Berlin 2012 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 33: Superconductivity, Measuring Devices, Matter at Low Temperature: Poster Session

TT 33.47: Poster

Mittwoch, 28. März 2012, 15:00–19:00, Poster B

Influence of mechanical strain on coherent atomic tunneling systems investigated by Josephson phase qubits — •Torben Peichl¹, Grigorij J. Grabovskij¹, Jürgen Lisenfeld¹, Georg Weiss^1,2, and Alexey V. Ustinov^1,2 — ¹Physikalisches Institut, KIT, 76131 Karlsruhe — ²DFG Centrum für Funktionelle Nanostrukturen, KIT, 76131 Karlsruhe

Forty years ago Zeller and Pohl discovered a fundamental difference of the heat capacity of glassy materials compared to their crystalline counterparts. Only one year later Anderson, Halperin and Varma attributed this behavior to two-level systems (TLSs), which are formed by the two lowest energy states of atoms tunneling in a double-well potential. This idea was the basis for the so-called tunneling model which despite its totally empiric nature proved to be very successful in describing the universal properties of dissordered materials at temperatures below 1 K. --- It is believed that those TLSs also present in the thin disordered oxide barrier of Josephon junctions, used e.g. in the design of phase qubits, are the main reason for decoherence and thus limit the lifetime of the macroscopic quantum state.

Here we present a method that for the first time allowed the investigation of individual coherent atomic TLSs. We apply strain by in situ bending the chip with the phase qubits and studying the so-called ``avoided-level-crossings'' in the qubit spectrum that are caused by the resonant coupling between the phase eigenstates and coherent TLSs. As a result we can extract their properties that are in good agreement with the tunneling model.