Multimode Hong-Ou-Mandel Interferometry
  We review some recent experiments based upon multimode two-photon interference of photon pairs created by spontaneous parametric down-conversion. The new element provided by these experiments is the inclusion of the transverse spatial profiles of the pump, signal and idler fields. We discuss multimode Hong-Ou-Mandel interference, and show that the transverse profile of the pump beam can be manipulated in order to control two-photon interference. We present the basic theory and experimental results as well as several applications to the field of quantum information. 
S. P. Walborn, W. A. T. Nogueira, A. N. de Oliveira, S. P\'adua, C. H.   Monken