Berlin 2018 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 75: Superconductivity: Mesoscopic Superconductivity and Quantum Circuits

TT 75.6: Talk

Wednesday, March 14, 2018, 17:45–18:00, H 2053

Spectroscopy of Two-Level-Systems in an Xmon Qubit — •Alexander Bilmes¹, Georg Weiss¹, Alexey V. Ustinov^1,2, and Jürgen Lisenfeld¹ — ¹Physikalisches Institut, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany — ²Russian Quantum Center, National University of Science and Technology MISIS, Moscow 119049, Russia

Superconducting quantum circuits are close to fulfilling all criteria to realize a quantum processor. However, a severe coherence-limiting factor are Two-Level-Systems (TLS) that reside in substrate-qubit interfaces or dielectric layers such as surface oxides and the tunnel barrier of the Josephson junction. Since TLS possess an electrical dipole moment, they can couple to the oscillating field of the qubit's circuit, making them an energy sink for the qubit. We exploit this sensitivity of qubits to spectroscopically detect individual TLSs, whose transition frequencies are tuned via applied physical strain and an electrical dc field. This experimental platform enables us to investigate coherence properties of individual TLSs in various quantum circuits and to draw conclusions about their density. Here we present the first strain and dc-field dependent spectroscopy of TLSs obtained with an Xmon sample. Especially, we propose a method to distinguish TLSs hosted in Josephson contacts from surface TLSs.