Gláucia Murta

Secure communication is a core task in cryptography which is focused on protecting the content of a message against eavesdroppers. In certain scenarios, however, the identities of the communicating parties are themselves sensitive and must remain concealed. This calls for anonymous communication protocols that ensure not only message secrecy but also the privacy of participants' identities. In this talk, I will present recent advances showing how quantum systems can offer advantages for anonymous communication in network settings. I will introduce a security framework that encompasses the secrecy of a shared key and the anonymity of the communicating users and show how the correlations of multipartite Greenberger-Horne-Zeilinger (GHZ) states enable protocols that outperform those based on bipartite entanglement. I will also highlight a recent experimental realization that demonstrates that these advantages are already accessible with current technology. Finally, I will outline open questions and possible directions for future research in this emerging area.

Quantum key distribution (QKD) enables the exchange of cryptographic keys with information-theoretic security. However, real-world implementations of QKD are often limited by noise, losses, and imperfect devices. High-dimensional quantum systems offer a promising route to overcome these limitations, enabling denser information encoding and enhanced resilience to noise and loss compared to traditional qubit-based protocols. On the other hand, device-independent (DI) protocols can address all adversarial cases due to device imperfections; however, existing security proofs have not shown any advantage associated with higher dimensions. In this work, we present a robust high-dimensional one-sided DI-QKD (1sDI-QKD) protocol whose security is certified through violations of quantum steering inequalities. By relaxing assumptions on one of the parties while still leveraging high dimensions, this approach improves the practicality of the protocols over fully device-independent QKD, offering promising experimental implications. We investigate 1sDI-QKD utilizing high-dimensional entanglement systems based on Srivastav et al. [PhysRevX.12.041023] framework and show that reverse reconciliation leverages the inherent asymmetry of the steering scenario, resulting in significantly higher key rates in the asymptotic regime as we increase the dimensions. Furthermore, we analyze the protocol's robustness to depolarizing noise and detection inefficiencies. Our results demonstrate the enhanced noise robustness and loss tolerance of high-dimensional 1sDI-QKD. The next step will be to experimentally validate these advantages, establishing high-dimensional 1sDI-QKD as a strong candidate for secure quantum communication under realistic conditions.

Here we report on the experimental results implementing robust anonymous quantum conference key agreement using GHZ states. Results confirm the advantage when allowing for the use of multipartite entanglement along with bipartite entanglement.