Researchers at ETH Zurich have, for the first time, generated certifiably perfect random numbers using a quantum experiment that could underpin future secure encryption methods. The team achieved this feat not by creating randomness from scratch, but by amplifying existing imperfect randomness using entangled superconducting qubits and a sophisticated “Bell-test” across a 30-meter link connecting two quantum chips. “It may seem strange, but it is almost impossible to create a perfect coin or a perfect die,” explains Renato Renner, highlighting the challenge of true randomness; even the most advanced generators typically exhibit slight biases. In a demonstration of the technology, a sheep image encrypted with ordinary randomness remained partially visible, while the same image using the ETH Zurich’s certified perfect randomness dissolved entirely into noise. This advancement, recently published in Nature, represents a milestone in the pursuit of digital security.
Entangled Qubits and Bell-Tests Enable Randomness Amplification
Quantum entanglement and rigorous Bell-tests are now being harnessed to overcome a fundamental limitation in digital security: the generation of truly random numbers. While conventional random number generators invariably exhibit subtle biases, researchers at ETH Zurich have demonstrated a method to amplify existing imperfect randomness into certifiably perfect randomness, a feat detailed in a recent publication in Nature. This advancement relies not on creating randomness from scratch, but on refining it through quantum mechanical principles. The team, led by Renato Renner and Andreas Wallraff, constructed a complex experimental setup featuring two superconducting qubits connected by a 30-meter-long, cryogenically cooled tube. These qubits, leveraging the phenomenon of quantum entanglement, allow for correlated measurements; a measurement on one qubit instantaneously influences the state of the other, even at a distance.
The 30-meter separation is crucial, ensuring no information can be exchanged between qubits at the speed of light, preserving the integrity of the randomness. This setup facilitated an improved “Bell-Test,” a method for verifying the entanglement, coupled with a novel algorithm to amplify the randomness derived from an initially imperfect generator. “This was made possible by an improved so-called Bell-Test with simultaneously high quality and high data rate,” explains Wallraff. The resulting sequence of “0”s and “1”s is demonstrably perfect, a level of randomness the researchers claim “will remain perfectly random for all eternity – no matter what analytical methods are used to assess their randomness.” This technology promises a physically certified source of randomness, potentially becoming as foundational for digital security as atomic clocks are for accurate timekeeping.
Imperfect Randomness Corrected via Quantum Measurement
The pursuit of truly random numbers has long been a challenge, as even sophisticated algorithms and physical processes yield sequences with subtle, exploitable biases; these imperfections, while often negligible for everyday tasks, pose significant risks to cryptographic security. Researchers are now moving beyond simply generating randomness to actively correcting it, a strategy recently demonstrated by a team at ETH Zurich. Their approach doesn’t rely on pristine initial conditions, but instead amplifies existing, imperfect randomness using principles of quantum mechanics. Central to this advancement is a 30-meter link connecting two superconducting chips cooled to near absolute zero. This entanglement, combined with a refined “Bell-Test,” enables the amplification of randomness. The team’s setup ensures that no information can be exchanged between the qubits during measurement, preventing any disturbance to the randomness. The process involves intentionally introducing imperfect randomness into the measurement basis of the qubits, then employing a specialized algorithm to amplify the resulting signal. “The resulting sequence of zeros and ones is now really perfectly random, and we can even certify that,” Renner states.
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.
Certified Perfect Randomness for Secure Digital Applications
This advancement relies on harnessing the principles of quantum entanglement between superconducting qubits housed on separate chips. A key element of the experiment is a 30-meter-long, cryogenically cooled link connecting the two quantum chips, facilitating the exchange of microwave photons and establishing entanglement. This physical separation is not merely a technical detail; it’s crucial to prevent information exchange between the qubits during measurement, which would undermine the randomness. The team employed an improved “Bell-Test” to achieve high-quality, high-data-rate measurements, allowing them to amplify the randomness of initial results using a specialized algorithm. This certified randomness could significantly enhance digital security protocols.
Even modern random number generators, which are based on quantum mechanical effects like the reflection of photons from beam splitters, are not entirely immune to such a systematic error or ‘bias’”, adds Wallraff.
