The paper by Alois Mair, Alipasha Vaziri, Gregor Weihs, and Anton Zeilinger reports the first realization of entanglement using the orbital angular momentum (OAM) of photons, which are states of the electromagnetic field with phase singularities (doughnut modes). This approach opens up a practical method for multi-dimensional entanglement, where the entangled states consist of multiple orthogonal states. The authors confirm that spontaneous parametric down-conversion conserves the OAM of photons by demonstrating that the state of the down-converted photons cannot be explained by classical correlation. They show that the down-converted photon pairs are a coherent superposition of various combinations allowed by angular momentum conservation, thus proving entanglement in their OAM. The experimental setup involves using Laguerre-Gaussian (LG) modes and computer-generated holograms to detect the down-converted photons, confirming the conservation of OAM and the entanglement of the photon states. The results have implications for quantum computation, quantum communication, and potential applications in quantum cryptography and micro-machining.The paper by Alois Mair, Alipasha Vaziri, Gregor Weihs, and Anton Zeilinger reports the first realization of entanglement using the orbital angular momentum (OAM) of photons, which are states of the electromagnetic field with phase singularities (doughnut modes). This approach opens up a practical method for multi-dimensional entanglement, where the entangled states consist of multiple orthogonal states. The authors confirm that spontaneous parametric down-conversion conserves the OAM of photons by demonstrating that the state of the down-converted photons cannot be explained by classical correlation. They show that the down-converted photon pairs are a coherent superposition of various combinations allowed by angular momentum conservation, thus proving entanglement in their OAM. The experimental setup involves using Laguerre-Gaussian (LG) modes and computer-generated holograms to detect the down-converted photons, confirming the conservation of OAM and the entanglement of the photon states. The results have implications for quantum computation, quantum communication, and potential applications in quantum cryptography and micro-machining.