Quantum Position Verification with Remote Untrusted Devices
Gautam A. Kavuri, Yanbao Zhang, Abigail R. Gookin, Soumyadip Patra, Joshua C. Bienfang, Honghao Fu, Yusuf Alnawakhtha, Dileep V. Reddy, Michael D. Mazurek, Carlos Abellán, Waldimar Amaya, Morgan W. Mitchell, Sae Woo Nam, Carl A. Miller, Richard P. Mirin, Martin J. Stevens, Scott Glancy, Emanuel Knill, Lynden K. Shalm
quant-phSubmitted Jan 23, 2026• Announced Jan 26, 2026• 0 citations
Many applications require or benefit from being able to securely localize remote parties. In classical physics, adversaries can in principle have complete knowledge of such a party's devices, and secure localization is fundamentally impossible. This limitation can be overcome with quantum technologies, but proposals to date require trusting vulnerable hardware. Here we develop and experimentally demonstrate a protocol for device-independent quantum position verification that guarantees security with only observed correlations from a loophole-free Bell test across a quantum network. The protocol certifies the position of a remote party against adversaries who, before each instance of the test, are weakly entangled, but otherwise have unlimited quantum computation and communication capabilities. Our demonstration achieves a one-dimensional localization that is 2.47(2) times smaller than the best, necessarily non-remote, classical localization protocol. Compared to such a classical protocol having identical latencies, the localization is 4.53(5) times smaller. This work anchors digital security in the physical world.
Many applications require or benefit from being able to securely localize remote parties. In classical physics, adversaries can in principle have complete knowledge of such a party's devices, and secure localization is fundamentally impossible. This limitation can be overcome with quantum technologies, but proposals to date require trusting vulnerable hardware. Here we develop and experimentally demonstrate a protocol for device-independent quantum position verification that guarantees security with only observed correlations from a loophole-free Bell test across a quantum network. The protocol certifies the position of a remote party against adversaries who, before each instance of the test, are weakly entangled, but otherwise have unlimited quantum computation and communication capabilities. Our demonstration achieves a one-dimensional localization that is 2.47(2) times smaller than the best, necessarily non-remote, classical localization protocol. Compared to such a classical protocol having identical latencies, the localization is 4.53(5) times smaller. This work anchors digital security in the physical world.
Abstract Position-based cryptography allows a party to prove its geographic location by responding to challenges from verifiers. Classical position verification is impossible against entangled adversaries. Quantum position verification overcomes this but requires trusted measurement devices at the verifi cation locations. We introduce Device-Independent Position Verification using the Mermin-Ardehali Belinskii-Klyshko four-party Bell inequality. Our protocol uses four verifiers at the corners of a square and a single prover. The MABK inequality has classical bound BMABK ≤ 4, while quantum mechan ics achieves BMABK = 4√2 ≈ 5.657 using the four-qubit Greenberger-Horne-Zeilinger state. We prove security against general quantum adversaries using relativistic no-go theorems and the entropy accumulation theorem. Using realistic experimental parameters (four-photon GHZ state fidelity F = 0.85, detector efficiency η = 0.65), we predict a Bell violation BMABK = 4.25, exceeding the classical bound by 0.25. The protocol tolerates up to 15% noise and achieves verification distances up to 30 km with current technology. This work provides the first practical path to location verification on untrusted hardware.
Quantum communication has demonstrated its usefulness for quantum cryptography far beyond quantum key distribution. One domain is two-party cryptography, whose goal is to allow two parties who may not trust each other to solve joint tasks. Another interesting application is position-based cryptography whose goal is to use the geographical location of an entity as its only identifying credential. Unfortunately, security of these protocols is not possible against an all powerful adversary. However, if we impose some realistic physical constraints on the adversary, there exist protocols for which security can be proven, but these so far relied on the knowledge of the quantum operations performed during the protocols. In this work we improve the device-independent security proofs of Kaniewski and Wehner [New J. Phys. 18, 055004 (2016)] for two-party cryptography (with memoryless devices) and we add a security proof for device-independent position verification (also memoryless devices) under different physical constraints on the adversary. We assess the quality of the devices by observing a Bell violation, and, as for Kaniewski and Wehner [New J. Phys. 18, 055004 (2016)], security can be attained for any violation of the Clauser-Holt-Shimony-Horne inequality.
