We report an experimental implementation of deterministic preparation and measurement of single-photon two-qubit entangled states, in which the polarization and the spatial modes of a single-photon each represent a quantum bit. It is demonstrated that all four single-photon two-qubit entangled states (Bell states) can be easily prepared and measured deterministically using linear optical elements alone. We also discuss how this scheme can be used for implementing recently proposed single-photon two-qubit quantum cryptography.
Yoon-Ho Kim, Yoon-Ho Kim,
"Single-photon two-qubit entangled states: preparation and measurement", Proc. SPIE 5551, Quantum Communications and Quantum Imaging II, (19 October 2004); doi: 10.1117/12.561343; https://doi.org/10.1117/12.561343