Wang, C., Li, A., Lu, Y., Kanungo, S. K., Yoshida, S., Dunning, F. B., & Killian, T. C. (2026). Nonlocal spatial correlations in an interacting atomic gas. Physical Review A, 113(2), Article 022803. https://doi.org/10.1103/2q22-grqy
We report in situ measurements of the nonlocal two-body spatial correlation function 𝑔⁽²⁾(𝑅) in an ultracold Bose gas with strong interactions using photoassociation of ultra-long-range Rydberg molecules (ULRRMs) as a spatially selective probe. This technique provides access to 𝑔⁽²⁾(𝑅) on length scales from 60 to 180 nm, bridging the gap between short-range and long-range correlation measurements. The large 𝑠-wave scattering length of ⁸⁶Sr (𝑎=811𝑎₀) enables exploration of the universal regime where 𝑔⁽²⁾(𝑅) is governed solely by two-body interactions. Comparison with a weakly interacting isotope, 84 Sr, highlights interaction-induced suppression of pair correlations. The measured correlation functions agree quantitatively with ab initio calculations based on the two-body reduced density matrix, without adjustable parameters. Our results establish Rydberg molecular photoassociation as a powerful tool for probing nonlocal correlations in situ in strongly interacting quantum gases.
