Entanglement in Classical Light
Eileen Otte · Springer theses · 2020
Within previous chapters the ability to customize complex singular light fields in its various properties has been demonstrated. Intriguing light fields structured in 2d, 3d or even 4d have been presented giving new insights into the fundamental properties of singular light and paving the way to pathbreaking applications, e.g., in optical micromanipulation or to the implementation of functional 4d materials. However, there is another property enlarging the already rich phenomenology of structured light and opening up new perspectives for applied optics: so-called classical entanglement . Entanglement is today considered as a property typically associated to quantum mechanics. This property is essential for prominent quantum observations and studies as the Gedankenexperiment of Schrödinger’s cat [ 1 , 2 ], the Einstein–Podolsky–Rosen paradox [ 3 ], Bell’s inequality [ 4 ], quantum cryptography [ 5 ], or quantum computing [ 6 , 7 ]. However, it became clear that the algebraic concept underlying entanglement can indeed be created in classical optics, facilitating the classical analogon of quantum entanglement, thus, bridging a gap between classical and quantum optics. The analogon displays essential quantum mechanical features of entanglement as the key feature of non-separability. For example structured light, namely, vectorial beams can be described as classically entangled, being non-separable in its polarization and spatial shape, as it will be shown in the following section.