Alexandra Popp

At its core quantum key distribution (QKD) offers information theoretical security based on the laws of physics. In deployments one has to take into account practical security and resilience. The latter includes the localization of a possible eavesdropper after an anomaly has been detected by the QKD system to avoid denial-of-service. In this work, we present a novel approach to eavesdropper localization inside a quantum channel based on opto-acoustic interaction. Employing localized stimulated Brillouin scattering, we are able to localize common eavesdropping approaches such as evanescent outcoupling as low as 1% of optical transmission power to the cm level. Furthermore we are capable to distinguish multiple nominally indistinguishable fibers from different manufacturers, paving the way for high security applications. Finally we show, that this approach surpasses traditional OTDR technology.