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Professor Emeritus Horace Yuen Passes Away

Yuen was a leader in physics- and mathematics-based quantum and classical cryptography

Horace YuenHorace Yuen, professor emeritus of electrical and computer engineering at Northwestern Engineering, passed away on January 16, 2025. He will be remembered as a leading scholar, deep thinker, and pioneer in the field of physics- and mathematics-based quantum and classical cryptography.

During his 41-year career at Northwestern, during which he was also a professor of physics and astronomy in the Weinberg College of Arts and Sciences, Yuen was a leader in theoretical quantum optics and communication, the foundations of quantum physics, cryptographic protocols, information theory, and new quantum devices.

“Horace was a true scholar who made deep theoretical contributions to complex problems,” said Randall Berry, John A. Dever Chair of Electrical and Computer Engineering at the McCormick School of Engineering. “He will be missed.”

Among his foundational research accomplishments in the field of quantum cryptography, Yuen received a patent for developing an “Ultra-Secure, Ultra-Efficient Cryptographic System.” The system extends a short, shared secret key into a long, extended key which selects a quantum or classical signal set. The security level objective is achieved by adjusting the strength of each signal in the set according to the total number of signal sets.

Yuen also developed a cryptographic technique called the decoy bits method (DBM) with near ideal information-theoretic security in both quantum and classical key generation and data encryption. The DBM encryption system inserts random bits into a data sequence and subsequently discards the decoy bits during the decryption process.

In 2020, Yuen’s paper, “Two-photon Coherent States of the Radiation Field,” was selected for inclusion in Physical Review A's 50th Anniversary Milestone Collection of notable papers in the fields of atomic, molecular, and optical physics and quantum information. Yuen’s research into two-photon coherent state, or squeezed state of light, was foundational to potential applications in precision measurement and optical communications. Squeezed light is now routinely used to enhance the sensitivity of gravitational wave detectors.

Yuen retired from Northwestern in 2021.

Yuen, who earned his PhD in electrical engineering and his master’s in electrical engineering from MIT, received several honors throughout his career, including being named among the inaugural recipients of the biennial International Quantum Award for “outstanding achievements in quantum science research.” In 2004, the American Physical Society Council elected Yuen as a Division of Laser Science Fellow “for seminal contributions to the theory of quantum communications and quantum measurements.”

In 2008, Yuen received the Quantum Electronics Award from the Institute of Electrical and Electronics Engineers “for pioneering and seminal contributions to the theory of the generation, detection, and applications of novel states of light.”

A funeral service will be held at 2 p.m. on January 22 at the Ryan-Parke Funeral Home, 120 South Northwest Highway in Park Ridge, Illinois.