  An increase in the dimension of state space for quantum key distribution
(QKD) can decrease its fidelity requirements while also increasing its
bandwidth. A significant obstacle for QKD with qudits (d>2) has been an
efficient and practical quantum state sorter for photons whose complex fields
are modulated in both amplitude and phase. We propose such a sorter based on a
multiplexed thick hologram, constructed e.g. from photo-thermal refractive
(PTR) glass. We validate this approach using coupled-mode theory with
parameters consistent with PTR glass to simulate a holographic sorter. The
model assumes a three-dimensional state space spanned by three tilted
planewaves. The utility of such a sorter for broader quantum information
processing applications can be substantial.
