Polarons are among the most fundamental quasiparticles emerging in interacting many-body systems, forming already at the level of a single mobile dopant [1]. In the context of the twodimensional Fermi-Hubbard model, such polarons are predicted to form around charged dopants in an antiferromagnetic background in the low doping regime close to the Mott insulating state [2][3][4][5][6][7][8]. Macroscopic transport and spectroscopy measurements related to high Tc materials have yielded strong evidence for the existence of such quasiparticles in these systems [9,10]. Here we report the first microscopic observation of magnetic polarons in a doped Fermi-Hubbard system, harnessing the full single-site spin and density resolution of our ultracold-atom quantum simulator. We reveal the dressing of mobile doublons by a local reduction and even sign reversal of magnetic correlations, originating from the competition between kinetic and magnetic energy in the system. The experimentally observed polaron signatures are found to be consistent with an effective string model at finite temperature [8]. We demonstrate that delocalization of the doublon is a necessary condition for polaron formation by contrasting this mobile setting to a scenario where the doublon is pinned to a lattice site. Our work paves the way towards probing interactions between polarons, which may lead to stripe formation, as well as microscopically exploring the fate of polarons in the pseudogap and bad metal phase. arXiv:1811.06907v1 [cond-mat.quant-gas]

Elementary particles carry several quantum numbers, such as charge and spin. However, in an ensemble of strongly interacting particles, the emerging degrees of freedom can fundamentally differ from those of the individual constituents. For example, one-dimensional systems are described by independent quasiparticles carrying either spin (spinon) or charge (holon). Here, we report on the dynamical deconfinement of spin and charge excitations in real space after the removal of a particle in Fermi-Hubbard chains of ultracold atoms. Using space- and time-resolved quantum gas microscopy, we tracked the evolution of the excitations through their signatures in spin and charge correlations. By evaluating multipoint correlators, we quantified the spatial separation of the excitations in the context of fractionalization into single spinons and holons at finite temperatures.

We investigate the use of light assisted collisions for the deterministic preparation of individual atoms in a microtrap. Blue detuned light is used in order to ensure that only one of the collision partners is lost from the trap. We obtain a 91% loading efficiency of single 85 Rb atoms. This can be achieved within a total preparation time of 542 ms. A numerical model of the process quantitatively agrees with the experiment giving an in-depth understanding of the dynamics of the process and allowing us to identify the factors that still limit the loading efficiency. The fast loading time in combination with the high efficiency may be sufficient for loading quantum registers at the size required for competitive quantum computing.