Indirect coupling between two cavity modes via ferromagnetic resonance

Abstract

We experimentally realize indirect coupling between two cavity modes via strong coupling with the ferromagnetic resonance in Yttrium Iron Garnet (YIG). We find that some indirectly coupled modes of our system can have a higher microwave transmission than the individual uncoupled modes. Using a coupled harmonic oscillator model, the influence of the oscillation phase difference between the two cavity modes on the nature of the indirect coupling is revealed. These indirectly coupled microwave modes can be controlled using an external magnetic field or by tuning the cavity height. This work has potential for use in controllable optical devices and information processing technologies.The indirect coupling of cavity modes via a waveguide has been studied theoretically and experimentally for use in optical information processing 1 . This indirect coupling dramatically modifies the transmission spectra, and is widely used for optical filtering, buffering, switching, and sensing in photonic crystal structures 2-5 . For micro/nano disk optical cavities, coupling properties are determined by the spatial distance between the disk and the waveguide during the fabrication process. Therefore, a tunable coupling between indirectly coupled cavity modes is required for potential applications.Recently, strong coupling between a microwave cavity mode and ferromagnetic resonance (FMR) has been realized at room temperature 6-17 . Exchange interactions lock the high density of spins in YIG into a macro-spin state, leading to strong coupling with a cavity mode which can be adjusted using an external magnetic field. Potential applications of this form of strong coupling are currently being explored. For example, indirect coupling between the FMR in two YIG spheres has produced dark magnon modes with potential uses in information storage technologies 18 , and the FMR of YIG has been indirectly coupled with a qubit through a microwave cavity mode 19 . Instead of using a microwave cavity mode to build a bridge between two oscillators, we have used the FMR in YIG to produce indirect coupling between two cavity modes.In this work, we present two cavity modes which indirectly couple via their strong coupling with the FMR in YIG at room temperature. The two cavity modes are labelled h ω1 (ω) and h ω2 (ω) respectively, and are independent of each other when there is no direct coupling between them. Here ω 1 and ω 2 are the uncoupled resonance frequencies of each cavity mode and ω is the input microwave frequency. The two cavity modes can be indirectly coupled with each other when they both individually interact with the FMR in YIG and this indirect coupling can be controlled using an external magnetic field. We found that the microwave transmission properties change dramatically for the coupled modes as the external field is tuned. Our experimental results,

Robust magnon-photon coupling in a planar-geometry hybrid of inverted split-ring resonator and YIG film

“…Table 1 shows those values as obtained from both the planar and the 3D cavity hybrid systems. It is evident that the value of (or k ) obtained from the present study is higher than those obtained from the 3D cavity/YIG sphere hybrids 8 – 13 , 20 , 29 , but is lower than those obtained from some of co-axial- 28 and planar-based hybrid systems 20 , 24 . Recently, the dependence of the coupling strength on the diameter of YIG spheres with a 3D cavity was demonstrated by Tabuchi et al .…”

“…In this ISRR-YIG hybrid, we found strong magnon-photon coupling along with a nearly five times higher gain and a wider frequency band relative to those of the SRR of the same dimensions as the ISRR. The spin-number-normalized coupling strength showed an enhanced value among those reported so far for 3D systems 4 , 8 – 10 , 12 , 29 and SRR-based planar hybrids 20 – 24 . The magnetic-field-direction-dependent photon-magnon coupling is also presented and interpreted using an equivalent circuit model in consideration of spin-wave excitations at specific measurement geometries.…”

“…In order to elucidate the underlying physics of the observed high-gain strong anti-crossing effect from the ISSR-YIG hybrid sample, we considered the degrees of co-operativity of different resonance systems in the field of quantum information. Three different models have been proposed: coupled harmonic oscillators 10 , 20 , 21 , dynamic phase correlation 10 , 29 , and microscopy theory 28 , 33 . Here, we adapted the harmonic oscillator model, as it can quantitatively describe the experimentally observed modes in coupled systems and also can easily be generalized for a multi-mode coupling system.…”

Topological properties of a coupled spin-photon system induced by damping

“…An interesting possibility offered by the spin-photon system is to tune the topology with additional modes, for example using spin waves [36,37], multiple FM materials [12,15], or additional cavity modes [38]. The use of additional cavity modes is particularly intriguing as this can be realized in a height tuneable cavity which offers control over the mode frequencies and cavity damping which is not necessarily available with spin waves.…”

Cavity Spintronics: An Early Review of Recent Progress in the Study of Magnon–Photon Level Repulsion

“…Furthermore, since the hybridization occurs with a cavity photon, the wave vector is fixed and therefore the most relevant feature to consider is the field dependence of the FMR, which is accounted for by allowing ω r to vary. Actually, even in situations where the photon wave vector is controlled through tuning the cavity height, the relevant physical influence is to tune ω c and therefore the length scales between the photon and magnon wavelengths do not influence the observed behaviour [57]. Polarization effects of the photons have also not been accounted for in this approach.…”