Abstract
We experimentally demonstrate strongly enhanced coupling between excited magnons in an Yttrium Iron Garnet (YIG) film and microwave photons in an inverted pattern of split-ring resonator (noted as ISRR). The anti-crossing effects of the ISRR’s photon mode and the YIG’s magnon modes were found from |S21|-versus-frequency measurements for different strengths and directions of externally applied magnetic fields. The spin-number-normalized coupling strength (i.e. single spin-photon coupling) {g}_{{rm{eff}}}/2pi sqrt{N} was determined to 0.194 Hz ({g}_{{rm{eff}}}/2pi = 90 MHz) at 3.7 GHz frequency. Furthermore, we found that additional fine features in the anti-crossing region originate from the excitation of different spin-wave modes (such as the magnetostatic surface and the backward-volume magnetostatic spin-waves) rather than the Kittel-type mode. These spin-wave modes, as coupled with the ISRR mode, modify the anti-crossing effect as well as their coupling strength. An equivalent circuit model very accurately reproduced the observed anti-crossing effect and its coupling strength variation with the magnetic field direction in the planar-geometry ISRR/YIG hybrid system. This work paves the way for the design of new types of high-gain magnon-photon coupling systems in planar geometry.
Highlights
Information exchange with preserved coherence is essential in quantum-information applications
The most recent studies have focused on hybrids composed of Yttrium Iron Garnet (YIG) thin film and the split-ring resonator (SRR) in planar geometry[20,22,23,24], because such hybrid systems offer an advantage with respect to integration with current on-chip devices[25]
To achieve a strong electrodynamic coupling, the ISRR was designed on the ground plane just below the microstrip line, as shown in the inset of Fig. 1a
Summary
Information exchange with preserved coherence is essential in quantum-information applications. In most studies on magnon-photon coupling, three-dimensional (3D) structures consisting of a cavity resonator and an YIG sphere have been used in experiments[3,4,5,6,7,8,9,10] in which the photon and magnon modes were excited by the photon cavity boundary and the spin precession under an external static magnetic field, respectively. The cavities have a quality factor higher than those of the planar (e.g. SRR or inverted-SRR) structures, their inability to excite higher-order spin-wave modes in magnetic systems[26,27] does not sufficiently affect the magnon-photon coupling strength in cavity-based systems. To excite the higher-order spin-wave modes, the cavities need to be specially designed[28], but this always is difficult This disadvantage of the cavity system is not an issue in stripline-planar resonator-based systems. The planar structure and easy localization of microwave fields both allow for much excitation of the higher-order spin-wave modes, which can contribute to photon-magnon coupling[22,24]
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