Spatio-temporal traces of information

• Applicant: Professorin Dr. Ramona Wolf
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 559916168

In quantum information theory, information is typically seen as abstract and independent of its physical carrier, implicitly assuming a well-defined location in spacetime. However, especially in the quantum realm, this abstraction can break down due to phenomena like non-locality and entanglement. Thus, information cannot always be confined to specific regions, raising concerns about secure storage and transfer. This issue is especially relevant in quantum key distribution (QKD) protocols, where the precise location of information is vital for protecting sensitive data, such as cryptographic keys, from adversaries. As quantum technologies evolve, understanding the spatio-temporal behaviour of quantum information is critical for developing secure communication systems. To address these challenges, it is important to study how reference frames—the perspectives from which quantum systems are described—affect information localisation and security. Classical reference frames provide a basis for aligning devices; however, in a fully quantum context, these references can be quantum systems, adding complexities from superposition and entanglement. By incorporating both classical and quantum reference frames into cryptographic protocols, we explore how information is transferred and exploited by adversaries, establishing a security framework that reflects the behaviour of quantum information in physical space and time. The first objective is to integrate classical reference frames into QKD security frameworks and investigate how adversaries might exploit their alignment procedure in a QKD protocol. The research extends existing security proof techniques, challenging the assumption that QKD protocols are secure without considering physical alignment. Next, we introduce quantum reference frames (QRFs), where quantum systems serve as reference points. Here, the third particle paradox shows how adding a particle to an entangled system can alter the information's location unexpectedly. The project aims to examine how QRFs impact secrecy and extend the QKD security framework to account for the quantum nature of reference systems. Finally, the study extends to quantum gravity, where the concept of subsystems—essential for security—becomes ambiguous, challenging the assumption that information can be securely stored in a laboratory. The project will develop methods to approximate subsystem structures in these contexts, forming a foundation for studying quantum information processing tasks in quantum gravity. Our research advances quantum cryptography by incorporating the quantum description of all protocol components and reintroducing previously abstracted aspects of spacetime. It also deepens our understanding of quantum reference frames, clarifying their impact on information localisation and secure communication in adversarial scenarios. These insights will contribute to the theoretical foundations and practical applications of quantum technologies.

• DFG Programme: Research Grants
• International Connection: Austria, Switzerland
• Partner Organisation: Schweizerischer Nationalfonds (SNF)
• Cooperation Partners: Dr. Linqing Chen; Professor Dr. Renato Renner