Regensburg 2025 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 11: Superconductivity: Poster

TT 11.29: Poster

Montag, 17. März 2025, 15:00–18:00, P4

High-quality niobium Josephson junctions for superconducting mm-wave qubits — •Urs Strobel¹, Benedict Rothmund¹, Lucas Radke¹, Hannes Rotzinger^1,2, and Alexey V. Ustinov^1,2 — ¹Physikalisches Institut (PHI), Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany — ²Institut for Quantum Materials and Technologies (IQMT), Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany

Millimeter-wave quantum circuits require a superconductor with an energy gap above 100 GHz , which exceeds the energy gap of the widely used aluminum. Niobium offers much more suitable properties in this frequency range. Implemented in thin film technology on low loss substrates, high quality niobium Josephson junctions should complement the capacitors and inductors required for quantum circuits. We have developed Nb/Al-AlO_x/Nb trilayer Josephson junctions suitable for quantum circuits and characterized them at cryogenic temperatures. We present dc and mm-wave measurement data obtained with these junctions. In addition, we discuss design considerations for prospective mm-wave transmon qubits.

Keywords: Superconductivity; Josephson junction; Qubit; mm-Wave