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//! Cavity Magnonics - Hybrid Quantum Systems
//!
//! Cavity magnonics studies the coupling between magnons (spin wave quanta)
//! and photons (electromagnetic wave quanta) in microwave cavities. When the
//! coupling strength exceeds the dissipation rates, the system enters the
//! **strong coupling regime**, forming hybrid magnon-polariton states.
//!
//! ## Physical Principle
//!
//! A ferromagnetic sphere (typically YIG) placed in a microwave cavity
//! experiences:
//!
//! 1. **Ferromagnetic Resonance (FMR)**: Uniform precession mode (Kittel mode)
//! - Frequency: ω_FMR = γ H_bias
//! - Linewidth: Δω_m ≈ α ω_FMR (ultra-narrow for YIG: ~1 MHz)
//!
//! 2. **Cavity Photon Mode**: Standing electromagnetic wave
//! - Frequency: ω_cavity ≈ 2-20 GHz (X-band, K-band)
//! - Linewidth: κ ≈ 1-10 MHz
//!
//! 3. **Magnetic Dipole Coupling**: g ≈ 10-100 MHz
//! - Interaction: oscillating cavity magnetic field ↔ precessing magnetization
//!
//! ## Strong Coupling Regime
//!
//! When cooperativity C = 4g²/(κγ_m) >> 1:
//!
//! - **Level anticrossing**: Avoided crossing in transmission spectrum
//! - **Vacuum Rabi splitting**: Δω = 2g
//! - **Coherent energy exchange**: Photon ↔ Magnon conversion
//!
//! ## Applications
//!
//! ### 1. Quantum Information Processing
//! - Magnons as quantum memory (long coherence time)
//! - Photons for information transfer
//! - Hybrid quantum transducers
//!
//! ### 2. Magnon Amplification
//! - Stimulated emission of magnons
//! - Magnon laser (analogous to photon laser)
//!
//! ### 3. Non-reciprocal Devices
//! - Isolators and circulators
//! - One-way information transfer
//!
//! ## Key Experiments
//!
//! - H. Huebl et al., "High Cooperativity in Coupled Microwave Resonator
//! Ferrimagnetic Insulator Hybrids", Phys. Rev. Lett. 111, 127003 (2013)
//! - Y. Tabuchi et al., "Coherent coupling between a ferromagnetic magnon
//! and a superconducting qubit", Science 349, 405 (2015)
//!
//! ## References
//!
//! Based on research by:
//! - Prof. Y. Nakamura (RIKEN/UTokyo) - Quantum magnonics
//! - Prof. G. E. W. Bauer (Tohoku Univ) - Magnon spintronics
//! - Prof. Y. Otani (RIKEN) - Spin-wave devices
pub use HybridSystem;