Magneto-Optical Trap
3D trapping · Zeeman shift · σ+/σ⁻ beams
Physics: MOT: 6 counter-propagating σ+/σ⁻ beam pairs + quadrupole magnetic field. Zeeman effect: B-field shifts magnetic sublevels ΔE = g_F μ_B m_F B. Displaced atoms preferentially absorb photons pushing them back to center. Restoring force κ ∝ b·Γ (b = field gradient); damping ∝ δ·Γ. Typical: 10⁸–10¹⁰ atoms trapped at ~100 μK. Loading from Zeeman slower. Gray molasses (D1 line) reaches μK. First MOT: Raab et al. 1987. Nobel Physics 1997 (Chu, Cohen-Tannoudji, Phillips). Precursor to BEC via evaporative cooling in magnetic trap or crossed optical dipole trap.