Entangled vector vortex beams

Light beams having a vectorial field structure, or polarization, that varies over the transverse profile anda central optical singularity are called vector vortex (VV) beams and may exhibit specific properties such asfocusing into “light needles” or rotation invariance. VV beams have already found applications in areas rangingfrom microscopy to metrology, optical trapping, nano-optics, and quantum communication. Individual photonsin such beams exhibit a form of single-particle quantum entanglement between different degrees of freedom. Onthe other hand, the quantum states of two photons can be also entangled with each other. Here, we combine thesetwo concepts and demonstrate the generation of quantum entanglement between two photons that are both in VVstates: a form of entanglement between two complex vectorial fields. This result may lead to quantum-enhancedapplications of VV beams as well as to quantum information protocols fully exploiting the vectorial features of light