Measurement of a Magnonic Crystal at Millikelvin Temperatures

TL;DR

This paper demonstrates the first measurement of a magnonic crystal at millikelvin temperatures, revealing a magnonic bandgap but also highlighting challenges like increased damping that need addressing for quantum applications.

Contribution

It provides the first experimental evidence of magnonic crystal behavior at millikelvin temperatures, essential for quantum information processing.

Findings

Magnonic bandgap observed at 20 mK.

Spin-wave damping higher than expected at low temperatures.

Feasibility of using MCs in quantum experiments demonstrated.

Abstract

Hybrid systems combining magnons and superconducting quantum circuits have attracted increasing interest in recent years. Magnonic crystals (MCs) are one of the building blocks of room-temperature magnonics and can be used to create devices with an engineered band structure. These devices, exhibiting tunable frequency selectivity and the ability to store travelling excitations in the microwave regime, may form the basis of a set of new tools to be used in the context of quantum information processing. In order to ascertain the feasibility of such plans, MCs must be demonstrated to work at the low temperatures required for microwave-frequency quantum experiments. We report the first measurements of the transmission of microwave signals through an MC at 20 mK and observe a magnonic bandgap in both continuous-wave and pulsed excitation experiments. The spin-wave damping at low temperatures in our yttrium iron garnet MC is higher than expected, indicating that further work is necessary before the full potential of quantum experiments using magnonic crystals can be realised.