Widely tunable on-chip microwave circulator for superconducting quantum circuits

TL;DR

This paper presents a novel on-chip microwave circulator with GHz tunability, enabling non-reciprocal signal routing in superconducting circuits without magnets or bias tones, featuring high isolation, low loss, and reconfigurability.

Contribution

It introduces a widely tunable, magnet-free microwave circulator compatible with superconducting circuits, with dynamic reconfigurability and high performance over GHz frequencies.

Findings

Isolation exceeds 20 dB over tens of MHz bandwidth

Insertion loss as low as 0.9 dB at certain frequencies

Operates linearly up to hundreds of fW signal power

Abstract

We report on the design and performance of an on-chip microwave circulator with a widely (GHz) tunable operation frequency. Non-reciprocity is created with a combination of frequency conversion and delay, and requires neither permanent magnets nor microwave bias tones, allowing on-chip integration with other superconducting circuits without the need for high-bandwidth control lines. Isolation in the device exceeds 20 dB over a bandwidth of tens of MHz, and its insertion loss is small, reaching as low as 0.9 dB at select operation frequencies. Furthermore, the device is linear with respect to input power for signal powers up to hundreds of fW ($\approx 10^3$ circulating photons), and the direction of circulation can be dynamically reconfigured. We demonstrate its operation at a selection of frequencies between 4 and 6 GHz.