Subterranean power lines in high-density integrated Josephson circuits

We found from simulations that wide power lines are required to make bias currents of Josephson gates uniform. Magnetic noise due to large power current decreases the critical current of the adjacent gate. To enhance circuit integration and to stabilize circuit operation, we proposed a power line laid under the ground plane. The gates can be located above the power line inserting the ground plane. The new power line can make whole chip areas active for gates however wide the line is. We confirmed that the ground plane shields the gates from magnetic noise. We fabricated some test circuits using the new power lines and confirmed their operations.<>