The Laboratory and Princeton University have successfully completed a novel experiment for a system that, when fully developed, could prove useful in the verification of declared warheads in support of future disarmament agreements. The experiment translated a mathematical concept called “zero-knowledge proof” that is employed in cryptography — the science of disguising information — into a physical system. The aim of the system that PPPL and Princeton University are developing is to determine, without exposing classified information, whether objects to be dismantled are true nuclear warheads.

“This is the first experimental demonstration of a physical zero-knowledge proof,” said Sébastien Philippe, a graduate student in the Department of Mechanical and Aerospace Engineering at Princeton and lead author of a Nature Communications paper about the research.

The experiment beamed high-energy neutrons into a set of 2-inch steel and aluminum cubes arranged first in a “true” pattern and then in several “false” patterns. The neutrons passed through to bubble detectors that counted the number that reached them through the different arrangements of cubes. By comparing the numbers to those previously designated for the “true” arrangement, researchers were able to distinguish it from “false” arrangements.

In an actual inspection, such as one involving a real nuclear warhead, the proposition is that no information would be exposed or shared in the process – so long as the owner of the warheads presented only true items. This would be accomplished, as demonstrated in the experiment, by the owner of the weapons pre-loading the detectors with a “negative” of the real image, so the summed counts would show a uniform signal.

The research marked the initial physical step toward a technique that could prove useful in future disarmament talks pending further development, testing and evaluation. While important questions remain, the method might have potential application for verifying that nuclear warheads presented for disarmament were in fact true ones.

Co-authors of the Nature Communications piece were Robert Goldston, a Princeton professor of astrophysical sciences, fusion scientist and former director of PPPL; Alex Glaser, associate professor in Princeton’s Woodrow Wilson School of Public and International Affairs and the Department of Mechanical and Aerospace Engineering; and Francesco d’Errico, senior research scientist at the Yale School of Medicine and professor at the University of Pisa, Italy.