Dimensional control of the coherence time of scattered light in cold atom clouds

Cold atomic clouds are promising platforms for generating correlated photons, but multiple scattering and associated Doppler broadening limit their temporal coherence. Here we demonstrate that cloud geometry provides a powerful means to extend the coherence time of scattered light. In the experiment, intensity-correlation measurements show that an elongated (quasi-1D) cloud exhibits systematically longer coherence times than a spherical (3D) cloud of the same on-axis optical thickness, as a direct consequence of the suppression of multiple scattering in the elongated geometry. Random-walk simulations reproduce this trend and further show that elongation drives the coherence time toward the single-scattering limit. The combined results establish cloud geometry as a robust control parameter for temporal coherence in cold-atom ensembles, with potential applications in quantum optics and communication.