Regensburg 2004 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 29: Quantenkoh
ärenz und Quanteninformationssysteme II
TT 29.3: Vortrag
Donnerstag, 11. März 2004, 15:00–15:15, H19
Multi-photon transitions and subharmonic-like resonances in a superconducting flux qubit device — •M. Thorwart1,2, S. Saito2, H. Tanaka2, H. Nakano2, M. Ueda2, K. Semba2, and H. Takayanagi2 — 1Institut für Theoretische Physik IV, Heinrich-Heine-Universität Düsseldorf — 2NTT Basic Research Laboratories, Atsugi-shi, Japan
We investigate both experimentally and theoretically the quantum mechanical dynamics of superposition states of a superconducting loop with three Josephson junctions in the presence of an external RF-field. Read-out of the state of this driven macroscopic quantum two-state system is performed by an additional dc-SQUID. For strong enough driving, we find up to three-photon transitions in spectroscopy measurements. The width of the n-photon resonance scales with the n-th Bessel function. This is in agreement with theoretical predictions starting from the driven spin-boson model and applying real-time path integral methods. In addition, we report on subharmonic-like resonances in spectroscopy measurements. They are related to excitations in the combined driven flux-qubit-SQUID system and are explained in terms of avoided level crossings in the Floquet spectrum.