I will present the experimental implementation of a probabilistic linear optical controlled phase gate. It is operating on the polarization degree of freedom of photons and is based on the second order interference at a ‘magic’ beam splitter. We characterized the gate performance with a tomographic set of measurements and, by fitting a model of the gate to the obtained data, we extracted the corresponding experimental parameters.
In a next step, the controlled phase gate served to entangle two EPR-pairs resulting in a four-photon entangled cluster state with a fidelity of 74.4 ± 1.2 %. We studied the state using entanglement witnesses, showed the violation of a bell inequality and verified its high entanglement persistency against photon loss.
Finally, we demonstrated a teleportation and an entanglement swapping
experiment with a complete bell state analysis that was based on the
controlled phase gate.