Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 16: Transport: Quantum Coherence and Quantum Information Systems – Experiments (jointly with HL, MA)

TT 16.9: Talk

Monday, March 16, 2015, 17:00–17:15, H 0110

Incoherent Two-Level Fluctuators inside the Josephson junction of a Superconducting Qubit — •Saskia Meißner, Jürgen Lisenfeld, Alexey V. Ustinov, and Georg Weiß — Physikalisches Institut, KIT Karlsruhe

Spectroscopy on qubits based on Josephson junctions reveals the precence of defects like quantum coherent tunneling systems (TS) as well as two-level fluctuators (TLF). TLF are incoherent tunneling particles which are described by dissipative quantum tunneling theory. Due to the coherent interaction of qubit and the TS, it is possible to probe individual TLF that themselves are coupled to a tunneling system.

Here we perform high resolution defect spectroscopy by tuning the TS and TLF asymmetry energies with external strain applied to the qubit chip. Slow fluctuators induce telegraph noise in the resonance frequency of TS. Fast fluctuators create double resonances of TS in the manner of two frequency branches. Apparently, the two-level fluctuator causes a rapid modulation of the asymmetry energy of the tunneling system on top of the static strain tuning. We perform time domain analyses of TS resonance frequencies with the goal of reconstructing the TLF deformation potential and the TLF-TS interaction potentials.