Entanglement distillation by Hong-Ou-Mandel interference with orbital angular momentum states

Abstract

Entanglement is an invaluable resource to various quantum communication, metrology, and computing processes. In particular, spatial entanglement has become topical, owing to its wider Hilbert space that allows photons to carry more information. However, spatial entanglement is susceptible to decay in the presence of external perturbations such as atmospheric turbulence. Here we show theoretically and experimentally that in a weak turbulence regime, maximally entangled states can be distilled through quantum interference. We generated entangled photons by spontaneous parametric down-conversion, with one photon in the entangled pairs being sent through a turbulent channel. We recombined the paths of the two photons at a beam-splitter in a Hong-Ou-Mandel interference setup and measured in coincidence, using spatial filters, the spatial correlations between photons in the output ports of the beam-splitter. We performed a state tomography and show that, from an ensemble of pure states with very low levels of entanglement, we distil entangled states with fidelities F ≥ 0.90 with respect to the singlet Bell state.