Operating a passive on-chip superconducting circulator: device control and quasiparticle effects

TL;DR

This paper analyzes the operation and optimization of a passive on-chip superconducting circulator based on Josephson junctions, addressing circuit tuning and quasiparticle effects to enable practical quantum circuit integration.

Contribution

It provides a detailed analysis of device control parameters and quasiparticle effects, offering a pathway for practical implementation of superconducting circulators.

Findings

Optimal parameter constraints for circulation achieved through adiabatic elimination.

Numerical optimization identifies quick convergence to optimal control settings.

Quasiparticle tunneling impacts signal circulation, informing device robustness.

Abstract

Microwave circulators play an important role in quantum technology based on superconducting circuits. The conventional circulator design, which employs ferrite materials, is bulky and involves strong magnetic fields, rendering it unsuitable for integration on superconducting chips. One promising design for an on-chip superconducting circulator is based on a passive Josephson-junction ring. In this paper, we consider two operational issues for such a device: circuit tuning and the effects of quasiparticle tunneling. We compute the scattering matrix using adiabatic elimination and derive the parameter constraints to achieve optimal circulation. We then numerically optimize the circulator performance over the full set of external control parameters, including gate voltages and flux bias, to demonstrate that this multi-dimensional optimization converges quickly to find optimal working points. We also consider the possibility of quasiparticle tunneling in the circulator ring and how it affects signal circulation. Our results form the basis for practical operation of a passive on-chip superconducting circulator made from a ring of Josephson junctions.