We report a controllable method for producing mixed two-photon states via Spontaneous Parametric Down-Conversion with a two-type-I crystal geometry. By using variable polarization rotators (VPRs), one obtains mixed states of various purities and degrees of entanglement depending on the parameters of the VPRs. The generated states are characterized by quantum state tomography. The experimental results are found to be in good agreement with the theory. The method can be easily implemented for various experiments which require the generation of states with controllable degrees of entanglement or mixedness.
@article{arxiv.1304.2101,
title = {Controllable generation of mixed two-photon states},
author = {Jibo Dai and Yink Loong Len and Yong Siah Teo and Leonid A. Krivitsky and Berthold-Georg Englert},
journal= {arXiv preprint arXiv:1304.2101},
year = {2015}
}