Gilles Brassard

ACM A. M. Turing Award

Canada - 2025

READ FULL CITATION AND ESSAY

citation

For their essential role in igniting and shaping the quantum revolution in computer science and in information and communications technology

Charles H. Bennett and Gilles Brassard are the recipients of the 2025 ACM A.M. Turing Award. They are two of the founders of a new field, quantum information science, which lies at the intersection of physics and computer science and has fostered exciting collaborations between scientists in both areas. Further impetus to this development was the concurrent interest in general quantum computation. Quantum information science is a scientifically fundamental and deep topic, with enormous practical relevance. It has motivated and triggered remarkable technological advances, with many foreseen and unforeseen application areas.

Bennett and Brassard’s joint 1984 paper (BB84), “Quantum cryptography: Public key distribution and coin tossing”, inspired by the insights of their late collaborator Stephen Wiesner, is a transformative moment in the history of computer science. It showed that quantum physics can solve a major problem, namely secret communication between parties sharing little or no prior secret information, in a way resilient to adversaries regardless of their computational power and technological sophistication. In his 1949 paper on the optimality of the one-time pad, Shannon proved that this task is impossible to achieve by classical communication alone. Meanwhile, an alternative solution to the key establishment problem, public key cryptography, became the foundation of 21st century cryptography and computer security, resulting in the 2002 and 2015 Turing Awards. It circumvents Shannon impossibility by limiting the computational power of adversaries. Its widespread adoption attests its convenience and compatibility with existing infrastructure, but it rests on a foundation arguably weaker than the correctness of quantum physics, namely the assumed existence of “trapdoor” functions (an assumption stronger than P≠NP). In sharp contrast, the BB84 quantum key establishment protocol achieves information-theoretic security with no computational assumptions, but it requires a special hardware infrastructure.

Ironically, a decade after the invention of BB84, Peter Shor proved that quantum algorithms can quickly factor large integers and compute discrete logarithms, the most used trapdoor functions. Thus the (generally exciting) possibility that quantum computers become practical will undermine today’s security infrastructure, requiring new computational assumptions—the existence of quantum-resistant public key cryptography, again stronger than P≠NP—or alternatively the broader integration of quantum cryptography into that infrastructure. While general quantum computing has not yet been achieved, BB84 has been implemented in large networks across the globe.

Bennett and Brassard’s 1984 paper also goes beyond key establishment, initiating the general theory of quantum cryptography. It presents a quantum protocol for another central cryptographic primitive, collective coin-flipping, but then goes on to explain how that protocol can be subverted by use of quantum entanglement. Doing so was the first demonstration that entanglement is relevant to cryptography, ultimately leading to a mature theory of entanglement-based-quantum cryptography, an approach usefully complementary to the original BB84 key establishment protocol.

In twenty-six joint papers, and in hundreds with other collaborators, Bennett and Brassard continued to explore the new world in which quantum mechanical effects are used in computation and communication. For example, their joint 1993 paper introduced “quantum teleportation”, showing how an arbitrary quantum state can be transmitted using only classical information between entangled parties. This fundamental discovery is at the heart of numerous papers, and its experimental verification was recognized by the 2022 Nobel Prize in physics. Indeed, the study of entanglement, the mysterious and unintuitive notion of quantum correlation, was explored in many of their works. In 1996, Bennett, Brassard, and various collaborators developed the idea of “entanglement distillation”,  showing how to enhance a low-quality entanglement into a near perfect one.

Their body of work, ideas, lectures and students in the past decades has had an enormous influence on the fields of quantum information and quantum computing theories and practice. Within computer science, the introduction of quantum theory into different computational models has influenced many subfields including, besides cryptography, algorithm design, computational complexity, learning theory, interactive proofs, and more, some with surprising consequences in mathematics and mathematical physics.

This lifelong collaboration between a physicist and a computer scientist has led to numerous such collaborations and synergies between these two fields, making the quantum revolution what it is today.

Press Release

2025 ACM A.M. Turing Award

ACM has named Charles H. Bennett and Gilles Brassard as the recipients of the 2025 ACM A.M. Turing Award for their essential role in establishing the foundations of quantum information science and transforming secure communication and computing.

