Advances in high-dimensional quantum entanglement (Englisch)

Since its discovery, quantum entanglement has challenged some of the best established views of the world: locality and reality. Quantum technologies promise to revolutionize computation, communication, metrology and imaging. Here we review conceptual and experimental advances in complex entangled systems involving many multilevel quantum particles. We provide an overview of the latest technological developments in the generation and manipulation of high-dimensionally entangled photonic systems encoded in various discrete degrees of freedom such as path, transverse spatial modes or time–frequency bins. This overview should help to transfer various physical principles for the generation and manipulation from one degree of freedom to another and thus inspire new technical developments. We also show how purely academic questions and curiosity led to new technological applications. Fundamental research provides the necessary knowledge for upcoming technologies, such as a prospective quantum internet or the quantum teleportation of all information stored in a quantum system. Finally, we discuss some important problems in the area of high-dimensional entanglement and give a brief outlook on possible future developments.

The study of higher-dimensional quantum states has seen numerous conceptual and technological developments. This review discusses various techniques for the generation and processing of qudits, which are stored in the momentum, path, time-/frequency-bins, or the orbital angular momentum of photons.

High-dimensional quantum entanglement provides a playground for fundamental research and also leads to technological advances. Examples include stronger violations of local realistic world views that can be exploited to tolerate larger amounts of noise in quantum communication protocols.

Different physical concepts underlie the creation of high-dimensionally entangled photon pairs. Conservation laws result in correlations that if coherent in turn yield high-dimensionally entangled photon pairs. Multiple indistinguishable and coherent possibilities can be combined such that custom-tailored, high-dimensional entanglement is created.

Various physical and technical approaches on how to manipulate multilevel quantum states in different degrees of freedom (DoFs) are presented. Concepts used in one DoF may also be applied to other DoFs, inspiring new synergies that create new technologies.

Current advances in experimental methods for generating high-dimensional multiphoton entanglement enable future technologies, such as teleporting the complete quantum information stored in a single photon.