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The Tavis-Cummings model extends the Jaynes-Cummings model to several two-level systems exchanging excitations with a common quantized normal mode under the rotating-wave approximation. It conserves total excitation number. Equal coupling preserves permutation-symmetric atomic sectors, allowing finite-dimensional reductions for a fixed initial excitation number.

A mobile spin-triplet excitation above a singlet background in a quantum magnet. At low density, an appropriate triplet branch can be described as bosonic quasiparticles with an effective mass and repulsive interaction. Applied magnetic field can lower one branch toward condensation. The term does not imply that the total excitation number is conserved on thermodynamic timescales.