We present an implementation of photonic qubit precertification that performs the delicate task of detecting the presence of a flying photon without destroying its qubit state, allowing loss-sensitive quantum cryptography and tests of nonlocality even over long distance. By splitting an incoming single photon in two via parametric down-conversion, we herald the photon's arrival from an independent photon source while preserving its quantum information with up to 92.3±0.6 % fidelity. With reduced detector dark counts, precertification will be immediately useful in quantum communication.
@article{arxiv.1510.04531,
title = {Certifying the presence of a photonic qubit by splitting it in two},
author = {Evan Meyer-Scott and Daniel McCloskey and Klaudia Gołos and Jeff Z. Salvail and Kent A. G. Fisher and Deny Hamel and Adán Cabello and Kevin J. Resch and Thomas Jennewein},
journal= {arXiv preprint arXiv:1510.04531},
year = {2016}
}