Researchers at ETH Zurich have developed a method to generate what they describe as “perfect” random numbers using quantum physics, a breakthrough that could strengthen encryption systems and digital security tools.
The team created the system using two superconducting quantum chips connected by a 30-meter-long cooled tube. The setup allowed the researchers to generate certified random numbers by exploiting quantum entanglement, where measurements on one quantum bit influence another instantly across distance.
Random numbers are critical for technologies such as encryption, digital identities, lotteries, blockchain systems, and secure communications. However, even modern random number generators can contain tiny biases, where some numbers appear slightly more often than others.
For most applications, those imperfections are negligible. But in cryptography, even the smallest deviation can create vulnerabilities that attackers may exploit.
Chasing perfect randomness
“It may seem strange, but it is almost impossible to create a perfect coin or a perfect die”, said Renato Renner, professor in the Department of Physics at ETH Zurich.
“No matter how symmetric and smooth a die is made, after a roll one of its six faces will always point upwards slightly more often.”
The researchers said even quantum random number generators based on photons and beam splitters are not fully free from systematic errors or bias. To address this, the ETH Zurich team developed a process called “randomness amplification,” which transforms imperfect randomness into certified perfect randomness.
The experiment relied on a Bell test, a well-known method in quantum physics used to verify entanglement between particles. Researchers used two qubits cooled close to absolute zero and linked through microwave photons traveling between the chips.
“This was made possible by an improved so-called Bell-Test with simultaneously high quality and high data rate”, said Andreas Wallraff, another lead researcher on the project.
The 30-meter separation between the qubits played a critical role. According to the researchers, the distance ensured that no information could travel between the chips during measurements, even at the speed of light, preventing interference with the randomness.
Quantum chips seal deal
The team intentionally selected measurement settings using an imperfect random number generator. They then applied a specialized algorithm to amplify the randomness of the resulting measurements.
“The resulting sequence of zeros and ones is now really perfectly random, and we can even certify that”, said Renner.
He compared the achievement to crossing a major technological threshold. “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.”
Researchers believe the technology could eventually serve as a trusted source of randomness for secure digital systems, much like atomic clocks provide certified timekeeping standards today.
The work may also support future quantum-secure communication networks, where strong encryption depends heavily on high-quality random numbers.
The study was published in the journal Nature.