The fundamental precision limit of atomic interference measurements using uncorrelated particles is represented by Standard Quantum Limit (SQL), which results by averaging the random fluctuations in repeated single particle measurements. It is possible to overcome this limit inducing quantum correlations between the atoms to obtain a spin squeezed state. The reduction of quantum noise for one component of the collective spin vector is expected to improve the precision of atom interferometers as well as of atom clocks.
An apparatus based on a folded high finesse optical cavity placed in vacuum is developed to obtain high degree of squeezing for 87Rb atoms. A laser at 1560 nm injected on the fundamental mode of the cavity will optically trap the atoms. A laser beam at 780 nm resonant with the cavity will provide the tool for the quantum non-demolition measurement inducing spin squeezing. Using multi-frequencies schemes and heterodyne detection techniques it is possible to cancel out several uncertainty sources, as well as measuring both the absolute and the differential population on the two hyperfine levels of the ground state.
The experiment presents several innovative solutions, like the production of an all-optical BEC in a cavity and the adoption of the folded geometry for the latter. We plan to study novel cooling techniques for neutral atoms coupled to the modes of the optical cavity. Finally, the setup will be used to realise continuos measurement atom interferometry, for example with the "bounching" scheme, with the possibility to implement quantum feedback schemes.