  There has been a recent tendency to apply Schroedinger's wave equation to
macroscopic domains, from Bose-Einstein condensates in neutron stars to
planetary orbits. In these applications a hydrodynamical interpretation,
involving vortices in some 'fluid' medium is often given. The vortex picture
appears surprising in light of more traditional interpretations of
Schroedinger's equation, and indeed often appears to rely on ad hoc analogies.
The purpose of this letter is to examine the vortex hypothesis in light of a
simple, transparent mathematical framework. We find that Schroedinger's
equation implies waves can be vortices also for a class of wave functions.
Vortices occur in pairs that perform a sort of quantum computation by
collapsing into either 0 or 1. Vortices collapsing to 0 ('0-vortices') are
longer-lived, and their ratio to 1-vortices is discussed.
