Quantum vortices with half the quantum circulation, known as half-quantum vortices (HQVs), have been observed in various spinor superfluid systems recently. Because of their nonsingular cores, the interaction of HQVs is expected to be different from that of vortices in a conventional scalar superfluid, which can lead to a new class of superfluid dynamics. Here, we report on a collision experiment of two HQV pairs in an antiferromagnetic spinor Bose-Einstein condensate. The observed scattering motions of the HQVs reveal the short range interactions that arise from their ferromagnetic cores. Additionally, we investigate the relaxation dynamics of turbulent superflow containing many HQVs to find that spin wave excitations are generated and maintained by the collisional motions of the HQVs during dissipative evolution. These results provide new insight into the vortex dynamics in spinor superfluids.
We report theoretical results for the stability of half-quantum vortices (HQVs) in the superfluid phases of
3He confined in highly anisotropic Nafen aerogel. Superfluidity of
3He confined in Nafen is the realization of a ``nematic superfluid'' with Cooper pairs condensed into a single
p-wave orbital aligned along the anisotropy axis of the Nafen aerogel. In addition to the nematic phase, we predict a second ``chiral'' phase that onsets at a lower transition temperature. This chiral phase spontaneously breaks time-reversal symmetry and is a topological superfluid. Both superfluid phases are equal-spin pairing condensates that host arrays of HQVs as equilibrium states of rotating superfluid
3He. We present results for the structure of HQVs, including magnetic and topological signatures of HQVs in both the nematic and chiral phases of
3He-Nafen.