Artur Ekert
Polish-born physicist whose E91 protocol bases the security of quantum key distribution on entanglement rather than on single photons.
As a doctoral student at Oxford, Ekert published a protocol in 1991 in which the two parties share entangled particle pairs and test Bell's inequality on a subset of their measurements. If the inequality is violated as quantum mechanics predicts, no third party can have tapped the correlations; if it isn't, someone has been listening. The idea later became the basis of device-independent quantum cryptography, where you don't even have to trust your own hardware.
Ekert stayed at Oxford, where he helped build up quantum computing research in the 1990s, and in 2007 became founding director of the Centre for Quantum Technologies in Singapore. He is one of the few who moves unbothered between the physics department and the cryptography conferences.