Quantum hybrids: connecting spin excitations to resonators

Hans-Gregor Huebl, Walther-Meißner-Institut

Magnons - the quantized excitations of a magnetic system - are not only pivotal for spintronics applications, but also probe the fundamental properties of magnetic systems. For example, the field of magnetization dynamics deduces from the dynamic response of the spin system the type of magnetic order and relevant magnetic anisotropy parameters. Moreover, this allows to extract the interaction of the magnetization dynamics with other degrees of freedom such as solid-state excitations. Typically, the electromagnetic waves used for this purpose are thought as weakly perturbing stimuli and probes. However, if the interaction between magnetic excitations and the drive becomes strong, collective effects can arise and have the ability to modify or completely alter the character of the magnetization dynamics. One such example is a hybrid system formed by a spin excitation and a resonator.

In my presentation, I will discuss the impact on magnetic excitations due to their coupling to an auxiliary system using the example of spin-excitations in a microwave cavity. In this context, I will introduce characteristic fingerprints, a categorization scheme of the coupling regime, and frequently used figures of merit like the cooperativity or coupling rate.

In addition, the magnetization excitations are naturally linked to a sense of precession via the gyromagnetic ratio. This offers the opportunity to access the angular momentum carried by other excitations, even for an engineered hybrid system. In the second part of my presentation, I will discuss the coupling of magnons to the extrinsic phonons of a bulk acoustic resonator via the magnetoelastic interaction. Here, I will focus on the presently demonstrated coupling regimes, and the ability to use this system as a probe for the angular momentum properties of the phonons.

I will conclude the presentation with an outlook on future opportunities for the field of quantum science and, in particular, for sensing and transduction applications.

Please sign up here in order to get the Zoom link and regular announcements of the upcoming talks.