Dresden 2014 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 30: Superconductivity - Poster Session

TT 30.60: Poster

Monday, March 31, 2014, 15:00–19:00, P2

Probing the Interaction of Individual Two-Level-Systems with Quasiparticles using a Superconducting Qubit — •Alexander Bilmes, Jürgen Lisenfeld, Georg Weiss, and Alexey V. Ustinov — Physikalisches Institut, Karlsruhe Institute of Technology and DFG-Center for Functional Nanostructures (CFN), D-76128 Karlsruhe, Germany

Two-Level-Systems (TLS) are solid state defects which constitute one of the main sources of decoherence in a variety of nanoscale devices while their physical nature remains yet unclear. TLS couple to the environment via their electrical dipole moment and the mechanical strain field. It is possible to use a superconducting phase qubit for coherent manipulation and measurement of TLS which reside inside the tunnel barrier of the qubit’s Josephson junction. In order to verify theoretical TLS models, we investigate whether TLS interact with quasiparticles (QP) existing in the qubits circuit. We use an on-chip DC-SQUID to generate QP in-situ. The QP density can be calibrated according to their effect on the phase qubit, where they give rise to a change in energy relaxation time and plasma frequency as has been shown by the group of J.M. Martinis [1]. Here we present first results on the coherence of individual TLS in dependence of TLS asymmetry and QP density. We observe a strong enhancement of the TLS energy relaxation rate by injected QP.
J. Wenner et al., Phys. Rev. Lett. 110, 150502 (2013)