Charles H. Bennett and Gilles Brassard have been named recipients of the 2025 ACM A.M. Turing Award, computing's highest honour. The recognition marks a watershed moment for quantum information science, a field that barely existed four decades ago and now underpins everything from secure communications to the next generation of supercomputers.
Bennett, an American physicist at IBM Research, and Brassard, a Canadian computer scientist at the Université de Montréal, are widely recognised as founders of quantum information science, a field at the intersection of physics and computer science that treats quantum mechanical phenomena not merely as properties of matter, but as resources for processing and transmitting information. The award carries a $1 million prize with financial support provided by Google, Inc.
The two researchers met by chance in 1979 at a conference in Puerto Rico. Bennett and Brassard met at a 1979 computer science conference in Puerto Rico and hit it off as professional collaborators. By 1982, the duo co-authored a first-of-its-kind quantum cryptography paper with Wiesner. Two years later came their breakthrough: they introduced the first practical quantum cryptography protocol, called "BB84" for "Bennett-Brassard 1984." The work showed that two parties, i.e. "Alice" and "Bob," could establish a secret key with security rooted in the laws of physics rather than potentially shaky assumptions about the difficulty of a particular computation.
This was radical. Traditional encryption relies on mathematical assumptions that a particular problem is hard to solve. Quantum cryptography offers something far stronger: BB84 achieves information-theoretic security without computational assumptions, instead relying on a fundamental property of quantum information: it cannot be copied or measured without disturbance. Any attempt at eavesdropping leaves detectable traces before any information can be compromised. Variants of BB84 have already been implemented in operational quantum communication networks around the world, using both landlines via fibre and free space communication through satellites.
What distinguished Bennett and Brassard was their ability to move from theory to practice. Bennett and then-summer student John Smolin, now an IBM researcher, built the first quantum cryptography apparatus in Bennett's office, and joined by Brassard, carried out the first demonstration of BB84 in 1989. They made the custom two-metre-long device out of mirrors, polarisers, and photon detectors and ran it with software written by Brassard and his students. This was not a paper result filed away in a journal. It worked.
Their contributions extended far beyond cryptography. Bennett also co-authored a landmark 1993 study introducing quantum teleportation, which showed how an unknown quantum state could be transmitted using entanglement and classical communication, turning a once-philosophical curiosity into a practical resource for quantum engineering. Their subsequent work on entanglement distillation in 1996 demonstrated how imperfect entanglement could be strengthened into high-quality entanglement, a critical step toward scalable quantum communication. These ideas underpin ongoing efforts to build quantum networks and ultimately a quantum internet capable of transmitting quantum information across global distances.
The award itself signals something broader about how science is valued. Over four decades, Bennett and Brassard's collaboration bridged two previously distinct disciplines: physics and computer science. By incorporating quantum principles into computational models, their work has influenced cryptography, algorithm design, computational complexity, learning theory, interactive proofs, and mathematical physics. Their research helped catalyse a generation of physicists and computer scientists to work across disciplinary boundaries.
Bennett has said the award "establishes the importance both in theory and in practice of studying the physics of information processing." Their recognition comes on the heels of the United Nations' designation of 2025 as the International Year of Quantum Science and Technology, reflecting the growing global investment in quantum computing, communication, and sensing.
Few prizes recognise the moment when theoretical insight becomes technological reality. This one does. Quantum information science began as a curiosity about what the laws of physics might allow. Today it is reshaping how humanity secures information, computes, and communicates. Bennett and Brassard spent decades asking the right questions when few others thought to ask them at all.