We propose an all-optical setup, which couples different degrees of freedom of a single photon, to investigate entanglement generation by a common environment. The two qubits are represented by the photon polarization and Hermite-Gauss transverse modes, while the environment corresponds to the photon path. For an initially two-qubit separable state, the increase of entanglement is analyzed, as the probability of an environment-induced transition ranges from zero to one. An entanglement witness that is invariant throughout the evolution of the system yields a direct measurement of the concurrence of the two-qubit state.
@article{arxiv.0910.5754,
title = {Environment-induced entanglement with a single photon},
author = {Malena Hor-Meyll and Adriana Auyuanet and Carolina Borges and Adriano Aragão and José Augusto Huguenin and Antonio Khoury and Luiz Davidovich},
journal= {arXiv preprint arXiv:0910.5754},
year = {2009}
}