Controlling the interactions between atoms with external fields opened up new branches in physics ranging from strongly correlated atomic systems to ideal Bose¹ and Fermi² gases and Efimov physics^3,4. Such control usually prepares samples that are stationary or evolve adiabatically in time. In contrast, in molecular physics, external ultrashort laser fields are used to create anisotropic potentials that launch ultrafast rotational wave packets and align molecules in free space⁵. Here we combine these two regimes of ultrafast times and low energies. We apply a short laser pulse to the helium dimer, a weakly bound and highly delocalized single bound state quantum system. The laser field locally tunes the interaction between two helium atoms, imparting an angular momentum of 2ℏ and evoking an initially confined dissociative wave packet. We record a video of the density and phase of this wave packet as it propagates from small to large internuclear distances. At large internuclear distances, where the interaction between atoms is negligible, the wave packet is essentially free. This work paves the way for future tomography of wave-packet dynamics and provides the technique for studying exotic and otherwise hardly accessible quantum systems, such as halo and Efimov states.

控制原子与外部场之间的相互作用开辟了物理学的新分支，从高度相关的原子系统到理想的Bose ¹和Fermi ²气体以及Efimov物理学^3,4。这样的对照通常制备固定的样品或在时间上绝热地发展。相反，在分子物理学中，外部超短激光场用于产生各向异性电势，这些电势会发射超快旋转波包并在自由空间中对齐分子⁵。在这里，我们结合了超快时间和低能耗这两种状态。我们向氦二聚体（一个弱束缚和高度离域的单束缚态量子系统）施加短激光脉冲。激光场局部调节两个氦原子之间的相互作用，赋予2 angular的角动量，并引起最初受限的解离波包。我们记录了该波包从小到大核间距离传播时的密度和相位的视频。在大的核间距离处，原子之间的相互作用可忽略不计，波包基本上是自由的。这项工作为波包动力学的未来层析成像铺平了道路，并为研究奇异的和否则难以接近的量子系统（例如晕轮和Efimov态）提供了技术。