Reflectionless filter for superconducting quantum circuits Reflectionless filter for superconducting quantum circuits*

Microwave circulators and Josephson Junction parametric amplifiers are critical parts of superconducting quantum measurement systems. In particular JTWPA amplifiers have demonstrated extremely wide band capability, however due to conditional stability (Rollet K factor <1) their performance is degraded by the poor out of band return loss of typical microwave circulators. Protecting super conducting quantum circuits from the non-ideal circulator behavior can be accomplished with a special class of microwave filters known as reflection-less filters. A monolithic Al on Si superconducting reflection-less band pass will be presented that achieves both extremely low insertion over a 50\% fractional bandwidth and return loss below -15dB from DC to above 10GHZ. The python-based design methodology and FEA based optimization of the filter will be presented. Estimation of thermalization along with the theory of the filter's deviation from ideal behavior due to finite delay will be discussed. The talk will conclude with how to use the filter to improve performance of quantum systems that use circulators including improving reduction of high frequency thermal photons and traveling wave parametric amplifier ripple reduction and bandwidth doubling.