Josephson Metamaterial with a Widely Tunable Positive or Negative Kerr Constant

The optical Kerr effect, in which a medium's refractive index is affected by the intensity of the transmitted light, is exploited not only in conventional optics, but also in superconducting circuits. This article reports a Josephson-junction-based metamaterial with a widely tunable Kerr constant that can even change sign. Controlled by an external magnetic field, this material can speed up or slow down the phase velocity of light per the intensity of the propagating electromagnetic wave. Such an engineered medium could be used for phase matching in traveling-wave parametric amplifiers, or in superconducting hardware for encoding or reading out quantum information.