Zero-crossing Shapiro step generated in a niobium in-line Josephson gate

We demonstrate a zero-crossing Shapiro step generated in a magnetically-coupled Josephson gate, where a long Josephson junction and a control line are placed in-line. The operation is based on the imbalanced evolution of the junction phases owing to the different amplitudes of the positive and negative critical current. A test circuit was fabricated using a Nb/AlOx/Nb junction technology. When we applied a rf signal of 15.2GHz, we observed a Shapiro step that crossed the zero-current axis at the voltage position of the 1st order. The experimental results were quantitatively reproduced by simulation.