Cooperative emission, superflash and coherent pulse
We investigate the transient coherent transmission of light through an optically thick cold Strontium gas. We observe a coherent superflash just after an abrupt probe extinction, with peak intensity more than 3 times the incident one (see Fig. (a) below). We show that this coherent superflash is a direct signature of the cooperative forward emission of the atoms. By engineering fast transient phenomena on the incident field, we give a clear and simple picture of the physical mechanisms at play. Finally, taking advantage of the fast decay time of the cooperative emission, we create a pulse train of light with a repetition time shorter than the atomic lifetime (see Fig. (b) below). In this regime single atom spontaneous emission can be quenched.

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Geometrical Qubit and non-Abelian gauge field
The symmetry of the Hilbert space is the key feature from which drives remarkable physical properties of a quantum system. U(1) symmetry leads to abelian transformation, whereas a larger symmetry, such as SU(2), leads to non-Abelian gauge field sensitive to paths ordering. We study an adiabatic non-Abelian transformation using a four-level resonant tripod scheme on a laser cooled fermionic strontium gas. As a main result, we show the non-Abelian character of the transformation proceeding the same close loop circulation swapping the path ordering.

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Tuning Casimir-Polder atom/surface interaction with a metamaterial

— Under construction–