Single-mode magnon-polariton lasing and amplification controlled by dissipative coupling

Abstract

We demonstrate single-mode lasing of magnon polaritons in a cavity magnonic system enabled by dissipative coupling between two passive modes, microwave cavity mode and magnon mode in a ferrimagnetic spin ensemble. The cavity mode is partially compensated through a feedback circuit, which reduces its linewidth but retains its dissipative nature. By tuning the compensation strength and dissipative coupling strength, we reach a system cooperativity of unity, marking the lasing threshold and the formation of a zero-linewidth polariton mode. This mode also corresponds to a perfect Friedrich-Wintgen bound state in the continuum. Further increase of the cooperativity drives the system into the strong dissipative coupling regime, where magnon polariton amplification arises between two real frequency scattering poles. These results reveal that dissipative coupling cooperativity carries a clear physical meaning and serves as a key parameter for controlling phase transitions. Dissipative coupling offers an alternative paradigm for tailoring light matter interactions, paving the way for advances in both information processing and quantum technologies.

Figures (4)

• Figure 1: (a),(b) Schematic diagrams of the coherently (a) and dissipatively (b) coupled cavity magnonic systems. (c) Diagram of the dissipative coupling regimes. The white line corresponds to the unity cooperativity, which divides the areas into passive (blue) and active (red) regimes. The points A, B, C represent three typical conditions studied in experiments. (d),(e) Evolution of eigenfrequencies in the complex plane for the coherent coupling system (d) and dissipative coupling system (e) as the decay rate $\gamma_{\rm{c}}$ is varied. (f) Imaginary part of $\omega_{+}$ versus cavity photon-magnon detuning $\Delta_{\rm{m}}$ in different coupling regimes. The cyan, blue, and red curves correspond to points A, B and C in (c), respectively.
• Figure 2: (a) Schematic of the experimental device, where the split-ring cavity (blue) is compensated by an active circuit (red) and side-coupled with the waveguide (yellow). The YIG sphere (black) is moved along the waveguide. (b) Measured device transmission versus bias voltage $V$ without the YIG sphere . (c) The compensation rate $G$ fitted from the transmission mapping shown in (b). (d) Typical transmission spectra extracted from (b). The green, blue, gray, yellow, and red curves correspond to $G = 0$, $\beta_{\rm{c}}$, $\kappa_{\rm{c}}/2 + \beta_{\rm{c}}$, $2\kappa_{\rm{c}}/3 + \beta_{\rm{c}}$, and $\kappa_{\rm{c}} + \beta_{\rm{c}}$, respectively. (e) Measured transmission of the dissipatively coupled cavity magnonic system as a function of the bias magnetic field without compensation ($G = 0$). The white dashed lines denote the uncoupled cavity and magnon modes.
• Figure 3: (a)-(c) Calculated $\rm{Im}(\omega_{+})$ versus mode detuning $\Delta_{\rm{m}}$ for different compensation rates $G$. The blue (pink) segment indicates the $\rm{Im}(\omega_{+})$ greater (less) than zero. The green dots represent the real-valued poles (lasing threshold $\rm{Im}(\omega_{+})=0$). The parameters used in these calculations match the experimental results shown in (e) to (g). (e)-(g) Experimentally measured transmission spectra plotted as 3D diagrams versus mode detuning $\Delta_{\rm{m}}$ and cavity field detuning $\Delta_{\rm{c}}$. (d),(h) Spectra extracted from (f) at the positions marked by the arrows in (b). The black, blue, and ultrasharp green curves in (d) correspond to conditions far below, near, and precisely at the lasing threshold, respectively. The chaotic lineshape (pink) in (h) corresponds to the magnon-polariton amplification and instability.
• Figure 4: Threshold of compensation rate and bias voltage for generating magnon-polariton lasing at different dissipative coupling strengths $\Gamma$. The star indicates the cavity compensated to lasing without coupling to the magnon mode. The solid curve is the theoretical fit. The insets show the variation of $\kappa_{\rm{m}}$ as a function of the distance $d$ between the YIG sphere and the waveguide plane.