Quantum computation with photons requires efficient two photon gates. We put forward a two photon entangling gate which uses an intermediate atomic system. The system includes a single Rydberg atom which can switch on and off photon absorption in an ensemble using the dipole blockade. The gate is based in a counterfactual protocol. The mere possibility of an absorption that can only occur with a vanishing probability steers the photons to the desired final state.
@article{arxiv.1111.4671,
title = {A counterfactual Rydberg gate for photons},
author = {Juan Carlos Garcia-Escartin and Pedro Chamorro-Posada},
journal= {arXiv preprint arXiv:1111.4671},
year = {2015}
}