Prof. Madsen is co-founder and group leader in the ALPHA collaboration that was the first to trap antihydrogen and observe resonant quantum transitions. He has been actively involved in antihydrogen research since 2001, playing a substantial role in the ATHENA team that first formed low energy antihydrogen in 2002. As Professor at Swansea University he has a research group at CERN. His group led the effort to implement several key techniques leading to the first antihydrogen trapping.