Quasiperiodic boundary conditions for three-dimensional superfluids

We derive boundary conditions that allow a three-dimensional periodic array of superfluid vortices to be modeled in a Cartesian domain. The method is applicable to vortices in the Gross-Pitaevskii description of a superfluid and to fluxtubes in the Ginzburg-Landau description of a superconductor. Unlike standard methods for modeling infinite arrays of vortices, the boundary conditions can be used to study the three-dimensional tangling and reconnection of vortex lines expected in superfluid turbulence. In the two-dimensional case, the boundary conditions include two parameters that determine the lattice offset, which for a single superfluid is essentially arbitrary. In the three-dimensional case the boundary conditions include three parameters that must satisfy a particular linear relationship. We present an algorithm for finding all vortex lattice states within a given domain. We demonstrate the utility of the boundary conditions in two specific problems with imperfect or tangled lattices.