Richard P. Mirin

With the growing availability of experimental loophole-free Bell tests, it has become possible to implement a new class of device-independent random number generators whose output can be certified to be uniformly random without requiring a detailed model of the quantum devices used. However, all previous experiments require many input bits in order to certify a small number of output bits, and it is an outstanding challenge to develop a system that generates more randomness than is used. Here, we devise a device-independent spot-checking protocol which uses only uniform bits as input. Implemented with a photonic loophole-free Bell test, we can produce 24% more certified output bits (1,181,264,237 bits) than consumed input bits (953,301,640 bits), which is 5 orders of magnitude more efficient than our previous work [Phys. Rev. Lett. 124, 010505 (2020)]. The experiment ran for 91.0 hours, creating randomness at an average rate of 3,606 bits/second with a soundness error bounded by 5.7e-7 in the presence of classical side information. Our system will allow for greater trust in public sources of randomness, such as randomness beacons, and the protocol may one day enable high-quality sources of private randomness as the device footprint shrinks.