Nonreciprocity in Active Josephson Junction Circuits.

摘要

This thesis work explores different ideas for realizing nonreciprocal photon dynamics using active parametric circuits based on Josephson junctions. The motivation stems from developing non-magnetic alternatives to existing nonreciprocal devices, invariably employing magnetic materials and fields and hence limited in their application potential for use with on-chip microwave superconducting circuits. The main idea rests on the fact the "pump" wave (or the carrier) in an active nonlinear system changes the phase of a small modulation signal just as the magnetic field rotates the polarization of the wave propagating in a Faraday medium. All the implementations discussed in this thesis draw from the basic idea of chaining together discrete parametric processes with an optimal phase difference between the respective pumps to realize nonreciprocity. Though discussed specifically for microwave applications using Josephson junctions as a platform, the ideas presented here are generic enough to be adopted for any nonlinear system implementing frequency mixing.