Austrian Academy of Sciences
Wednesday, November 18, 2020
Entanglement has become one of the essential features in quantum science and technology. For photons, polarization qubits have become an essential workhorse. Recent developments opened up qubits which are defined in a two-dimensional Hilbert space. Recently, a new field opened up where photons can be created in an in principle infinite discrete state space using their orbital angular momentum (OAM). Most interesting are multi-particle multi-photon entangled states which can be generated by using a new concept: entanglement by path identity. It has been shown that two photons can be entangled in up to 100 dimensions and can carry very high quantum numbers, the current limit being above ten thousand. Interesting phenomena already arise for product states of photons because of the non-assignability of a common phase to individual photons. This leads to interesting imaging possibilities where the photons registered on a camera never interacted with the object. There are also very interesting which-path information issues involved, which are related to quantum eraser, which lead to quantum eraser ideas. A most interesting application is the phenomenon of entanglement swapping, where the results of photon measurements at an earlier time can be interpreted as being due to entanglement or not, depending on some later measurements. I will conclude with some more recent experiments on creating three-particle GHZ states and on teleporting three-dimensional states.