Bell non-locality between distant quantum systems—that is, joint correlations which violate a Bell inequality—can be verified without trusting the measurement devices used, nor those performing the measurements. This leads to unconditionally secure protocols for quantum information tasks such as cryptographic key distribution. However, complete verification of Bell non-locality requires high detection efficiencies, and is not robust to typical transmission losses over long distances. In contrast, quantum or Einstein–Podolsky–Rosen steering, a weaker form of quantum correlation, can be verified for arbitrarily low detection efficiencies and high losses. The cost is that current steering-verification protocols require complete trust in one of the measurement devices and its operator, allowing only one-sided secure key distribution. Here we present measurement-device-independent steering protocols that remove this need for trust, even when Bell non-locality is not present. We experimentally demonstrate this principle for singlet states and states that do not violate a Bell inequality. Quantum steering is a form of quantum non-locality that can be verified for arbitrarily low detection efficiencies and high losses at the price of requiring complete trust in one of the parties. Here, Kocsis et al. present measurement-device-independent steering protocols that remove this need for trust.
The phenomenal progress in quantum technologies over the past decades has laid the groundwork for the construction of quantum networks, which will channel the power of quantum theory to guarantee secure and efficient communication, computation, and much more. This thesis studies the notion of trust in quantum networks. In our information age, protecting the security or anonymity of data is a key requirement. We investigate certain protocols that are fundamental to the operation and applications of quantum networks, and propose ways to test and analyse their security, in spite of adversarial intervention. Our focus is on practical methods of verifying the untrusted components, which could be incorporated into realistic networks in the near future. To begin, we propose a protocol for authenticated communication of quantum messages, by verifying the entanglement required for quantum teleportation in an experimentally feasible way. We model the performance of our scheme in the presence of noise. Furthermore, we explore such an authenticated teleportation in the one-sided device-independent scenario, where some devices used for verification may be corrupted. We derive error-tolerant self- testing bounds and extend our results to a realistic experimental setting, demonstrating the compatibility of our protocol with state-of-the-art technology. We then study anonymity, an essential feature for communication across networks. Combining the power of classical and quantum subroutines, we build a practical protocol for anonymous communication of quantum messages, without the need to trust the players in our network, their computational power, or the entanglement they share. We end by considering the verification of graph states distributed across a network of possibly dishonest players, applying our scheme to specific graph states that are central to quantum communication and computation schemes.
Device-independent quantum cryptography allows security even if the devices used to execute the protocol are untrusted - whether this is due to unknown imperfections in the implementation, or because the adversary himself constructed them to subvert the security of the protocol. While device-independence has seen much attention in the domain of quantum key distribution, relatively little is known for general protocols. Here we introduce a new model for device-independence for two-party protocols and position verification in the noisy-storage model. For the first time, we show that such protocols are secure in the most general device-independent model in which the devices may have arbitrary memory, states and measurements. In our analysis, we make use of a slight modification of a beautiful new tool developed in [arXiv:1607.01796] called "Entropy Accumulation Theorem". What's more, the protocols we analyze use only simple preparations and measurements, and can be realized using any experimental setup able to perform a CHSH Bell test. Specifically, security can be attained for any violation of the CHSH inequality, where a higher violation merely leads to a reduction in the amount of rounds required to execute the protocol.
We introduce a protocol for authenticated teleportation, which can be proven secure even when the receiver does not trust his or her measurement devices, and which is experimentally accessible. We use the technique of self-testing from the device-independent approach to quantum information, where we can characterize quantum states and measurements from the exhibited classical correlations alone. First, we derive self-testing bounds for the Bell state and Pauli ${\ensuremath{\sigma}}_{X},{\ensuremath{\sigma}}_{Z}$ measurements, that are robust enough to be implemented in the laboratory. Then, we use these to determine a lower bound on the fidelity of an untested entangled state to be used for teleportation. Finally, we apply our results to propose a protocol for one-sided device-independent authenticated teleportation that is experimentally feasible in both the number of copies and fidelities required. This can be interpreted as a practical authentication of a quantum channel, with additional one-sided device independence.