Resonant light scattering by a slab of ultracold atoms

A gas of ultracold atoms probed with laser light is a nearly-ideal experimental realization of a medium of resonant point-like scatterers, a key problem from condensed matter to biology or photonics. Yet, several recent experiments have reported large discrepancies with theory. In this work, we measure the complex transmission through a slab of ultracold two-level atoms with an interferometric technique. We find good agreement with first-principles simulations of mutually-coupled, laser-driven dipoles, and provide an explanation for the discrepancies in earlier measurements.

💡 Research Summary

In this work the authors investigate resonant light scattering from a quasi‑two‑dimensional slab of ultracold 174Yb atoms, a system that closely approximates an ensemble of point‑like resonant scatterers. They prepare a single‑site optical lattice containing up to 4.5 × 10⁴ atoms, yielding a Gaussian thickness Δz≈1.9 k₀⁻¹ and surface densities eρ₂D ranging from 0.13 to 0.42. The atoms are driven on the ¹S₀ → ¹P₁ transition (λ≈399 nm) with a weak σ⁺‑polarized probe (I≈0.2 I_sat) for 5 µs to suppress motion.

The key experimental innovation is a Mach‑Zehnder‑type interferometric measurement that simultaneously yields the intensity transmission T and the phase shift Δφ imprinted on the probe. Two mutually coherent beams (probe and reference) overlap on a high‑resolution camera at a small angle, producing interference fringes. By fitting each fringe to S(x)=A