When physicists got their first insights into the quantum world more than a century ago, they found it puzzling to say the least. But gradually, and through clever theoretical and experimental work, a consistent quantum theory emerged.

Two physicists that who played crucial roles in this evolution were Albert Einstein and John Bell. In this episode of the Physics World Weekly podcast the theoretical crypto-physicist Artur Ekert explains how a quantum paradox identified by Einstein and colleagues in 1935 inspired a profound theoretical breakthrough by Bell three decades later.

Ekert, who splits his time between the University of Oxford and the National University of Singapore, describes how he used Bell’s theorem to create a pioneering quantum cryptography protocol and he also chats about current research in quantum physics and beyond.

This article forms part of Physics World‘s contribution to the 2025 International Year of Quantum Science and Technology (IYQ), which aims to raise global awareness of quantum physics and its applications.

Stayed tuned to Physics World and our international partners throughout the next 12 months for more coverage of the IYQ.

Find out more on our quantum channel.