ETH Zurich researchers say they have generated certified “perfect randomness” for the first time by using a quantum Bell-test setup with two entangled superconducting chips connected by a 30-meter cooled link. “In the long term, this work could play a similar role in digital security as atomic clocks do for timekeeping: a physically certified source of randomness that other systems can rely on,” reports Phys.org. “Possible applications range from the encryption of sensitive communications and digital identities to public randomness services for lotteries and blockchain applications.” From the report: They call their method randomness amplification. “This was made possible by an improved so-called Bell-Test with simultaneously high quality and high data rate,” says [Renato Renner and Andreas Wallraff]. He and his coworkers use a complex setup that consists of two superconducting chips, which they cool down to very low temperatures close to absolute zero. Each chip represents a quantum bit or qubit, which can take on the states “0” or “1” or any arbitrary superposition of these states. A 30-meter-long tube, which is also cooled down, connects the two chips.
Microwave photons can fly back and forth between them, thus creating quantum mechanical entanglement. This means that a quantum measurement on one qubit, which randomly yields the values “0” or “1,” influences automatically and at a distance whether “0” or “1” is measured on the second qubit. The separation of 30 meters ensures that, during the measurement, even at the speed of light, no information can be exchanged between the qubits. This would disturb the perfect randomness.
Wallraff and his team made the choice of the exact type of measurement (or “measurement basis” in technical jargon) on the two qubits depending on an imperfect random number generator. Renner’s coworkers could then amplify the randomness of the measurement results further using a special algorithm. “The resulting sequence of zeros and ones is now really perfectly random, and we can even certify that,” says Renner. He likens this result to crossing a ridge: “The technical improvements allowed us, for the first time, to create random numbers that will remain perfectly random for all eternityâ”no matter what analytical methods are used to assess their randomness.”
The findings have been published in the journal Nature.