Passive superconducting circulator on a chip

TL;DR

This paper demonstrates the first passive on-chip superconducting circulator using a Josephson loop, enabling nonreciprocal microwave signal routing compatible with superconducting quantum circuits.

Contribution

It introduces a novel passive superconducting circulator made from a Josephson loop, tunable with DC fields, avoiding external drives or magnetic fields that impair superconductivity.

Findings

Evidence of nonreciprocal scattering consistent with theoretical models

Excellent agreement between experimental results and simulations

Analysis of quasiparticle tunneling using a hidden Markov model

Abstract

An on-chip microwave circulator that is compatible with superconducting devices is a key element for scale-up of superconducting circuits. Previous approaches to integrating circulators on chip involve either external driving that requires extra microwave lines or a strong magnetic field that would compromise superconductivity. Here we report the first proof-of-principle realisation of a passive on-chip circulator which is made from a superconducting loop interrupted by three notionally-identical Josephson junctions and is tuned with only DC control fields. Our experimental results shows evidence for nonreciprocal scattering, and excellent agreement with theoretical simulations. We also present a detailed analysis of quasiparticle tunneling in our device using a hidden Markov model. By reducing the junction asymmetry and utilising the known methods of protection from quasiparticles, we anticipate that Josephson-loop circulator will become ubiquitous in superconducting circuits.