Regensburg 2004 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 17: Postersitzung II: Transport, Quantenkoh
ärenz, Quantenflüssigkeiten

TT 17.25: Poster

Dienstag, 9. März 2004, 14:30–19:00, Poster A

Microwave spectroscopy of long Josephson junctions in the quantum regime — •A. Kemp¹, A. Lukashenko¹, Y. Koval¹, J. Lisenfeld¹, M.V. Fistul¹, A. Wallraff², and A.V. Ustinov¹ — ¹Physikalisches Institut III, Universität Erlangen-Nürnberg, 91058 Erlangen, Germany — ²Dept. Applied Physics, Yale University, New Haven, CT 06520, USA

We experimentally investigate the quantum escape of the phase in flux-free narrow annular Josephson junctions under influence of microwaves. A measurement technique developed earlier [1] based on ramp-type measurements enables us to resolve the populations of the ground state and the first excited state. We probe the level structure of the junction with small magnetic fields applied and at currents close to the fluctuation-free critical current. The data obtained are compared to the theory [2] describing the escape as dissociation of a vortex-antivortex pair and predicting the specific scaling of the energy level spacing with the bias current. A rather good agreement is found, while the detailed behavior of the observed resonances leaves few open questions.

[1] A. Wallraff et al., Rev. Sci. Inst. 74, 3740 (2003)

[2] M.V. Fistul et al., to appear in Phys.Rev.Lett. (cond-mat/0307705)