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We report the efficient and fast (∼2 Hz) preparation of randomly loaded one-dimensional (1D) chains of individual 87 Rb atoms and of dense atomic clouds trapped in optical tweezers using an upgraded experimental platform. This platform is designed for the study of atomic ensembles featuring either ordered or disordered distributions of the atomic positions. It is composed of two high-resolution optical systems perpendicular to each other, enhancing observation and manipulation capabilities. The setup includes a dynamically controllable telescope, which we use to vary the tweezer beam waist. A -enhanced gray molasses on the D1 line enhances the loading of the traps from a magneto-optical trap. Using these tools, we prepare chains of up to ∼100 atoms separated by ∼1 μm by retroreflecting the tweezer light, hence producing a 1D optical lattice with strong transverse confinement. Dense atomic clouds with peak densities up to n 0 ∼ 10 15 atoms/cm 3 are obtained by compression of an initial cloud. This high density results in interatomic distances smaller than λ/(2π ) for the D2 optical transitions, making it ideal to study light-induced interactions in dense samples.

We report a time-resolved study of collective emission in dense ensembles of two-level atoms. We compare, on the same sample, the buildup of superradiance and subradiance from the ensemble when driven by a strong laser. This allows us to measure the dynamics of the population of superradiant and subradiant states as a function of time. In particular, we demonstrate the buildup in time of subradiant states through superradiant dynamics. This illustrates the dynamics of the many-body density matrix of superradiant ensembles of two-level atoms when departing from the ideal conditions of Dicke superradiance, in which symmetry forbids the population of subradiant states.

We observe a non-equilibrium phase transition in a driven dissipative quantum system consisting of an pencilshape cloud of up to N ≈ 2000 laser-cooled atoms in free space, optically excited along its main axis. We find that our data are well reproduced by the Driven Dicke model, which assumes a sub-wavelength sample volume, by simply using an effective atom number. By measuring the excited state population of the atoms and the light emitted in the superradiant mode, we characterize the dynamics of the system and its steady-state properties. In particular, we observe the characteristic N 2 scaling of the photon emission rate in the superradiant phase, thus demonstrating steady-state superradiance in free space. Finally, we observe a modification of the statistics of the superradiant light as we cross the phase transition.

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