Microwave circulator

A microwave circulator including an integrated circuit having a number of ports and a respective ring segment coupled to each port to allow microwave frequency signals to be transferred between the port and the respective ring segment. The circulator includes multiple respective ring segments arranged to define multiple parallel circulator rings and at least one superconducting tunnel junction interconnecting each pair of adjacent ring segments and/or a plurality of superconducting tunnel junctions interconnecting each pair of adjacent ring segments to form a circulator ring. The ring segments are configured so that when a bias is applied to the tunnel junctions, signals undergo a phase shift as they traverse the tunnel junctions between ring segments, thereby propagating signals to an adjacent port in a propagation direction.