Long-range quantum order underlies a number of related physical phenomena including superfluidity, superconductivity, the Higgs mechanism, Bose-Einstein condensates, and spin systems. While superfluidity in Helium-4 was one of the earliest discovered of these, it is not the best understood, owing to locally-strong interactions which make theoretical progress difficult, and a lack of local experimental probes. Our group discovered that micron-sized hydrogen particles, and most recently fluorescent nanoparticles, may be used to label quantized vortices in flows of superfluid helium. Particles not on vortices trace the motion of the normal component of the superfluid. This diagnostic tool has given us a new perspective on an old subject.