Trustworthy public randomness from loophole-free Bell tests

Some digital security applications, like the choosing of passwords, require private generation unpredictable symbols. Other applications, like lotteries, require the public generation of unpredictable symbols. Lotteries illustrate well the challenges of public randomness generation: how does the chooser convince the public that the numbers were really random? Can the public in some way verify that they were random? Applications requiring public randomness are found in business contracts, elections, and fair distribution of indivisible resources. Kavuri et al [1] reports the first publicly verifiable randomness generation, using a combination of quantum physics and blockchain-like public data structures. A loophole-free Bell test (recognized with the Physics Nobel Prize in 2022) is a quantum physics experiment in which entangled particles are measured in spatially-separated locations, to give results whose unpredictability is guaranteed by the impossibility of faster-than-light communication [2]. The good functioning of the experiment can be verified by analysis of the results obtained, while also extracting a small number of purely random symbols from the imperfectly random experimental results. Crucially, this verification and extraction can be done not just by the experimenters, but also by third parties; this allows the public to verify that the experiment was working as required. The protocol demonstrated here uses two third parties; one to perform the verification and extraction, and the other to say precisely how these analyses should be performed. All the steps are published in a blockchain-like public ledger, an intertwined hash chain, allowing anyone to verify that the process was done fairly. A public service, the randomness beacon offers continuously-generated random bits to whoever needs them. It is the first security benefit obtained by combining quantum 2.0 and web3 technologies.