We report interferometric schemes to prepare arbitrary states of four-dimensional qudits (ququarts) based on biphoton states of ultrafast-pumped frequency-nondegenerate spontaneous parametric down-conversion. Preparation and tomographic characterization of a few examples of general single-ququart states, a pure state, a completely mixed state, and a partially-mixed state, are experimentally demonstrated.
@article{arxiv.0804.3327,
title = {Preparation and characterization of arbitrary states of four-dimensional qudits based on biphotons},
author = {So-Young Baek and Stanislav S. Straupe and Alexander P. Shurupov and Sergei P. Kulik and Yoon-Ho Kim},
journal= {arXiv preprint arXiv:0804.3327},
year = {2009}
}