The ACM A.M. Turing Award, often referred to as the “Nobel Prize in Computing,” carries a $1 million prize with financial support provided by Google, Inc. The award is named for Alan M. Turing, the British mathematician who articulated the mathematical foundations of computing.

Bennett and Brassard are widely recognized 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.

In 1984, inspired by the insights of their late collaborator Stephen Wiesner, Bennett and Brassard introduced the first practical protocol for quantum cryptography, now known as BB84. The paper, “Quantum Cryptography: Public Key Distribution and Coin Tossing,” demonstrated that two parties could establish a secret encryption key with security guaranteed by the laws of physics, even against adversaries with unlimited computational power and technological sophistication such as a quantum computer.

In 1949, mathematician and computer scientist Claude Shannon proved that perfect secrecy in communications is only possible between parties who share ahead of time a secret key that is at least as long as the message itself. Public-key cryptography later provided a powerful workaround by relying on mathematical problems which were believed to be hard to solve—assumptions embedded in modern digital infrastructure but shown by Peter Shor as early as 1994 to become insecure when a full-size quantum computer is available. In sharp contrast, 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.

As research advances toward large-scale quantum computers, governments and industry are reassessing the long-term resilience of widely deployed public-key cryptographic systems. Quantum cryptography, alongside emerging, hopefully quantum-resistant classical approaches for which no proofs of security are known, represents one pathway toward securing digital communications in the decades ahead. Variants of BB84 have already been implemented in operational quantum communication networks around the world, using both landlines via fiber and free space communication through satellites.

Beyond cryptography, Bennett and Brassard’s work reshaped the theoretical foundations of computing. In 1993 and with other collaborators, they introduced quantum teleportation, demonstrating how an arbitrary quantum state could be transmitted between distant parties using quantum entanglement—the surprisingly correlated behavior of particles too far apart to influence one another—and classical communication. This discovery showed that entanglement, once viewed primarily as a philosophical curiosity, could serve as a practical resource. Experimental verification of related phenomena was recognized by the 2022 Nobel Prize in Physics.

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.

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 catalyze a generation of physicists and computer scientists to work across disciplinary boundaries.

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. Many of today’s ambitious efforts to build large-scale quantum systems trace their conceptual foundations to the theoretical breakthroughs pioneered by Bennett and Brassard.

Looking ahead, the next chapter of quantum information science includes the pursuit of fault-tolerant quantum computers, new quantum algorithms, and long-distance quantum communication enabled by satellites and quantum repeaters. Teleportation, entanglement swapping, and distillation—once abstract theoretical ideas—are now central components of practical quantum engineering.

Biographical Background

Charles H. Bennett is an American physicist whose research has shaped the foundations of quantum information science, quantum cryptography, and quantum teleportation, and who has played a central role in establishing quantum information science as a rigorous scientific discipline. After earning his Bachelor’s degree from Brandeis University and his PhD from Harvard University, Bennett joined IBM Research in 1973 (and still works there today), where he has spent his career exploring connections between physics (especially thermodynamics and quantum mechanics) and computer science (cryptography, computability, computational complexity, and information theory), to advance the theoretical and practical understanding of computation and quantum mechanics. He is a recipient of several prominent awards including the Wolf Prize in Physics, the Micius Quantum Prize, the BBVA Foundation Frontiers of Knowledge Award in Basic Sciences, and the Breakthrough Prize in Fundamental Physics. He is also a Member of the US National Academy of Sciences and a Foreign Member of the Royal Society.

Gilles Brassard is a Canadian computer scientist widely recognized as the first in the world to have delved into the uncharted territory of quantum information science. He earned his Bachelor’s and Master’s degrees from the Université de Montréal, and his PhD in theoretical computer science from Cornell University in 1979 under the direction of 1986 Turing Award laureate John E. Hopcroft. He joined the faculty of the Université de Montréal shortly thereafter and was Canada Research Chair in Quantum Information Science from 2001 to 2021. An Officer of the Order of Canada and of the Ordre national du Québec, Brassard has received numerous honors including the Wolf Prize in Physics, the Micius Quantum Prize, the BBVA Foundation Frontiers of Knowledge Award in Basic Sciences, and the Breakthrough Prize in Fundamental Physics. He is a Fellow of the Royal Society and an International Member of the U.S. National Academy of Sciences.