Entangled photons can be used to make measurements with an accuracy beyond that possible with classical light. While most implementations of quantum metrology have used states made up of a single colour of photons, we show that entangled states of two colours can show supersensitivity to optical phase and path-length by using a photonic crystal fibre source of photon pairs inside an interferometer. This setup is relatively simple and robust to experimental imperfections. We demonstrate sensitivity beyond the standard quantum limit and show super-resolved interference fringes using entangled states of two, four, and six photons.
@article{arxiv.1308.2527,
title = {Multi-Colour Quantum Metrology with Entangled Photons},
author = {Bryn Bell and Srikanth Kannan and Alex McMillan and Alex S. Clark and William J. Wadsworth and John G. Rarity},
journal= {arXiv preprint arXiv:1308.2527},
year = {2013}
}