Observation of vortices in a dipolar supersolid

Supersolids are states of matter that spontaneously break two continuous symmetries: translational invariancedue to the appearance of a crystal structure and phase invariance due to phase locking of single-particle wavefunctions, responsible for superfluid phenomena. While originally predicted to be present in solid helium,ultracold quantum gases provided a first platform to observe supersolids, with particular success comingfrom dipolar atoms. Phase locking in dipolar supersolids has been probed through e.g. measurements ofthe phase coherence and gapless Goldstone modes, but quantized vortices, a hydrodynamic fingerprint ofsuperfluidity, have not yet been observed. Here, with the prerequisite pieces at our disposal, namely a method togenerate vortices in dipolar gases and supersolids with two-dimensional crystalline order, we report onthe theoretical investigation and experimental observation of vortices in the supersolid phase. Our work revealsa fundamental difference in vortex seeding dynamics between unmodulated and modulated quantum fluids. Thisopens the door to study the hydrodynamic properties of exotic quantum systems with multiple spontaneouslybroken symmetries, in disparate domains such as quantum crystals and neutron stars.