Charles H. Bennett and Gilles Brassard were named recipients of the 2025 ACM A.M. Turing Award for foundational work in quantum information science. The Association for Computing Machinery recognised their development of quantum cryptography, including the 1984 technique known as BB84, as a major advance in secure communication and computing.
The award, named for mathematician and codebreaker Alan Turing and often compared with a Nobel Prize for computing, carries $1 million. Bennett, 82, is an IBM fellow in New York. Brassard, 70, is a professor at the University of Montreal. Their collaboration began after a chance meeting at a conference in Puerto Rico in 1979.
Bennett reportedly approached Brassard while they were swimming during a break and suggested creating a banknote that could not be counterfeited. That conversation started decades of joint research into how the rules of quantum physics might protect information. Their eventual method encoded a cryptographic key in quantum states rather than relying solely on hard mathematical problems.
Conventional encryption commonly depends on calculations that are difficult for today's computers to reverse. Researchers expect sufficiently capable quantum computers to weaken some of those widely used systems. BB84 takes a different approach: an attempt to measure or copy the quantum states carrying the key changes them. The communicating parties can therefore detect signs that a third party has intercepted the exchange before trusting the key.
That property does not make every system using quantum technology automatically secure, nor does it remove practical challenges in equipment and implementation. The available reporting described the underlying protocol and its importance but did not claim that all current digital communications can immediately adopt it. ACM instead framed the work as a route toward protecting data exchanges in the decades ahead.
The pair's research sits at the intersection of physics and computer science. It helped turn quantum behaviour—once studied mainly as a description of particles such as photons and electrons—into a resource for processing and securing information. The award also reflects the long interval between basic theory and recognition for technology that may become more important as quantum computing develops.
By honouring Bennett and Brassard together, ACM credited both the conception of quantum cryptography and the collaborative protocol that made its security principle concrete. The significance of BB84 lies in changing the basis of trust: interception can reveal itself through physical disturbance, rather than security depending only on an adversary lacking enough computing power to solve a conventional mathematical challenge. The award therefore recognised a 1984 idea whose strategic relevance has increased as researchers work toward more capable quantum computers.
