Quantum Limits to Time Transfer – Qualitime

Exchanging light pulses to perform accurate space-time positioning is a paradigmatic issue of physics. From a fundamental point of view it is the technique used to synchronize clocks situated at remote locations that is at the root of Einstein's concept of space and time. From a more practical point of view, it permits to distribute the time standard over the whole earth and to precisely know the relative position of different satellites in space, applications which require more and more precise positioning and where the limit imposed by the quantum nature of light is at reach. Hence, it is a requirement for the further evolution of this field that the actual quantum limits be demonstrated, both theoretically and experimentally, and that ways of going beyond them be proposed. The central objective of this project is to identify the limit in time transfer imposed by the fundamental quantum fluctuations of the optical link, both theoretically and experimentally. This work will be based on the merging of concepts from information theory, coherent laser pulses, multimode quantum optics and time resolved interferometry. In order to reach that objective, the project is organised around one main experiment and puts together three groups: one specialised in quantum optics and information extraction at and beyond the quantum limit, one specialised in femtosecond coherent spectroscopy using interferometry and pulse shaping and one theoretical group specialised on quantum limits in measurement instruments. The complementary competences of these three groups, each of them very active in its respective area, are a unique opportunity to reach the objective, and would give to French research an important lead in this fundamental and yet unexplored issue. More specifically, we plan to : - realise a model experiment to reach the standard quantum limit in time transfer; - study the optimal configuration to extract the information from the light beam and implement it experimentally; - study the possibility to go beyond the standard quantum limit, both theoretically and experimentally; - assess the relevance to future fundamental physics experiments.