  We demonstrate a waveplate for a pseudo-spin-1/2 Bose-Einstein condensate
using a two-photon Raman interaction. The angle of the waveplate is set by the
relative phase of the optical fields, and the retardance is controlled by the
pulse area. The waveplate allows us to image maps of the Stokes parameters of a
Bose-Einstein condensate and thereby measure its relative ground state phase.
We demonstrate the waveplate by measuring the Stokes parameters of a coreless
vortex.
