We review a series of experiments on spatial entanglement, both in two dimensions and in orbital angular moment. Two-photon scattering is introduced as tool to quantify the dimensionality of the entanglement and proof its purity.
We put forward an approach to estimate the amount of bipartite spatial entanglement of down-converted photon states correlated in orbital angular momentum and the magnitude of the transverse (radial) wave vectors. Both degrees of freedom are properly considered in our framework, which only requires azimuthal local linear optical transformations and mode selection analysis with two fiber detectors. The coincidence distributions predicted by our approach give an excellent fit to the distributions measured in a recent experiment aimed to show the very high-dimensional transverse entanglement of twin photons from a down-conversion source. Our estimate for the Schmidt number is substantially lower but still confirms the presence of high-dimensional entanglement.
We report the first quantum entanglement experiment in South Africa. The spatial modes of the entangled photon pair are investigated with their potential for high-dimensional entanglement. The generation, measurement and characterisation of the entangled states are examined in detail, where we show high-dimensional entanglement in a Hilbert space of dimension 25. We highlight the experimental challenges contained within each step and provide practical techniques for future experiments in the quantum regime.
Entanglement contains one of the most interesting features of quantum mechanics, often named quantum non-locality [1,2].This means entangled states are not separable regardless of the spatial separation of their components.Measurement results on one particle of a two-particle entangled state define the state of the other particle instantaneously with neither particle enjoying its own well-defined state before the measurement.So far experimental confirmation of entanglement has been restricted to qubits, i.e. two-state quantum systems including recent realization of three-[3, 4] and four-qubit [5,6] entanglements.Yet, an ever increasing body of theoretical work calls for entanglement in quantum system of higher dimensions [7,8].For photons one is restricted to qubits as long as the entanglement is realized using the photons polarization.Here we report the first realization of entanglement exploiting the orbital angular momentum of photons,