Motivations and Needs Atomic clocks have been and will be a key technology in a broad range of applications spanning from tests of fundamental physical theories (e. g. general relativity, stability of fundamental constants), to daily use technologies (e. g. telecommunications, satellite navigation and radars). Optical clocks, in virtue of their higher accuracy, emerged as a strong candidate for the redefinition of the second as clearly stated in EURAMET roadmaps, and will open new scientific and technological applications, already emerging on the horizon (relativistic geodesy, improved Very Long Baseline Interferometry). Most advanced quantum technologies can surpass the classical noise levels present in optical clocks, allowing better and more stable clocks. To fully exploit the potential offered by QT, it is necessary to realize new quantum engineered states allowing in general to create cooperative behaviours of atomic or ionic ensembles. These advancements also support the development of quantum information processing and quantum simulation. These techniques have been proved in various quantum systems (mostly in the RF and microwave domains), but have not been employed at a metrologically relevant level yet. The project will study novel techniques for optical oscillators and quantum sensors, to achieve uncertainties of 10-18 in measurement time scales from minutes to hours. Scientific Excellence Atomic clocks today are still “first generation” quantum devices, where extremely accurate spectroscopic measurements are performed using uncoherent ensembles of independent quantum particles. The possibility to realize a “second generation” of clocks, further exploiting the possibilities opened by quantum mechanics, represent a high level scientific goal, that combines scientific excellence and fundamental metrology. Our goal is to realize second generation quantum enhanced optical clocks, surpassing the most advanced optical clocks, using smart quantum techniques, to open the 10-19 accuracy range. Highly innovative elements of this clock approach will be: • Spin squeezing and entanglement of atom or ions to approach the Heisenberg noise limit • Narrow line width super radiant laser emission to overcome the cavity thermal noise limit. The project goal will be achieved through a joint effort between frequency metrologists and quantum technology experts, capable of combining new quantum mechanical tools in quantum state engineering with clock and frequency metrology concepts. Work packages WP1 – Methods towards spin squeezed systems WP2 – Creating entanglement in strongly coupled systems WP3 – Active frequency standards WP4 – Evaluation of accuracy and of improved stability WP5 – Impact
