In findings recently published in Nature Photonics, a team including researchers from the UK, the Netherlands and Photon Sciences division head Gabriel Aeppli have investigated multi-photon THz absorption in Si:P. Their studies, using the THz free-electron laser FELIX, discovered a two photon absorption cross-section ten orders of magnitude higher than that of a natural hydrogen atom and may enable new methods in quantum control. In addition to the original publication their findings are also discussed in a 'News and Views' article.