Relativistic position verification with coherent states

A secure approach to determining the position of an entity can enable schemes such as position-based authorization for transactions and tracking of high-value targets. However, classical methods are incapable of providing secure position verification in the untrusted-prover case, meaning that a prover can mislead verifiers about its actual position. Here we propose and experimentally realize a secure position verification protocol that combines quantum optics and relativity within an information-theoretic framework. Using phase-randomized weak coherent states, two verifiers separated by 2 km securely verify the prover’s position with an accuracy better than 75 m. These results establish secure position-based authentication as a practical possibility, paving the way for applications in financial transactions, disaster response and authenticated secure communications.