HTS Josephson heterodyne oscillator on a pulse-tube cryocooler

A high-temperature superconducting (HTS) Josephson heterodyne oscillator based on step-edge junction technology has recently been developed (Du et al 2008 Appl. Phys. Lett. 93 033507, Macfarlane et al 2009 IEEE Trans. Appl. Supercond. 19 920). In this work, the implementation and characterization of such a heterodyne oscillator on a compact pulse-tube cryocooler (PTC) are presented. The rf performance of the oscillator cooled by the cryocooler is compared to that of the same device when cooled in the quiet gas phase of a liquid helium Dewar. Any measurable influence of additional electromagnetic noise and mechanical vibration of the cryocooler on the oscillator performance is assessed by measuring the linewidth broadening of the heterodyne oscillation. The cryocooled oscillator demonstrated excellent performance and negligible excess noise was observed when operating the PTC.