Device-Independent Quantum Position Verification

Remote, location-based authentication is fundamental to modern position, navigation, and timing systems, and plays a critical role in cryptography, security, and commerce. Classical protocols for this task are based on ranging techniques, in which trusted "verifiers" confirm that an untrusted "prover" is located in a target space-time region by timing signals to and from that region. However, this approach can always be spoofed by the presence of multiple colluding adversaries. Quantum position verification (QPV) protocols combine this technique with the no-cloning property of qubits, but current proposals are infeasible with existing hardware. Here, we demonstrate the first experimental implementation of QPV with a new protocol based on a loophole-free photonic Bell test. In this task, two verifiers are separated by 200 meters apart and run a protocol that an honest prover can pass with high probability, but adversaries outside a target region have a low probability of passing. The protocol is fully device-independent, making it immune to side-channel attacks and does not rely on assumptions about the devices involved. With this protocol, we demonstrate a 78% improvement in the three-dimensional localization performance of our quantum protocol compared to classical ranging.