ETH Zurich Physicists Generate Certifiably Perfect Randomness via Quantum Entanglement

A team at ETH Zurich has produced a stream of bits that can be mathematically proven to be perfectly unpredictable. The result, published in *Nature*, demonstrates randomness that remains certified even against any future analytical method.

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True randomness is essential for cryptography, yet deterministic devices—including computers and even coin flips—are, in principle, predictable. Prior quantum random-number generators offered high entropy but relied on trusted hardware and assumed flawless seeds. ETH Zurich’s approach leverages randomness amplification: starting from an imperfect source and using quantum entanglement to generate provably perfect randomness, a task shown impossible by purely classical means.

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The researchers entangled two superconducting qubits placed 30 m (98 ft) apart and cooled them near absolute zero. Over roughly nine hours they performed more than one billion Bell-test trials, obtaining correlations that cannot be explained by hidden classical rules. The distance ensured that no signal traveling at light speed could influence the measurements, guaranteeing device-independent randomness.

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Randomness underlies password generation, authentication codes, and encryption keys. Recent flaws such as the 2024 PuTTY vulnerability and the 2025 AMD Zen 5 RDSEED bug illustrate how predictable random numbers can compromise security. The ETH Zurich system offers a hardware-agnostic source of randomness, potentially serving as a physical standard comparable to atomic clocks for timekeeping.

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The ETH Zurich team reports that their experiment achieves randomness amplification, a capability unattainable by classical methods. By converting an imperfect seed into a stream of bits certified as perfectly random, they claim the result is device-independent: the observed quantum behavior alone guarantees unpredictability, irrespective of hardware trust. The authors emphasize that the technique could become a universal benchmark for randomness generation.

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• “The resulting sequence of zeros and ones is now really perfectly random, and we can even certify that,” — Renato Renner, Physicist, ETH Zurich

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• “Any conventional electronic device, like a phone or a computer, is completely deterministic," Renner told Adam Kovac at Scientific American, "so it's actually very difficult for a computer or any other electronic device to generate a random value.” — Renato Renner, speaking to Adam Kovac

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• “randomness amplification has been proven to be impossible by purely classical means.” — ETH Zurich research paper

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• “The technical improvements allowed us, for the first time, to create random numbers that will remain perfectly random for all eternity – no matter what analytical methods are used to assess their randomness,” — Renato Renner

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The researchers plan to scale the setup into a practical randomness service for cryptographic protocols and scientific measurements. Future work will focus on integrating the technology into deployable devices and establishing it as a benchmark for certified randomness.

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