Observation of Half-Quantum Vortices in Topological Superfluid 3He

One of the most sought-after objects in topological quantum-matter systems is a vortex carrying half a quantum of circulation. They were originally predicted to exist in superfluid He-3-A but have never been resolved there. Here we report an observation of half-quantum vortices (HQVs) in the polar phase of superfluid He-3. The vortices are created with rotation or by the Kibble-Zurek mechanism and identified based on their nuclear magnetic resonance signature. This discovery provides a pathway for studies of unpaired Majorana modes bound to the HQV cores in the polar-distorted A phase.