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

• URL: http://arxiv.org/abs/2207.11616v1
• Date: Sat, 23 Jul 2022 22:45:23 GMT
• Title: Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting transmon qubits
• Authors: 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
• Abstract summary: Niobium thin films on silicon substrate used in the fabrication of superconducting qubits have been characterized. The films show outstanding superconducting transition temperature of $T_c=9.35$ K and a fairly clean superconducting gap. The response to the magnetic field is complicated, exhibiting significantly irreversible behavior and insufficient heat conductance.
• Score: 4.281703940559505
• License: http://creativecommons.org/licenses/by/4.0/
• 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 $T_{c}=9.35$ 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.

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