We analyse the distribution of secure keys using quantum cryptography based on the continuous variable degree of freedom of entangled photon pairs. We derive the information capacity of a scheme based on the spatial entanglement of photons from a realistic source, and show that the standard measures of security known for quadrature-based continuous variable quantum cryptography (CV-QKD) are inadequate. A specific simple eavesdropping attack is analysed to illuminate how secret information may be distilled well beyond the bounds of the usual CV-QKD measures.
@article{arxiv.0711.4631,
title = {On Secure Quantum Key Distribution Using Continuous Variables of Single Photons},
author = {Lijian Zhang and Christine Silberhorn and Ian A. Walmsley},
journal= {arXiv preprint arXiv:0711.4631},
year = {2009}
}