CMT178

Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting qubits

• Author(s): Kamal R. Joshi, Sunil Ghimire, Makariy A. Tanatar, Amlan Datta, Jin-Su Oh, Lin Zhou, Cameron J. Kopas, Jayss Marshall, Josh Y. Mutus, Julie Slaughter, Matthew J. Kramer, James A. Sauls, Ruslan Prozorov
• Journal: Physical Review Applied, 20, 024031 (2023) [DOI] [arXiv]
• Abstract: Niobium thin films on silicon substrate used in the fabrication of superconducting qubits have been characterized using scanning and transmission electron microscopy, electrical transport, magnetization, quasiparticle spectroscopy, and real-space real-time magneto-optical imaging. We study niobium films to provide an example of a comprehensive analytical set that may benefit superconducting circuits such as those used in quantum computers. The films show outstanding superconducting transition temperature of Tc=9.35 K and a fairly clean superconducting gap, along with superfluid density enhanced at intermediate temperatures. These observations are consistent with the recent theory of anisotropic strong-coupling superconductivity in Nb. However, the response to the magnetic field is complicated, exhibiting significantly irreversible behavior and insufficient heat conductance leading to thermo-magnetic instabilities. These may present an issue for further improvement of transmon quantum coherence. Possible mitigation strategies are discussed.

• Comment: 8 pages, 5 figures

Return to index