On-Chip Superconducting Microwave Circulator from Synthetic Rotation

We analyze a design for a microwave circulator which could replace many of the commercial ferrite circulators that are ubiquitous in contemporary quantum superconducting microwave experiments. The lossless, lumped-element design is capable of being integrated on chip with other superconducting microwave devices, thus circumventing the many performance-limiting aspects of ferrite circulators. The design is based on the dynamic modulation of dc superconducting microwave quantum interference devices that function as nearly linear, tunable inductors. The connection to familiar ferrite-based circulators is a simple frame boost in the internal dynamics' equation of motion. In addition to the general, schematic analysis, we also give an overview of many considerations necessary to achieve a practical design with a tunable center frequency in the 4-8-GHz frequency band, a bandwidth of 240 MHz, reflections at the -20-dB level, and a maximum signal power of approximately 100 microwave photons per inverse bandwidth.