Continuous-variable Quantum Position Verification secure against entangled attackers

TL;DR

This paper demonstrates that a continuous-variable quantum position verification protocol using coherent states remains secure against entangled attackers when additional classical information is included, even under realistic noise and loss conditions.

Contribution

It extends security proofs of CV-QPV protocols to scenarios with added classical information and realistic noise, showing robustness against entangled attacks.

Findings

Security holds with added classical info of size n

Protocol remains secure under certain noise and attenuation

Security against CV-entangled attackers with linear photon number cutoff

Abstract

Motivated by the fact that coherent states may offer practical advantages it was recently shown that a continuous-variable (CV) quantum position verification (QPV) protocol using coherent states could be securely implemented if and only if attackers do not pre-share any entanglement. In the discrete-variable (DV) analogue of that protocol it was shown that modifying how the classical input information is sent from the verifiers to the prover leads to a favourable scaling in the resource requirements for a quantum attack. In this work, we show that similar conclusions can be drawn for CV-QPV. By adding extra classical information of size $n$ to a CV-QPV protocol, we show that the protocol, which uses a coherent state and classical information, remains secure, even if the quantum information travels arbitrarily slow, against attackers who pre-share CV (entangled) states with a linear (in $n$) cutoff at the photon number. We show that the protocol remains secure for certain attenuation and excess noise.