Millimeter wave behavior of superconducting point contact SQUID

A superconducting point contact waveguide SQUID has been operated at 89 GHz. The performance is qualitatively the same as at lower frequencies in agreement with the SQUID model. With the Nb point located across a 0.15 mm high E band waveguide, reflection coefficient measurements were made as a function of both supercurrent phase as controlled by an externally applied magnetic field and millimeter wave power. Large parametric reactance variations were produced by changing the supercurrent phase. As the millimeter wave power is increased flux cycling was observed which involved up to four steps. This behavior corresponds to a flux transition time less than one trillionth of a second. Implications of the cos-phi term and negative resistance effects in the observed behavior of the reflection coefficient are discussed.