Vortex pair dynamics in homogeneous dipolar superfluids

The static and dynamic properties of vortices in dipolar Bose-Einstein condensates (dBECs) can be considerably modified relative to their nondipolar counterparts by the anisotropic and long-ranged nature of the dipole-dipole interaction. In a uniform dBEC, we analyze the structure of single vortices and the dynamics of vortex pairs, investigating the deviations from the nondipolar paradigm. For a straight vortex line, we find that the induced dipolar interaction potential is axially anisotropic when the dipole moments have a nonzero projection orthogonal to the vortex line. This results in a corresponding elongation of the vortex core along this projection as well as an anisotropic superfluid phase and enhanced compressibility in the vicinity of the vortex core. Consequently, the trajectories of like-signed vortex pairs are described by a family of elliptical and oval-like curves rather than the familiar circular orbits. Similarly for opposite-signed vortex pairs their translation speeds along the binormal are found to be dipole interaction-dependent. The insights gleaned from this idealised system are subsequently applied to the problem of vortex reconnections in dBECs arising from the Crow instability of mutually out-of-phase Kelvin wave excitations on a pair of antiparallel vortex lines. We find that both the time taken for the first reconnection to occur and the wavelength of the maximally unstable Kelvin mode are dipole moment-dependent, thereby mediating the size of the vortex loops formed during subsequent reconnections. We expect that these findings will shed light on the underlying mechanisms of many-vortex phenomena in dBECs such as quantum turbulence and the dynamics of vortex lattices.