The heralded generation of entangled states is a long-standing goal in quantum information processing, because it is indispensable for a number of quantum protocols. Polarization entangled photon pairs are usually generated through spontaneous parametric down-conversion, but the emission is probabilistic. Their applications are generally accompanied by post-selection and destructive photon detection. Here, we report a source of entanglement generated in an event-ready manner by conditioned detection of auxiliary photons. This scheme benefits from the stable and robust properties of spontaneous parametric down-conversion and requires only modest experimental efforts. It is flexible and allows the preparation efficiency to be significantly improved by using beamsplitters with different transmission ratios. We have achieved a fidelity better than 87% and a state preparation efficiency of 45% for the source. This could offer promise in essential photonics-based quantum information tasks, and particularly in enabling optical quantum computing by reducing dramatically the computational overhead.
@article{arxiv.1007.2510,
title = {Experimental demonstration of a heralded entanglement source},
author = {Claudia Wagenknecht and Che-Ming Li and Andreas Reingruber and Xiao-Hui Bao and Alexander Goebel and Yu-Ao Chen and Qiang Zhang and Kai Chen and Jian-Wei Pan},
journal= {arXiv preprint arXiv:1007.2510},
year = {2012}
}