$\mathcal{PT}$-symmetric cavity magnomechanics with gain-assisted transparency and amplification

TL;DR

The paper develops a theoretical framework for a PT-symmetric cavity magnomechanical system in which a traveling-field drive introduces non-Hermitian gain. By coupling a microwave cavity mode to a YIG-m magnon mode and a magnomechanical phonon mode, the authors show that MMIT can be tuned from a single to a double window in the Hermitian limit, and further transformed into gain-assisted, asymmetric MMIT near exceptional points when the non-Hermitian coupling is present. They demonstrate that finite magnomechanical coupling reshapes MMIT into Fano-like resonances and that the probe phase exhibits strongly non-Lorentzian dispersion, enabling highly tunable slow- and fast-light behavior. The work highlights the potential of engineered PT-symmetry in cavity magnomechanics for reconfigurable quantum transduction, amplification, and precision sensing near exceptional points.

Abstract

We investigate magnomechanically induced transparency in a parity-time-symmetric cavity magnomechanical system with traveling-field-induced non-Hermiticity. The setup consists of a microwave cavity mode coupled to magnons in a single-crystal yttrium iron garnet sphere, which in turn are hybridized with a vibrational mechanical mode through magnetostrictive interaction. In the Hermitian regime, strong photon-magnon coupling generates a single transparency window in the cavity transmission, which splits into a doublet when the magnon is coherently hybridized with the mechanical mode via magnomechanical coupling. This establishes a versatile platform in which the transparency spectrum can be engineered from single- to multi-window response using experimentally accessible, scaled magnomechanical interactions. When a non-Hermitian coupling is introduced, the system enters a parity-time-broken regime in which the transparency ceases to be purely passive and becomes gain assisted, leading to asymmetric transmission with amplification on one side of the resonance and enhanced absorption on the other. By tuning the cavity detuning, we convert magnomechanical transparency into Fano-type line shapes with strongly non-Lorentzian phase dispersion and map their deformation into asymmetric, gain-assisted Fano ridges in the joint space of probe and magnon detunings. Finally, we analyze the associated group delay and show that both slow- and fast-light behavior can be widely tuned by varying the photon-magnon and magnomechanical couplings together with the non-Hermitian strength, highlighting parity-time-symmetric cavity magnomechanics as a promising platform for reconfigurable quantum signal processing and enhanced sensing.

Figures (8)

• Figure 1: The schematic description of a diagram of the non-hermitian cavity magnomechanical system centered around a YIG sphere placed in a microwave cavity near the maximum magnetic field $\zeta$ for the cavity mode and simultaneously in a uniform bias magnetic field establishing the magnon photon phonon coupling and The cavity system is probed through a probe input on one side $\eta_{p}$ with a traveling field at angle $\theta$ along $x$-axis and $y$-axis, respectively.
• Figure 2: (Color online) Normalized cavity probe transmission $T(\Delta_{p})$ and phase $\phi(\Delta_{p})$ in the Hermitian regime ($\Gamma=0$). (a),(b) Single-window MMIT for $G_{b}/\Delta_{m}=0$ and increasing photon--magnon coupling $G_{a}/\Delta_{a}$ (values indicated). (c),(d) Double-window MMIT for finite magnomechanical coupling $G_{b}/\Delta_{m}\neq 0$, with $G_{a}/\Delta_{a}$ unchanged. Introducing $G_{b}$ splits the single transparency resonance into two magnomechanical transparency windows and gives rise to two corresponding steep dispersive features in the phase. The other numerical parameters that we consider in our calculations are $\kappa_a/\Delta_a=0.08,\kappa_m/\Delta_m=0.08$
• Figure 3: (Color online) Normalized cavity probe (a) transmission $T(\Delta_{p})$ and (b) phase $\phi(\Delta_{p})$ as functions of the normalized probe detuning $\Delta_{p}/\omega_{b}$ for nonzero non-Hermitian coupling $\Gamma$, with $G_{a}/\Delta_{a}=2$ and $G_{b}/\Delta_{m}=0.1$. The presence of $\Gamma\neq 0$ converts the Hermitian MMIT window into a gain-assisted transparency feature with $T(\Delta_{p})>1$ and a strongly asymmetric line shape: transmission is suppressed on the loss-dominated (negative-detuning) side and amplified on the gain-dominated (positive-detuning) side, accompanied by a sharply varying phase dispersion near the amplified resonance. The remaining parameters are the same as in Fig. \ref{['Fig2']}.
• Figure 4: (Color online) Cavity probe transmission $T(\Delta_{p})$ and phase $\phi(\Delta_{p})$ as functions of the probe detuning $\Delta_{p}$ for fixed non-Hermitian parameter $\Gamma/\omega_{b}=2$ and photon--magnon coupling $G_{a}/\Delta_{a}=2$, and for different magnomechanical couplings $G_{b}/\Delta_{m}$ (as indicated in the legend). Increasing $G_{b}/\Delta_{m}$ enhances the magnomechanical backaction on the non-Hermitian hybrid modes, leading to a pronounced reshaping of the gain-assisted MMIT profile and a steeper, more asymmetric phase dispersion near the amplified transparency region. The remaining parameters are the same as in Fig. \ref{['Fig2']}.
• Figure 5: (Color online) (a) Cavity probe transmission $T(\Delta_{p})$ and (b) phase response $\phi(\Delta_{p})$ for different cavity detunings $\Delta_{a}/\kappa_{a}$ (values indicated in the legend), at fixed non-Hermitian coupling $\Gamma/\kappa_{a}=2$, photon--magnon coupling $G_{a}/\kappa_{a}=2$, and magnomechanical coupling $G_{b}/\kappa_{a}=0.1$. Varying $\Delta_{a}/\kappa_{a}$ transforms the MMIT-like feature into asymmetric Fano profiles and produces strongly non-Lorentzian phase dispersion, with amplification on one side of the resonance and enhanced absorption on the other. The remaining parameters are the same as in Fig. \ref{['Fig2']}.