Josephson junction chain : interplay between Kerr effects and remote ground plane potentials in regime of weak nonlinearity

Orateur : Y. KRUPKO (Néel)

We studied the dispersion and Kerr frequency shifts of plasma modes in one-dimensional Josephson j unction chain in regime of weak nonlinearity. Two samples with different coupling to a transmission line were used : one chain have been imbedded into the microwave strip line, while another have been coupled capacitively to it. The latter configuration enables to learn about internal quality factor of the chain while the first one is more suited to study quantitatively the Kerr effects occurring between different modes in the chain. Experimentally determined low-power dispersion fits excellent the theoretical model if it takes into account the Kerr renormalisation of the bear frequencies and screened Coulomb interactions between metallic islands of the chain that suppress the direct screening to the sample ground. We measured the Self- and Cross-Kerr frequency down-shifts for the lowest 8 modes and deduce from this results the experimental matrix of Kerr coefficients, which we compare to theoretically calculated.

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