Using a spontaneous-downconversion photon source, we produce true non-maximally entangled states, i.e., without the need for post-selection. The degree and phase of entanglement are readily tunable, and are characterized both by a standard analysis using coincidence minima, and by quantum state tomography of the two-photon state. Using the latter, we experimentally reconstruct the reduced density matrix for the polarization. Finally, we use these states to measure the Hardy fraction, obtaining a result that is 122σ from any local-realistic result.
@article{arxiv.quant-ph/9908081,
title = {Non-maximally entangled states: production, characterization and utilization},
author = {Andrew G. White and Daniel F. V. James and Philippe H. Eberhard and Paul G. Kwiat},
journal= {arXiv preprint arXiv:quant-ph/9908081},
year = {2009}
}