  We present an enhanced version of the Zernike wavefront sensor, that
simultaneously measures phase and amplitude aberrations. The 'vector-Zernike'
wavefront sensor consists of a patterned liquid-crystal mask, which imposes
$\pm \pi/2$ phase on the point spread function core through the achromatic
geometric phase acting with opposite sign on opposite circular polarizations.
After splitting circular polarization, the ensuing pupil intensity images are
used to reconstruct the phase and the amplitude of the incoming wavefront. We
demonstrate reconstruction of the complex wavefront with monochromatic lab
measurements and show in simulation the high accuracy and sensitivity over a
bandwidth up to $100\%$
