Improvement of an atomic measurement by multi-photon interference

NOON states are a class of path entangled or polarization entangled states consisting of N photons that achieves better performance in phase estimation compared to coherent states as input. This experiment demonstrates for the first time the use of multi-photon interference to improve an atomic measurement. The generated NOON states are narrow-band, bright, rubidium-tuned, have a high fidelity and therefore represent an ideal tool for studying the interaction between photons and atoms.