Środowiskowe Seminarium z Informacji i Technologii Kwantowych

We use the entanglement sampling techniques developed by Dupuis, Fawziand Wehner to find a lower bound on the entanglement needed by acoalition of cheater attacking the quantum position verificationprotocol using the four BB84 states in the scenario where the cheatershave no access to a quantum channel but share a (possibly mixed)entangled state Φ. For a protocol using n qubits, a necessary conditionfor cheating is that the max- relative entropy of entanglementEmax(Φ)≥n−O(logn). This improves previously known best lower boundby a factor ∼4, and it is essentially tight, since this protocol isvulnerable to a teleportation based attack using n−O(1) ebits ofentanglement.