Collective-Mode and Hydrodynamic Constraints on Magnon-Based Quantum Memory

  This paper analyzes fundamental physical constraints on magnon-based quantum 

  memory systems. We examine collective-mode behavior and magnetohydrodynamic   

  (MHD) limits that govern the scalability of photon-magnon quantum state       

  transfer.                                                                     

  Key findings:                                                                 

  - Spin wave propagation limits spatial addressing resolution                  

  - Magnetic Reynolds number R_m ≈ 10⁻¹² confirms diffusion-dominated regime    

  - Maximum achievable channels: N_max ~ 10³-10⁴ via frequency-based addressing

  - Channel crosstalk analysis provides design guidelines                       

  This work complements the theoretical framework (Paper I) and experimental    

  proposal (Paper II) in a three-paper series on magnetic quantum memory.       

  Keywords: quantum memory, magnons, spin waves, magnetohydrodynamics,          

  photon-magnon coupling