Transforming an initial quantum state into a target state through the fastest possible route—a quantum brachistochrone—is a fundamental challenge for many technologies based on quantum mechanics. In two-level systems, the quantum brachistochrone solutions are long known. These solutions, however, are not applicable to larger systems, especially when the target state cannot be reached through a local transformation. Here, we demonstrate fast coherent transport of an atomic wave packet over a distance of 15 times its size—a paradigmatic case of quantum processes going beyond the two-level system. Our measurements of the transport fidelity reveal the existence of a minimum duration—a quantum speed limit—for the coherent splitting and recombination of matter waves. We obtain physical insight into this limit by relying on a geometric interpretation of quantum state dynamics. These results shed light on a fundamental limit of quantum state dynamics and are expected to find relevant applications in quantum sensing and quantum computing.

中文翻译：

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原子远距离状态之间的量子Brachistochrones的演示

通过许多可能的最快途径将初始量子态转变为目标态（量子腕同步）是许多基于量子力学的技术所面临的根本挑战。在两级系统中，量子臂计时解决方案是众所周知的。但是，这些解决方案不适用于大型系统，尤其是当无法通过局部转换来达到目标​​状态时。在这里，我们演示了原子波包在其大小的15倍的距离上的快速相干传输，这是超越两级系统的量子过程的典型案例。我们对传输保真度的测量揭示出存在最小持续时间（量子速度极限），用于物质波的相干分裂和复合。我们通过对量子态动力学的几何解释来获得对该极限的物理见解。这些结果阐明了量子态动力学的基本极限，并有望在量子传感和量子计算中找到相关的应用。