March 31, 2026

6 min read

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How physicists proved that quantum weirdness is a feature, not a bug

Charles H. Bennett and Gilles Brassard, winners of this year’s Turing Award, spent their lives touting the advantages of the quantum world

By Joseph Howlett edited by Clara Moskowitz

Charles H. Bennett (left) and Gilles Brassard (right) next to an exhibit depicting their BB84 protocol for quantum cryptography. Bennett and Brassard are the recipients of the 2026 A. M. Turing Award, an annual prize given by the Association for Computing Machinery.

Lise Raymond/Association for Computing Machinery

Most people find quantum mechanics complicated and difficult to grasp. Add information theory—the math behind computing—into the mix, and it’s a real headache.

But information theorists Charles H. Bennett and Gilles Brassard argue that quantum information is something we should all be getting used to. It’s simple and beautiful, they contend, and it won’t stay relegated to the remote world of the subatomic for long. Soon, for instance, it could disappear all the money in our bank accounts if we don’t act fast. That’s because quantum computers based on the theory could one day break the cryptography that secures our Internet and our financial system.

Bennett and Brassard recently received the A. M. Turing Award, which is bestowed annually by the Association for Computing Machinery. Named after the father of computing, Alan Turing, the award is often called the “Nobel Prize of Computing.” This year’s prize recognizes how the duo’s discoveries made quantum information relevant and inescapable. Brassard is a professor at the University of Montreal, and Bennett has worked at IBM for over 50 years.

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Before their work, even experts considered the quantum world separate from our own. Quantum theory’s math worked, but its logic was different, they thought. When it came to computing, the fact that the microscopic world is quantum was a troublesome headache, something that needed to be sorted out. Everything would work better, scientists believed, if they could safely ignore its twisty rules.

But rather than avoiding strange quantum phenomena such as superposition and entanglement, Bennett and Brassard embraced them. They found ways of inscribing uncrackable codes and transmitting microscopic states across huge distances that would be impossible with the classical computers Turing had envisioned.

Scientific American spoke with the computing pioneers about their achievements, their forewarnings and why we should all get comfortable with quantum.

[An edited transcript of the interview follows.]

How did you two start working together?

BRASSARD: The first time I heard about Charlie Bennett was by reading the November 1979 issue of Scientific American. A column printed one of Charlie’s manuscripts word for word. I read it on the plane to San Juan, Puerto Rico. The next day I was swimming, minding my own business, when this complete stranger comes up to me and starts telling me about physicist Stephen Wiesner and how to make bank notes that are impossible to counterfeit.

And that was Charlie!

BENNETT: People try to make money hard to counterfeit. But if you’re really good at it and work very hard and just sort of dissect it under a microscope, there’s no physical barrier to duplicating it. Wiesner realized you could take advantage of quantum mechanics to make money that’s physically impossible to counterfeit. Based on Wiesner’s ideas, Gilles and I realized it was possible for two people to establish an encryption key without anyone else being able to eavesdrop.

So how does this actually work?

BENNETT: So if “Alice” wants to send a secret key to “Bob,” she produces a train of photons, and the key is the polarizations of these photons. But anyone who wants to measure one of the photon’s polarizations has to pick one of two ways of measuring it—called rectilinear and diagonal. And if they choose the wrong one, they’ll get a random answer and spoil the photon’s original polarization.

But Bob has the same problem, right?

BENNETT: Indeed. Bob doesn’t know which polarizations Alice chose, so he guesses, randomly performing a rectilinear or diagonal measurement on each photon as it arrives.

BRASSARD: He spoils half of the states in the process—and he doesn’t even know which ones he spoiled. But then he tells Alice which measurements he chose—without telling her what results he got. And then Alice tells him which choices were correct.

They each throw