Josephson Metamaterial with a Tunable Kerr Constant

Superconducting circuits rely heavily on the non-linearity inherent in Josephson Junctions. The magnitude of this nonlinearity can be set either at fabrication or tuned with a superconducting quantum interference device (SQUID). Generally, the sign of the Kerr coefficient in the cosine energy phase relation for Josephson junctions cannot be tuned. Here we will present a unit cell design of a metamaterial which allows the Kerr coefficient to be tuned over a wide range in magnitude and can even change sign from positive to negative. Experimental results will be presented showing agreement with theory for the Josephson chain. We will also demonstrate how this metamaterial can be applied to recent efforts in realizing large superinductors and efficient traveling-wave parametric amplifiers (TWPA), two applications which have heavily relied on series arrays of Josephson junctions.