⚛️ Physicists create 'perfect randomness'

Even the most sophisticated classical random number generators have minute biases that make their sequences predictable over the long term. In cryptography, this flaw could be exploited by attackers. Researchers at ETH Zurich have now made a decisive breakthrough by producing what they call 'perfect randomness', leveraging the counterintuitive properties of quantum physics.

The experimental setup relies on two superconducting chips cooled to temperatures near absolute zero. Each chip constitutes a qubit, the quantum equivalent of a classical bit. Connected by a tube about 100 feet (30 meters) long, also cooled, these chips can exchange microwave photons in an entangled state. In this state, measuring one qubit instantly influences the other, regardless of the distance between them.


To ensure the integrity of the process, the researchers placed the qubits nearly 100 feet (30 meters) apart. This way, even a signal traveling at the speed of light could not connect the two qubits during measurement. This spatial separation prevents any unwanted communication that could distort the randomness—a simple but effective technique to preserve the purity of entanglement.

How to 'purify' randomness?

The protocol begins by using an imperfect random number generator (the classical, biased randomness of a computer) to choose the measurement basis for the qubits.

Suppose the classical computer gives a flawed starting impulse, like a biased coin that would land 60% on Heads and 40% on Tails. It is this biased signal that the researchers send into the quantum system.

That is where the magic of entanglement kicks in. Before being measured, the entangled qubits exist in a fundamentally superposed state: the result is not merely hidden—it does not yet exist and is strictly impossible to know in advance. The impulse from the computer (the 60-40 fake randomness) simply triggers the measurement of these qubits. At that precise moment, nature is forced to make a pure choice, restoring a perfect and totally unpredictable 50-50.

The core idea is that the quantum system acts as a 'purity filter': it uses a biased input to force a quantum reaction whose final randomness is certified by the laws of physics, not merely assumed through classical statistical tests. Quantum physics mathematically guarantees that the final result (0 or 1) is completely inviolable, even for the researchers who built the machine.

Far-reaching implications

Renato Renner, co-author of the study published in Nature, explains that this method significantly reduces computational cost. "Our approach doesn't really require computation," he said, "because all the randomness is generated by the measurement of the qubits. The computational cost is negligible compared to that of pseudo-random generators."

The practical implications are considerable. Researchers compare this breakthrough to that of the atomic clock for time measurement: a reliable physical standard that other systems can rely on. Potential applications include message encryption, digital identities, lotteries, and blockchain operations. Renner notes that their experiment would be particularly useful in network architectures where each node can access a server implementing this perfect random generator.