Quantum Position Verification Achieves Secure Remote Localization with Loophole-Free Bell Tests

Researchers are tackling the fundamental challenge of securely pinpointing locations in a world where adversaries could possess complete knowledge of a target’s devices, rendering classical localisation impossible. Gautam A. Kavuri (University of Colorado, Boulder and National Institute of Standards and Technology), Yanbao Zhang (Oak Ridge National Laboratory), and Abigail R. Gookin (University of Colorado, Boulder) et al. present a groundbreaking protocol for device-independent position verification, crucially guaranteeing security without reliance on trusted hardware. Their experimental demonstration leverages loophole-free Bell tests across a network to certify the position of a remote party, even against adversaries with significant capabilities , achieving a one-dimensional localisation that is 2.47(2) times more precise than the best existing classical methods, and 4.53(5) times smaller when accounting for equivalent communication delays. This work represents a significant step towards anchoring digital security firmly in the laws of physics.

Quantum network verifies position

Scientists have demonstrated a groundbreaking protocol for device-independent quantum position verification, securing remote parties against location spoofing attacks. This research overcomes fundamental limitations of classical localization methods, which are inherently vulnerable to manipulation due to the potential for adversaries to possess complete knowledge of a party’s devices. The team achieved this breakthrough by leveraging loophole-free Bell tests across a Quantum network, guaranteeing security based solely on observed correlations, eliminating the need to trust vulnerable hardware. Experiments show the team implemented the protocol with two verifiers separated by 195.1(3) meters, performing 335 instances over two days, each consisting of a sequence of trials to verify position.
Security analysis reveals the protocol is robust against adversaries sharing limited prior entanglement, specifically bounded by an average robustness of 8×10−6 over the trials of a protocol instance. The research establishes that no adversary strategy without prior entanglement can outperform strategies based on three-party non-signaling correlations, deriving security from the fundamental principle of faster-than-light signaling impossibility. Conditional on successful protocol completion, scientists can confidently assert that a prover performed a quantum operation within a localized target spacetime region. While ideal localization could theoretically achieve arbitrary precision, practical limitations are imposed by communication and processing latencies.

Device-independent position verification via loophole-free Bell tests

Scientists engineered a novel protocol for device-independent position verification, circumventing limitations inherent in classical localization methods. The research team demonstrated security guarantees reliant solely on observed correlations from a loophole-free Bell test conducted across a network, addressing vulnerabilities present in hardware-dependent systems. Experiments employed two verifiers separated by a distance of 195.1(3) metres, performing 335 instances of the protocol over a two-day period. Each instance comprised a sequence of trials where measurement outcomes and messages were meticulously recorded to determine successful position verification.
The team constrained the amount of prior entanglement shared between adversaries, establishing a security bound of 8×10−6 average robustness of entanglement across trials. This innovative approach leverages the principles of faster-than-light signalling impossibility and constraints on three-party non-signaling correlations to ensure security. Researchers meticulously analysed inputs and outputs from experimental devices to achieve device-independent security, minimizing assumptions about the internal workings of the quantum devices.

Quantum localization beats classical limits

Scientists have achieved a breakthrough in secure remote localization, demonstrating a device-independent protocol for position verification that guarantees security using only observed correlations from a loophole-free Bell test across a network. The study considered adversaries capable of controlling all untrusted hardware, possessing unlimited computation, and constrained only by causality during a trial, but assumed limited entanglement shared before each test. Measurements confirm that the target region size is determined by the speed of light and four time intervals: ∆τ1 = (rA −sA)/2, ∆τ2 = (rB −sB)/2, ∆τ3 = rA −sB, and ∆τ4 = rB −sA. Tests prove that the intersection of spheres and prolate ellipsoids, defined by these time intervals, determines the achievable localization precision. Specifically, the single-prover target region, Ssingle = S(A, c∆τ1) ∩S(B, c∆τ2) ∩ E(A, B; c∆τ3) ∩E(A, B; c∆τ4), was significantly reduced compared to classical methods.

Quantum position verification surpasses classical limits, offering enhanced

Scientists have demonstrated the first complete quantum position verification protocol, representing a significant advance in secure quantum cryptography. While the current demonstration provides robust security within minutes, the authors acknowledge limitations related to transmission speeds and device latencies, which currently prevent achieving ideal performance. Future research could focus on improving transmission speeds, reducing processing delays, and excluding adversaries with stronger entanglement, potentially leading to even more precise and rapid localization. Exploring protocols where both the entangled photon source and measurement stations are untrusted and remotely located represents a compelling direction for further investigation.