Obstacles to Two-Line Josephson Traveling Wave Parametric Amplifier

Obstacles to the two-line Josephson traveling wave parametric amplifier (JTWPA) designs, aimed at increasing the allowed pump wave energy and, hence, the gain growth through the combination of linear and nonlinear lines as pump and signal lines is discussed. This analysis takes into account both the mutual coupling and the discreteness of the artificial waveguide lines. Significant restrictions arise from the cyclical transfer of the traveling wave's energy from one line to the other one with phase step by pi every beat cycle. Moreover, the other restrictions result from the phase mismatch between the pump, signal, and idler waves due to both the coupling and the discreteness of the artificial lines.