# Charles H. Bennett

## contact information

Thomas J. Watson Research Center, Yorktown Heights, NY USA

+19142245225

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BIOGRAPHY of CHARLES H. BENNETT Dec 2021.

Born in 1943 to two music teachers, Charles H. Bennett always wanted to be a scientist. After undergraduate work in organic chemistry he got his doctorate in chemical physics and began a postdoc in computational statistical physics at Argonne Laboratories. There he heard a talk by IBM's Rolf Landauer connecting energy dissipation by computers to to their performing logically irreversible operations such as erasure, and began thinking about how to avoid such operations. He continued this work at IBM Research, which has been his home institution since 1972. In 1973, building on Landauer's work, he showed that general-purpose computation can indeed be performed by a logically and thermodynamically reversible apparatus, such as a chemical Turing machine. In 1982 he proposed the now commonly accepted resolution of the Maxwell's Demon paradox, attributing its inability to break the second law to the thermodynamic cost of destroying, rather than acquiring, information. In 1979, he studied the thermodynamics of error-correction in a model of RNA transcription with and without proofreading, and in 1985 with IBM's Geoff Grinstein, he showed how dissipation qualitatively stabilizes long-term memory in locally interacting noisy Ising-like systems, which under equilibrium conditions could be at best metastable with respect to symmetry-breaking perturbations.

Beginning in the 1980's Bennett and collaborators helped establish quantum information as the natural arena within which to formalize notions of communication and computation, leaving the classical theories of Turing and Shannon as interesting and useful special cases. In 1984, with Gilles Brassard of the University of Montréal, building on the seminal insights of Stephen Wiesner, he developed a practical system of quantum cryptography, allowing secure communication between parties who share no secret information initially, with security based on the laws of quantum mechnaics instead of usual computational assumptions such as the difficulty of factoring, and with the help of their students built a working demonstration of it in 1989. In 1993 Bennett and Brassard, in collaboration with Claude Crépeau, Richard Jozsa, Asher Peres, and William Wootters, discovered "quantum teleportation," an effect in which the complete information in an unknown quantum state is decomposed into purely classical information and purely non-classical entanglement, sent through two separate channels, and later reassembled in a new location to produce an exact replica of the original quantum state that was destroyed in the sending process. This and other protocols for entanglement-assisted communications showed that entanglement is a useful, quantifiable resource despite having no communications ability by itself. In 1995-7, working with Smolin, Wootters, David DiVincenzo, and other collaborators, he devised several techniques for faithful transmission of classical and quantum information through noisy channels. With Devetak, Harrow, Shor, Smolin, Thapliyal and Winter, in 2002 and 2014, he proved the classical and quantum reverse Shannon theorems, showing that all classical (resp. quantum) channels of equal capacity (resp. entanglement-assisted capacity) can efficiently simulate another in the presence of shared randomness (resp. enganglement).

In the field of algorithmic information theory, which develops concepts of information and randomness in terms of the input/output relation of universal computers, Bennett introduced "logical depth" to formalize the kind of complexity that is absent from subjectively trivial configurations like a gas or perfect crystal but increases during what would informally be called self-organization. Defined as the minimal time required for a univeral computer to compute a configuration from a near-incompressible input, it represents the minimal amount of compution needed to simulate its plausible ontogeny.

In 2014 and 2018, with his former postdoc Jess Riedel and cosmologist Andreas Albrecht, Bennett orgnized workshops at IBM and the Niels Bohr Institute exploring how tools of quantum and algoritmic information can be applied to vexing problems in cosmology, such as the origin of classical phenomenology and the Boltzmann brain problem.

Bennett has lectured to lay audiences around the world attempting with some success to show that despite quantum mechanics' fearsome reputation, and the fact that Einstein didn't like it, the quantum nature of information is an important but non-obvious feature of our universe that ordinary people can comprehend the gist of, as they do, say, of black holes.

Bennett is an IBM Fellow, a Fellow of the American Physical Society, and a member of the National Academy of Sciences. Widowed and remarried, he has a large family, including seven grandchildren of his late wife. His main hobbies are photography and music.