Exploring the BEC-droplet crossover using Rayleigh superradiant scattering

We examine the transition from a Bose-Einstein condensate (BEC) to the quantum droplet of 166Er atoms using Rayleigh superradiant scattering. The efficiency of superradiant scattering demonstrates a similar non-monotonic pattern as the expansion rate of the sample, suggesting that it reflects the original quantum state of the elongated sample. This novel approach enables us not only to investigate the droplet-BEC transition with varying atom numbers but also to monitor the shift of phase transition points with different magnetic field directions. Our work provides insights into the crossover between BEC and droplets and the underlying physics that governs this transition.