  In low-temperature superfluid helium, viscosity is zero, and vorticity takes
the form of discrete, vortex filaments of fixed circulation and atomic
thickness. We present numerical evidence of three-dimensional inverse energy
transfer from small length scales to large length scales in superfluid
turbulence generated by a flow of vortex rings. We argue that the effect arises
from the anisotropy of the flow, which favours vortex reconnections of vortex
loops of the same polarity, and that it has been indirectly observed in the
laboratory. The effect open questions about analogies with related processes in
ordinary turbulence.
