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TT: Fachverband Tiefe Temperaturen

TT 13: Quantum Computing (joint session TT/DY)

TT 13.1: Talk

Wednesday, September 29, 2021, 11:15–11:30, H7

Probing the critical current coupling of defects in Josephson junctions — •Alexander Konstantin Neumann¹, Benedikt Berlitz¹, Alexey V. Ustinov^1,2,3, and Jürgen Lisenfeld¹ — ¹Physikalisches Institut, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany — ²National University of Science and Technology MISIS, Moscow 119049, Russia — ³Russian Quantum Center, Skolkovo, Moscow 143025, Russia

Material defects form a major source of decoherence in state of the art superconducting quantum bits. It has been a long standing question whether defects residing in the tunnel barrier of Josephson junctions modify their critical current. We investigate this with spectroscopic measurements and QuTiP simulations on individual defects strongly coupled to a transmon qubit. By observing avoided level crossings at driving amplitudes allowing for multi-photon transitions, we quantify the strength of the critical current coupling. Moreover, we find an effective direct interaction between the defect and the qubit's readout resonator, providing an additional decoherence channel.