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.
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 \ensuremathσX,\ensuremathσZ 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.
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.
Abstract Device-independent certification of quantum devices is of crucial importance for the development of secure quantum information protocols. So far, the most studied scenario corresponds to a system consisting of different non-characterized devices that observers probe with classical inputs to obtain classical outputs. The certification of relevant quantum properties follows from the observation of correlations between these events that do not have a classical counterpart. In the fully device-independent scenario no assumptions are made on the devices and therefore their non-classicality follows from Bell non-locality. There exist other scenarios, known as semi-device-independent, in which assumptions are made on the devices, such as their dimension, and non-classicality is associated to the observation of other types of correlations with no classical analogue. More recently, the use of trusted quantum inputs for certification has been introduced. The goal of this work is to study the power of this formalism and describe self-testing protocols in various settings using trusted quantum inputs. We also relate these different types of self-testing to some of the most basic quantum information protocols, such as quantum teleportation. Finally, we apply our findings to quantum networks and provide methods for estimating the quality of the whole network, as well as of parts of it.
Position information underpins many modern technologies, from navigation and timing to authentication and critical infrastructure. However, classical methods of proving that information originates from a particular position are vulnerable to spoofing. This limitation can be overcome with quantum technologies but current protocols rely on trust in quantum hardware that can be undermined, or require quantum computers and bounds on adversarial computation. Nevertheless, there has been significant interest in experimental demonstrations, and aspects of these protocols have been implemented. Here we introduce and experimentally demonstrate the Bell-test quantum position verification protocol for device-independent quantum position verification that guarantees security with only observed correlations from a loophole-free Bell test across a quantum network. We experimentally implement a version of this device-independent protocol against adversaries who, before each trial, are weakly entangled. Our demonstration achieves a one-dimensional localization 2.47(2) times smaller than the best, necessarily non-remote, classical localization protocol. Compared to classical protocols with identical latencies, the localization volume is 4.53(5) times smaller, and represents a certifiable quantum advantage. The general Bell-test protocol is loss tolerant and secure against adversaries with significant quantum resources. This work allows digital security to be anchored to physically trusted locations, enabling new position-based authentication protocols for applications such as financial transactions, legal agreements, and securing critical infrastructure.
Device-independent certification of quantum devices is of crucial importance for the development of secure quantum information protocols. So far, the most studied scenario corresponds to a system consisting of different non-characterized devices that observers probe with classical inputs to obtain classical outputs. The certification of relevant quantum properties follows from the observation of correlations between these events that do not have a classical counterpart. In the fully device-independent scenario no assumptions are made on the devices and therefore their non-classicality follows from Bell non-locality. There exist other scenarios, known as semi-device-independent, in which assumptions are made on the devices, such as their dimension, and non-classicality is associated to the observation of other types of correlations with no classical analogue. More recently, the use of trusted quantum inputs for certification has been introduced. The goal of this work is to study the power of this formalism and describe self-testing protocols in various settings using trusted quantum inputs. We also relate these different types of self-testing to some of the most basic quantum information protocols, such as quantum teleportation. Finally, we apply our findings to quantum networks and provide methods for estimating the quality of the whole network, as well as of parts of it.
We demonstrate one-sided device-independent self-testing of any pure two-qubit entangled state based on a fine-grained steering inequality. The maximum violation of a fine-grained steering inequality can be used to witness certain steerable correlations, which certify all pure two-qubit entangled states. Our experimental results identify which particular pure two-qubit entangled state has been self-tested and which measurement operators are used on the untrusted side. Furthermore, we analytically derive the robustness bound of our protocol, enabling our subsequent experimental verification of robustness through state tomography. Finally, we ensure that the requisite no-signaling constraints are maintained in the experiment.
Quantum entanglement is the key resource for quantum information processing. Device-independent certification of entangled states is a long standing open question, which arouses the concept of self-testing. The central aim of self-testing is to certify the state and measurements of quantum systems without any knowledge of their inner workings, even when the used devices cannot be trusted. Specifically, utilizing Bell's theorem, it is possible to place a boundary on the singlet fidelity of entangled qubits. Here, beyond this rough estimation, we experimentally demonstrate a complete self-testing process for various pure bipartite entangled states up to four dimensions, by simply inspecting the correlations of the measurement outcomes. We show that this self-testing process can certify the exact form of entangled states with fidelities higher than 99.9% for all the investigated scenarios, which indicates the superior completeness and robustness of this method. Our work promotes self-testing as a practical tool for developing quantum techniques.