certified randomness – A new Nature study describes a two-qubit system that generates randomness and verifies it through repeated Bell tests, aiming to prevent the subtle patterns that can undermine encryption. Researchers say the method can transform ordinary images into output tha
For people who rely on passwords, keys, and encrypted messages, “random enough” has never been a comforting promise. It has always been a hope. Because in the real world. randomness generated by conventional electronics can carry hidden imperfections—enough for attackers to look for patterns and chip away at secrecy.
Now. a quantum computing team is working from a different premise: randomness that isn’t just hard to guess. but certified to be genuinely unpredictable. In a paper published in Nature on Wednesday. Renato Renner. a physics professor at the Swiss Federal Institute of Technology Zurich (ETH Zurich) and a member of the research team. and his colleagues describe how a two-qubit system can generate true randomness—and verify that it isn’t being described by classical physics.
Renner’s starting point is blunt. Any conventional electronic device like a phone or a computer is deterministic. he says. which makes it very difficult for a computer to generate a random value. “It cannot just toss a coin because everything that goes on in the scale of the logic is basically completely predictable. ” he explains.
That predictability is the vulnerability modern encryption has to live with. Even when random number generators appear unpredictable at first glance. subtle imperfections can emerge—patterns that powerful computers can detect and that attackers can exploit by trying to predict parts of a password or a key.
Renner emphasizes why verification matters. “Unpredictability is very important because that’s what the adversary would do to attack it—to just try to predict parts of that password or even the full password or parts of the key,” he says.
The quantum approach begins with qubits, the basic components of information in a quantum computer. Unlike binary digits, qubits don’t exist in a simple “0” or “1.” They can occupy an infinite number of states until they’re measured, at which point they collapse into a single state.
In the study. the researchers entangled two qubits kept at temperatures near absolute zero at opposing ends of a 30-meter-long tube. When the two qubits were entangled, they shared the same positioning—so measuring both would produce the same output. The long tube wasn’t a cosmetic detail. Renner says it was necessary to ensure enough physical separation so outside variables couldn’t bias the results.
The team didn’t stop at generating randomness. They also designed a way to make sure it could not be explained by classical physics. “To really be sure that it’s not predictable, I need to have a process where I’m really sure that this process is not described by classical physics,” Renner says.
In one experiment. the system took a photograph of a sheep and ran its pixels through the quantum setup to translate them into randomness. The output looked like a mess of colors and splotches. According to the research, that transformation would be impossible to put back together—even using a quantum computer.
To further test the system, the researchers performed what’s known as a Bell test. This checks quantum behavior for any hints that the results might be affected by classical physics. Andreas Wallraff. Renner’s ETH Zurich colleague and a co-author of the study. says their setup could run many Bell tests with good quality and at a fast rate. “For our experiment. we ran about a billion and a half of these Bell tests to create certifiably random outcomes that then are used in an algorithm that Renato and his team had developed to create this certified randomness. ” Wallraff says.
Wallraff’s work with verification is also where the study’s significance sharpens. Renner says that while earlier experiments could generate randomness. the inclusion of a second qubit as a verification measure is new. That added step, he argues, enhances trust—an essential ingredient for solid encryption.
Even so, there’s a reality check built into the excitement. Commercially available quantum computers are still a long way off. But Renner points out that the implications of better randomness land right now. because cryptographic failures caused by imperfect randomness are already part of the internet’s history. He notes that there’s an entire Wikipedia page dedicated to hacks that were only possible because of imperfect cryptographic randomness.
“This is the problem we solve, which is a current problem, not only a problem in the post-quantum-cryptography era,” Renner says. “Of course, it will remain a problem.”
He also offers a broader view of the fight ahead: cryptography, he says, will always depend on good randomness, whether the threat comes from conventional adversaries or from future quantum ones.
The details in the Nature paper—two entangled qubits separated across a 30-meter tube. temperatures near absolute zero. and roughly a billion and a half Bell tests—are technical. But they circle one very human question: can the numbers we trust to protect our lives be trusted to be truly unpredictable?. In Renner’s system, the answer is designed to be not just convincing, but provable.
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