Alum Gilles Brassard receives Turing Award, highest CS honor

Gilles Brassard, Ph.D. '79, has received the 2025 A.M. Turing Award from the Association for Computing Machinery (ACM), jointly with Charles Bennett, for founding the field of quantum information science and for new encryption technology for secure communication and computing.

Commonly referred to as the "Nobel Prize of computing," the Turing Award comes with a $1 million prize. It is named for Alan M. Turing, the British mathematician and parent of theoretical computer science.

Brassard is a Canadian computer scientist and faculty member at the University of Montreal, where he earned his bachelor's and master's degrees. At the age of 24, he received his Ph.D. in theoretical computer science from Cornell, working with John E. Hopcroft, professor emeritus of computer science and a 1986 Turing Award recipient.

Brassard met Bennett, a physicist at IBM Research, in 1979 while the two were swimming off the coast of Puerto Rico. Brassard was taking a break from a conference on theoretical computing, where he was presenting his graduate work on the mathematical foundations of cryptography. Bennett swam up to him and proposed an idea for a bank note that couldn't be counterfeited based on principles of quantum mechanics - the behavior of light and matter, often at the scale of atoms and subatomic particles.

Their collaboration led to the development of quantum cryptography - the application of quantum mechanics to encrypt, transmit and decode information securely. Their system, named BB84, used particles of light to make encryption keys that could lock and unlock digital data. Thanks to the laws of quantum mechanics, anyone who tried to hack the key would leave telltale traces the information was compromised.

"Gilles Brassard's BB84 protocol laid the foundation for quantum information science and reshaped the future of secure communication," said Lorenzo Alvisi, the Tisch University Professor in Computer Science and chair of the Department of Computer Science in the Cornell Ann S. Bowers College of Computing and Information Science. "We are proud to count him among our Cornell graduates, whose achievements continue to amplify the department's legacy of groundbreaking theoretical computer science - a tradition exemplified by his adviser, John Hopcroft."

Quantum cryptography is emerging as an important method to ensure the security of digital communication. Newer versions of BB84 have been deployed in quantum communication networks, through both landlines and satellites.

In later work, Brassard and Bennett demonstrated quantum teleportation, the idea that quantum information could be transmitted between distant locations using quantum entanglement, a phenomenon where the quantum state of two particles remains connected, even when they are too far apart to influence each other. Advances in quantum entanglement may one day lead to the growth of quantum networks and even a quantum internet that will transmit quantum information securely worldwide.

"Bennett and Brassard fundamentally changed our understanding of information itself," Yannis Ioannidis, president of the ACM, said in a statement. "Their insights expanded the boundaries of computing and set in motion decades of discovery across disciplines. The global momentum behind quantum technologies today underscores the enduring importance of their contributions."

In addition to Brassard and Hopcroft, Juris Hartmanis, the founding chair of Cornell's Department of Computer Science, received the Turing Award in 1993 for foundational work in the field of computational complexity.

Patricia Waldron is a writer for the Cornell Ann S. Bowers College of Computing and Information Science.