Figure 2. Experimental realization of Bloch oscillations of two-photon N00N states.
(a) Spatial correlations measurement set-up. Photon pairs are produced by type-I spontaneous parametric down-conversion and single-photon detection is achieved using avalanche photodiodes. (b) Femtosecond-laser-written photonic circuit made of two functional sections: A two-photon N00N state with arbitrary symmetry is first prepared in a detuned directional coupler, and subsequently evolves in a Bloch oscillator emulated by a curved array. (c) Preparation of two-photon N00N state with arbitrary phase shift φ, achieved by detuning the propagation constant by Δβ in one of the two arms of a 50:50 directional coupler. (d) Radius of curvature RC of waveguides arranged in a curved array necessary for reaching a specific point along the Bloch cycle.