Notable early achievements while at DERA included demonstrations of quantum interference and non-locality over large distances, demonstrating a violation of Bell's Inequality over 4 km of optical fibre in 1994. These experiments were followed by work in quantum cryptography, resulting in his team at DERA setting a world record of 1.9 km range for free space secure quantum cryptography. A collaboration with Ludwig-Maximilian University, Munich in 2002 successfully demonstrated an open air quantum cryptography experiment over a distance of 23.4 km.