We discuss our experimental efforts for generating and measuring four-photon entangled states, entangled in the orbital angular momentum space (OAM). For OAM space photons can be described in a...Show moreWe discuss our experimental efforts for generating and measuring four-photon entangled states, entangled in the orbital angular momentum space (OAM). For OAM space photons can be described in a high-dimensional Hilbert space. In order to generate the four-photon states, we use the process of spontaneous parametric down-conversion (SPDC) in a PPKTP crystal. Further a theoretical description on entangled states, Gaussian modes and SPDC is stated.Show less