Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 31: SC: Tunnelling, Josephson Junctions

TT 31.5: Talk

Thursday, March 25, 2010, 10:30–10:45, H21

Macroscopic quantum properties of Josephson junctions with ferromagnetic interlayer — •Georg Wild^1,2, Christian Probst¹, Achim Marx¹, and Rudolf Gross^1,2 — ¹Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching — ²Physik-Department, Technische Universität München, Garching

Josephson junctions with ferromagnetic interlayer have attracted much interest due to their potential application as π-phase shift elements in flux qubits. However, up to now it is not clear whether magnetic excitations in the ferromagnetic interlayer induce noise and thus prevent the application of these junctions in quantum circuits. To elucidate this question we have fabricated π-coupled Nb/AlO_x/NiPd/Nb superconductor/insulator/ferromagnet/superconductor Josephson junctions and investigated the escape rate out of the zero voltage state into the voltage state. At high temperatures this escape is dominated by thermal activation, while below the crossover temperature T^⋆ it is due to quantum tunneling. In this work we compare the experimentally determined crossover temperature T_exp^⋆ to the theoretically expected value T_th^⋆ to clarify the question whether low-lying excitations in the junction influence its quantum properties. We analyze the only free parameter, the plasma frequency ω_p, by means of Fiske resonance studies and via microwave spectroscopy experiments at mK temperatures.

This work was supported by the DFG via SFB 631 and the Excellence Cluster NIM.