We present a thorough experimental investigation of the loading process of laser-cooled atoms from a magneto-optical trap into an optical dipole trap located inside a hollow-core photonic bandgap fiber, followed by propagation of the atoms therein. This, e.g., serves to identify limits to the loading efficiency and thus optical depth which is a key parameter for applications in quantum information technology. Although only limited access in 1D is available to probe atoms inside such a fiber, we demonstrate that a detailed spatially resolved characterization of the loading and trapping process along the fiber axis is possible by appropriate modification of probing techniques combined with theoretical analysis. Specifically, we demonstrate the loading of up to $2.1\times {10}^5$ atoms with a transfer efficiency of $2.1\%$ during the course of 50 ms and a peak loading rate of $4.7\times {10}^3$ atoms ${\mathrm{ms}}^{-1}$ resulting in a peak atomic number density on the order of ${10}^{12}{\mathrm{cm}}^{-3}$. Furthermore, we determine the evolution of the spatial density (profile) and ensemble temperature as it approaches its steady-state value of $T=1400\mu \mathrm{K}$, as well as loss rates, axial velocity and acceleration. The spatial resolution along the fiber axis reaches a few millimeters, which is much smaller than the typical fiber length in experiments. We compare our results to other fiber-based as well as free-space optical dipole traps and discuss the potential for further improvements.

中文翻译：

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空心纤维内冷原子系综的负载和空间分辨表征

我们对激光冷却原子从磁光陷阱加载到位于空芯光子带隙光纤内的光学偶极陷阱中的加载过程进行了彻底的实验研究，然后是原子在其中的传播。例如，这用于确定加载效率的限制，从而确定光学深度，这是量子信息技术应用的关键参数。尽管只能在 1D 中进行有限的访问来探测此类纤维内的原子，但我们证明，通过结合理论分析对探测技术进行适当修改，可以对沿纤维轴的加载和捕获过程进行详细的空间解析表征。具体来说，我们演示了最多加载$2.1\times {10}^5$ 具有转移效率的原子 $2.1\%$ 在 50 ms 的过程中，峰值加载速率为 $4.7\times {10}^3$ 原子 ${\mathrm{小姐}}^{-1}$ 导致峰值原子序数密度为 ${10}^{12}{\mathrm{厘米}}^{-3}$. 此外，我们确定了空间密度（剖面）和集合温度在接近其稳态值时的演变$吨=1400\mu \mathrm{钾}$，以及损失率、轴向速度和加速度。沿光纤轴的空间分辨率达到几毫米，远小于实验中典型的光纤长度。我们将我们的结果与其他基于光纤和自由空间的光学偶极子陷阱进行了比较，并讨论了进一步改进的潜力。