Phys. Rev. Lett. 122, 013601 (2019)

Vector beams, in particular vector vortex beams, have recently found many applications because of their unusual focusing and symmetry properties. However, to maximize their potential for use in quantum optics, control over two-photon quantum interference between these beams is important, especially for applications such as quantum communication, sensing and metrology. Now, Vincenzo D’Ambrosio and colleagues from Spain and Italy have demonstrated that a q-plate made of an inhomogeneous liquid-crystal slab can provide tunable quantum interference for such beams. The team tune the birefringent phase shift of the q-plate via an externally controlled voltage and an offset angle (in this experiment, 0 and π/4) to modify the amount of quantum interference between the two structured photons and also control the quantum phase in the output state.