formed between a superconducting sample and a high-capacitance superconducting scanning tunneling microscope (STM) tip. I will present calculations using P(E)-theory that demonstrate the benefits of a large capacitance across the junction, including a narrower microwave linewidth, and decreased sensitivity to leads. It will then be shown how a planarized superconducting STM tip with local prominences is fabricated using electron beam lithography and reactive ion etching. Finally, measurements will be shown that utilize these high capacitance tips to probe Niobium Nitride (NbN) substrates.