Biphoton ququarts and their entanglement
Yoon-Ho Kim · 2007
A four-dimensional quantum system (ququart) can be constructed by using the biphoton polarization states of frequency-nondegenerate spontaneous parametric down-conversion. We first discuss how to generate and characterize general single-ququart states with varying degrees of mixedness. We then discuss schemes to entangle multiple biphoton ququarts using linear optics and coincidence post-selection.