Suppression and enhancement of bosonic stimulation by atomic interactions

Abstract The tendency of identical bosons to bunch, seen in the Hanbury Brown–Twiss effect and Bose–Einstein condensation, is a hallmark of quantum statistics. This bunching can enhance the rates of fundamental processes such as atom–atom and atom–light scattering when atoms scatter into already occupied states. For non-interacting bosons, the enhancement of light scattering follows directly from the occupation of the atom’s final momentum state. Here we study scattering between off-resonant light and atoms in a quasi-homogeneous Bose gas with tunable interactions and show that even weak interactions, which essentially do not alter the momentum distribution, strongly affect atom–light scattering. Changes in local atomic correlations suppress the bosonic enhancement under weak repulsive interactions and increase the scattering rate under attractive ones. Moreover, if the interactions are rapidly tuned, light scattering reveals correlation dynamics that are orders of magnitude faster than the collisional dynamics of the momentum-space populations. Its extreme sensitivity to correlation effects makes off-resonant light scattering a powerful probe of many-body physics in ultracold atomic gases.