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 of these 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) than consumed input bits (953,301,640), which is 5 orders of magnitude more efficient than our previous work [arXiv:1812.07786]. The experiment ran for 91.0 hours, creating randomness at an average rate of 3606 bits/s with a soundness error bounded by 5.7×10−7 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 protocols may one day enable high-quality sources of private randomness as the device footprint shrinks.

1 aShalm, Lynden, K.1 aZhang, Yanbao1 aBienfang, Joshua, C.1 aSchlager, Collin1 aStevens, Martin, J.1 aMazurek, Michael, D.1 aAbellĂˇn, Carlos1 aAmaya, Waldimar1 aMitchell, Morgan, W.1 aAlhejji, Mohammad, A.1 aFu, Honghao1 aOrnstein, Joel1 aMirin, Richard, P.1 aNam, Sae, Woo1 aKnill, Emanuel uhttps://arxiv.org/abs/1912.11158