Slow Light via EIT

Physics: EIT slow light: v_g = c/(1 + ωₚ·Ng²/(γ·Ω_c²)) where N=density, g=coupling, γ=decay, Ω_c=coupling Rabi frequency. Hau et al. 1999: v_g = 17 m/s (c/17,647,058) in BEC of Na atoms. Phillips 2001: stored and retrieved a light pulse after 1 ms in Rb vapor. Fleischhauer-Lukin dark-state polariton: photon coherence maps to spin-wave (atomic coherence) — group velocity = 0 is fully stored state. Bandwidth-delay tradeoff: τ_delay × Δω ∝ optical depth OD. Quantum memory fidelity limited by ground-state decoherence time T₂.