Coherent control of magnon radiative damping with local photon states

Abstract

The collective excitation of ordered spins, known as spin waves or magnons, can in principle radiate by emitting travelling photons to an open system when decaying to the ground state. However, in contrast to the electric dipoles, magnetic dipoles contributed by magnons are more isolated from electromagnetic environment with negligible radiation in the vacuum, limiting their application in coherent communication by photons. Recently, strong interaction between cavity standing-wave photons and magnons has been reported, indicating the possible manipulation of magnon radiation via tailoring photon states. Here, with loading an yttrium iron garnet sphere in a one-dimensional circular waveguide cavity in the presence of both travelling and standing photon modes, we demonstrate an efficient photon emissions from magnon and a significant magnon radiative damping with radiation rate found to be proportional to the local density of states (LDOS) of photon. By modulating the LDOS including its magnitude and/or polarization, we can flexibly tune the photon emission and magnon radiative damping on demand. Our findings provide a general way in manipulating photon emission from magnon radiation for harnessing energy and angular momentum generation, transfer and storage modulated by magnon in the cavity and waveguide electrodynamics. arXiv:1902.06795v2 [cond-mat.mes-hall]

Dissipative couplings in cavity magnonics

“…In Refs. [48][49][50][51]54,56,57 the dissipative coupling was due to dissipation processes, while in Ref. 61,62 the level attraction was caused by the interference effect between two driven tones.…”

“…Among them, the 1D waveguide-cavity setup 48,56,57 can adjust the weights of the traveling wave and standing waves by tuning the global geometry via rotating the relative angle θ between the two waveguide transitions. To capture such a wave controllability, Yao et al 56,57 developed a theory for calculating the photon density of state, by considering all the photon modes and carefully distinguishing the standing and traveling wave parts. This theoretical picture provides a good understanding of the difference between the effect of traveling and standing waves on light-matter interaction.…”

“…Yao et al 56,57 show that quantitatively, the amount of the radiative linewidth changing of the magnon-like hybridized mode can be mapped to the density of photon states. It provides another way for verifying the influence of the traveling wave on the effect of magnon-photon coupling.…”

The microscopic origin of magnon-photon level attraction by traveling waves: Theory and experiment

“…Thus, it allows us to obtain information aboutg s andg b by characterizing the magnon radiative linewidth broadening. Specifically, when away from the resonance ω c ,g s tends to be zero and πg 2 b is the broadening of the magnon mode due to the radiation [29], through which we can experimentally measure the coupling strengthg b . This broadening becomes π (g s +g b ) 2 at the resonance, through which we can determineg s as well.…”

“…We note that the systems used in the experiments [22,26,27] are often open and coupled to the environment, allowing the magnon to radiate out energy by emitting a traveling photon when the magnon mode is detuned from the cavity resonance. Thus, these systems are dissipative in nature [29]. The existence of traveling modes and their effect on magnon-photon hybridization have not been sufficiently explored to understand the phenomenon of the level attraction.…”