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I don't want to take anything away from Bennett and Brassard, but I'd like someone to spare a word for poor Stephen Wiesner, who invented the earliest quantum information-distribution protocols as far back as the 1960s and published them before Bennett and Brassard. He also invented Oblivious Transfer (OT) which is required for multi-party computation -- although his was a quantum protocol that demonstrated some of the ideas behind QKD, not the classical protocol we call OT today [1].* Weisner was an inspiration for Bennett and Brassard, who then realized more useful systems.
While obviously this takes nothing away from BB's many later contributions (and they have extensively credited him), it's just a reminder of the randomness that goes with scientific credit. Since my PhD thesis was on OT, I like to remind people of Wiesner. He deserves a lot more credit than he gets!
* I suppose if you're a real theoretician, since OT implies MPC and MPC implies all cryptography, then perhaps Wiesner's OT implies everything that BB did subsequently. I'm not sure any of that is true (and I've since checked with an LLM and there are some no-go theorems from the 1990s that block it, so that's super interesting.)
Don't forget about William Wootters, who also did significant work in the 1980s on quantum information. Most notably with Zurek, he proved the quantum no-cloning theorem in 1982. This result is at the same foundational level as energy conservation or constancy of light.
He was also on the Teleportation discovery in 1993.
If you enjoy reading about undervalued scientists, check out the life of Ernst Stückelberg, who missed out on 4 to 5 Nobel prizes because he mostly published in unknown journals. https://blogg.perostborn.com/2023/03/22/hes-not-so-easily-st...
As a young grad student, I remember going to a talk by Bennett where he explained how a Quantum Computer allows manipulation in a 2^N dimensional hilbert space, while the outputs measurements give you only N bits of information. The trick is to somehow encode the result in the final N bits.
I felt this was a much better layman explanation of what a quantum computer does than simply saying a quantum computer runs all possible paths in parallel.
> I felt this was a much better layman explanation of what a quantum computer does than simply saying a quantum computer runs all possible paths in parallel.
Relevant concerning your point:
> "The Talk"
That comic is great I understand qubits a bit better now: it has 4 degrees of freedom but can be mapped onto the 2d surface of a sphere because of normalization (circle rule) and global phase symmetry which each take away one of the four DOF
I need a longer think on the interference/computation connection though
Thanks for this! I guess i need to read up on Hilbert Space.
...and Shor's Algorithm
Don't let the terminology intimidate you. The interesting ideas in quantum computing are far more dependent upon a foundation in linear algebra rather than a foundation in mathematical analysis.
When I started out, I was under the assumption that I had to understand at least the undergraduate real analysis curriculum before I could grasp quantum algorithms. In reality, for the main QC algorithms you see discussed, you don't need to understand completeness; you can just treat a Hilbert space as a finite-dimensional vector space with a complex inner product.
For those unfamiliar with said concepts from linear algebra, there is a playlist [1] often recommended here which discusses them thoroughly.
[1] https://www.youtube.com/playlist?list=PLZHQObOWTQDPD3MizzM2x...
Yeah all the names and terminology really do make it seem harder than it is. Took me a long time and I’m still learning. 2d Hilbert space is same as 2d Euclidean space but each dimension has 2 degrees of freedom (real + imaginary). Might even think of it as 4d space, for vector imagining purposes, but that would probably be wrong and someone would call you out
* From the announcement [0]:
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.
* An accessible news excerpt via CNN science [1]
Years before emails, internet banking, cloud servers and cryptocurrency wallets, two scientists devised a way to keep secrets perfectly safe and indecipherable to eavesdropping outsiders.
Their 1984 work depended on the hidden, counterintuitive world of quantum physics, which governs the way the world works at the smallest, subatomic scale, rather than complex but theoretically breakable mathematical codes to secure data.
The insights of Charles Bennett, an American physicist who is a fellow at IBM Research, and Gilles Brassard, a Canadian computer scientist and professor at the University of Montreal, have since transformed cryptography and computing. The pair received the A.M. Turing Award on Wednesday for their groundbreaking work on quantum key cryptography.
[0] https://www.acm.org/media-center/2026/march/turing-award-202...
[1] https://edition.cnn.com/2026/03/18/science/quantum-key-crypt...
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> Bennett and Brassard, with Ethan Bernstein and Umesh Vazirani, showed that in black-box setting, quantum computers would require big-omega(sqrt(n)) queries to search n entries, matching Grover's algorithm. For some reason, the popular press rarely covers these results that limit the power of quantum computing.
This is mentioned almost as a footnote, but to (layman) me seems much more important than QKD, especially from a comp sci perspective instead of a physics perspective.
Worth noting that this is a bound on arbitrary search, but there exist some problems with structure (e.g. integer factorization) for which quantum algorithms are exponentially faster than known classical algorithms (a problem believed to be in NP and BQP but not P).
QKD can be sold today.
The quantum computers are not quite large enough to search at an `n` such that O(n)` is not viable but `O(sqrt(n))` is, that's where there's money to be made, especially if viability is defined by small time horizons. So it's a footnote for the future.
> QKD can be sold today.
It can, but it isn't largely because the classical solutions solve the problem better and you usually have to resort to classical solutions to solve MITM anyways afaik. However my point is less about practicality and more QKD seems more like a physics or engineering thing and not a computer science thing.
After all, this is supposed to be a computer science prize not a make money prize, so which is more sellable should be besides the point.
The math might be beautiful, but I'm very skeptical - practical - quantum computers will ever deliver their promise.
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Not sure what is going on in QC world; With this ACM prize it has become even more murky.
As Sabine Hossenfelder (Theoretical Physicist) points out, companies to do with QC are seeing a surge in investments and marketing. It is as if somebody knows something that the "common public" doesn't - https://www.youtube.com/watch?v=gBTS7JZTyZY
I don't know enough about the science/technology to form an opinion but have recently started down the path of trying to understand it - https://news.ycombinator.com/item?id=46599807
Check out Eric weinsteins latest theory about how frontier physics has moved “dark” (with a grain of salt, some of the other things he says might tempt you to discount him completely)
Forever is a long time, but I agree people that assert reality is the model are almost always incorrect eventually.
There is some interesting work being done, but it will never match the excessive hype. =3
"The Genius of Computing with Light"
That's 2 Turing award for the Université de Montréal in 6 years. Sadly, I never had those 2 teachers during my years there!
I did see Gilles' lunch talks though, it was really insightful!
Really curious, not a critique: apart from the idea of the possibility of intrusion detection due to the quantum nature of the communication link, what is special about the protocol that is mentioned?
Coincidentally, the same people also recently received the Science Fiction Award 2025!
Source?
I suspect the parent considers quantum computing science fiction.
Well deserved and much needed recognition in quantum key cryptography, for once not a single mention of "AI" anywhere.
Congratulations to Charles Bennett and Gilles Brassard.
old article but still relevant. some things don't change
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