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arXiv · 2410.03009

Implementing Josephson Junction spectroscopy in a scanning tunneling microscope

Margaret A. Fortman·David C. Harrison·Ramiro H. Rodriguez·Zachary J. Krebs·Sangjun Han·Min Seok Jang·Robert McDermott·Caglar O. Girit·Victor W. Brar
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Abstract

Josephson junction spectroscopy 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. We present advancements toward realizing Josephson junction spectroscopy in a scanning geometry, where the Josephson junction is formed between a superconducting sample and a high capacitance superconducting STM tip. Data from planar Nb-based Josephson junction devices first demonstrate the benefits of including a high capacitance shunt across the junction, which decreases linewidth and improves performance at elevated temperatures. We show how an equivalent circuit can be implemented by utilizing a planarized STM tip with local prominences, which are fabricated via electron beam lithography and reactive ion etching, followed by coating with a superconducting layer. Differential conductance measurements on a superconducting NbN surface demonstrate the ability of these high capacitance tips to decrease both thermal noise and P(E)-broadening in comparison to typical wire tips.

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Margaret A. Fortman, David C. Harrison, Ramiro H. Rodriguez, Zachary J. Krebs, Sangjun Han, Min Seok Jang, Robert McDermott, Caglar O. Girit, Victor W. Brar. 2024-10-03. Implementing Josephson Junction spectroscopy in a scanning tunneling microscope. https://arxiv.org/abs/2410.03009

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