Regensburg 2013 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 6: Superconductivity: Tunnelling & Josephson Junctions

TT 6.1: Talk

Monday, March 11, 2013, 09:30–09:45, H18

Strain Spectroscopy and Decoherence of Two-Level Systems — •Jürgen Lisenfeld, Grigorij Grabovskij, Georg Weiß, and Alexey V. Ustinov — Physikalisches Institut, Karlsruhe Institut für Technologie (KIT), Karlsruhe

Two-level systems (TLSs) are believed to originate in individual atoms which may tunnel between two metastable positions of a disorderedlattice. Recently, TLSs have been identified as a source of noise and decoherence in nanofabricated devices such as MOSFETs, electromagnetic and nanomechanical resonators, detectors, SQUIDs, and superconducting qubits. Despite this ubiquitous importance, the microscopic nature of TLSs has remained obscure until today and is subject of current debate.

We perform novel experiments which allow us to obtain high-resolution images of the TLS distribution in a Josephson junction's tunnel barrier by operating a superconducting phase qubit as a sensitive TLS detector. Using a piezo actuator, we are able to control the mechanical strain in the sample in-situ and find that it strongly affects the TLS frequency and asymmetry energy. We will present data on the characteristic strain dependence of individual TLS's coherence times. These results are relevant for verification of TLS theoretical models within the long-standing effort of revealing the nature of TLS in disordered solids.