Quantum entanglement of the spin and orbital angular momentum of photons using metamaterials The article doesn't say it, but this sounds like what is known as a "topologically protected" entanglement, which is the most robust known. Physicists have also figured out how to bend light around even a 60 degree angle using topologically protected states. Optical metamaterials can do fantastic things, but the ability to entangle photons like this means the sky is the limit, and circuitry like this can be combined with plasmonics, spintronics, valleytronics, or any number of different quantum circuitry to produce, among other things, something like Mr Spock's tricorder, but much more high tech. Entangled photons would be perfect for solar power. The same research going into these kinds of optical metamaterials can be applied to anything including the internet, VR waveguides, or anything imaginable and many have said that optics will soon eclipse electronics. I'm talking optics you never dreamed were possible, including being able to see what color ultraviolet light actually is.
Free pdf of full paper: https://phsites.technion.ac.il/publications/msegev/Stav_Science_361_1101_2018.pdf
4 bell states? That "study" isnt what you think it is. Need to see the actual experiments, 3 pages isnt a full paper