Loss-Tolerant Quantum Position Verification for Metropolitan Area Networks

AI summary

Overview

Research area: Quantum position verification (QPV), quantum cryptography, and metropolitan-scale quantum networks.
Technical level: Intermediate.
Scope: This paper introduces LT-QPV, a loss-tolerant quantum position verification protocol, proves finite-size security against quantum polynomial-time adversaries in the quantum random oracle model, and demonstrates position certification over approximately 60 m using commercial off-the-shelf hardware.

What This Paper Is About

Digital signatures do not prove where a signing event occurred, and purely classical position-verification schemes can be spoofed by colluding adversaries. Quantum position verification uses the no-cloning theorem and the no-signaling principle to certify a party’s spacetime location, but channel loss has made prior protocols difficult to deploy at metropolitan scales. This paper proposes and experimentally demonstrates a loss-tolerant QPV protocol whose security is independent of channel loss, using a single quantum verifier node alongside classical infrastructure.

Key Contributions

1. A loss-tolerant QPV protocol (LT-QPV): The prover prepares a Bell state and sends one qubit to the quantum verifier, making the protocol a source-independent version of an (f)-measure QPV protocol. Security depends only on local losses at the prover, and verifier no-detection rounds can be safely discarded.
2. Finite-size security proof in the quantum random oracle model: The authors prove security against quantum polynomial-time entangled adversaries for both independent and identically distributed (i.i.d.) attacks and general coherent attacks under sequential repetition. The protocol is shown to be (\varepsilon_{\mathrm{sou}})-sound and (\varepsilon_{\mathrm{com}})-complete, with no assumptions on the prover’s source.
3. Experimental demonstration with commercial hardware: Using a warm rubidium entanglement source, 16 measurement bases, FPGAs, and Pockels cells at a 200 kHz repetition rate, the system certifies the prover’s position in under 22 minutes of net data collection time against a restricted adversary.
4. Metropolitan deployment and scaling analysis: The architecture requires only one quantum verifier node plus classical verifiers, and scaling

Authors’ abstract

A spacetime seal, a cryptographic guarantee that a digital event has occurred at an approved location and time, can augment a digital signature with location attestation for legal, financial, and regulatory use cases. In adversarial settings any purely classical realization of such a seal can be spoofed. Quantum position verification (QPV) offers a physics-based solution, exploiting the no-cloning theorem and the no-signaling principle to certify a party's spacetime coordinates. While the feasibility of QPV has been recently shown via entanglement- and coherent light-based protocols, achieving loss tolerance for these schemes substantially increases implementation complexity at metropolitan scales. Here, we introduce and experimentally demonstrate a loss-tolerant QPV (LT-QPV) protocol whose security is independent of channel loss. We prove finite-size security against quantum polynomial-time entangled adversaries in the quantum random oracle model instantiated with cryptographically secure hash functions. Implemented entirely with commercial off-the-shelf components, our system certifies position within 22 minutes of net data collection time against a restricted adversary, with a clear path to real-time certification (<1s) with upgraded hardware. Our architecture, requiring only a single quantum verifier node alongside classical infrastructure, is naturally compatible with metropolitan-area quantum networks, establishing the foundations for scalable, physics-backed spacetime certification as a deployable service.