In this presentation, the observation of vortices in He droplets is discussed. For this purpose, droplets have been doped with a large number of Xe atoms and imaged via X-­ray diffraction at the Linac Coherent Light Source at SLAC National Accelerator Laboratory. Quantum vortices in He droplets are expected to attract Xe atoms and serve as nucleation centers for the growth of Xe clusters. Therefore, obtaining the positions of clusters inside individual droplets may help in deducing the number and configuration of vortices within. In small droplets of about 200 nm in diameter, certain diffraction images show clear interference patterns with characteristic contributions from both the droplet and embedded Xe clusters. We have created simulated diffraction images, using a model of scattering from multiple clusters (He droplet and several Xe clusters), which gave very good agreement with some characteristic experimental images. These results indicate the presence of several Xe clusters separated by ~100 nm within the droplet, consistent
with the binding of Xe clusters to a few vortices in small droplets. In larger droplets of about 2 μm in diameter, the diffraction images often show Bragg spots, a strong indication of an extended lattice. This is consistent with the formation of Abrikosov arrays consisting of about 100 parallel vortices.

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