Regensburg 2007 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 7: Quantum Coherence and Quantum Information Systems II
TT 7.4: Talk
Monday, March 26, 2007, 14:45–15:00, H20
Observation of Macroscopic Quantum Behavior in π Josephson Junctions with Ferromagnetic Interlayer — •Karl Madek1, Martin Weides2, Sven Beutner1, Achim Marx1, Hermann Kohlstedt2, and Rudolf Gross1 — 1Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, D-85748 Garching — 2Institut für Festkörperforschung und CNI, Forschungszentrum Jülich, D-52425 Jülich
Superconducting circuits are particularly interesting for the implementation of quantum information systems. For the realization of superconducting flux qubits the use of π-Josephson junctions is promising, since it would allow the design of qubits in a quiet configuration. Such π-junctions have been successfully realized using Josephson junctions with an additional thin ferromagnetic interlayer. However, nothing is known so far on the quantum behavior of these junctions.
We performed measurements of both the macroscopic quantum tunneling of the phase variable and the level quantization in Nb/AlOx/CuNi/Nb π-Josephson junctions. Escape rate measurements show a crossover from the thermally activated regime, in which the phase variable escapes by thermal activation from a local minimum of the potential well, to the quantum regime, where macroscopic quantum tunneling dominates. Microwave spectroscopy experiments give direct evidence for energy level quantization. Both quantized energy levels in the tilt washboard potential as well as multi-photon transitions between the levels have been observed.
This work was supported by the DFG through SFB 631.