A quantum cryptography scheme based on entanglement between a single particle state and a vacuum state is proposed. The scheme utilizes linear optics devices to detect the superposition of the vacuum and single particle states. Existence of an eavesdropper can be detected by using a variant of Bell's inequality.
@article{arxiv.quant-ph/0301131,
title = {Quantum Cryptography Using Single Particle Entanglement},
author = {Jae-Weon Lee and Eok Kyun Lee and Yong Wook Chung and Hai-Woong Lee and Jaewan Kim},
journal= {arXiv preprint arXiv:quant-ph/0301131},
year = {2009}
}