Breaking time-reversal symmetry with a superconducting flux capacitor

TL;DR

This paper introduces a passive on-chip microwave circulator using superconducting tunnel junctions, leveraging symmetry breaking via a bias to achieve high isolation and wide bandwidth without external microwave bias.

Contribution

It proposes a novel superconducting flux capacitor design with two physical implementations, demonstrating high isolation and broad bandwidth in microwave circulation.

Findings

High isolation achieved despite fabrication imperfections

Bandwidth exceeds 500 MHz with realistic parameters

Effective magnetic field enables symmetry breaking without microwave bias

Abstract

We present the design of a passive, on-chip microwave circulator based on a ring of superconducting tunnel junctions. We investigate two distinct physical realisations, based on either Josephson junctions (JJ) or quantum phase slip elements (QPS), with microwave ports coupled either capacitively (JJ) or inductively (QPS) to the ring structure. A constant bias applied to the center of the ring provides the symmetry breaking (effective) magnetic field, and no microwave or rf bias is required. We find that this design offers high isolation even when taking into account fabrication imperfections and environmentally induced bias perturbations and find a bandwidth in excess of 500 MHz for realistic device parameters.