The photon—the quantum excitation of the electromagnetic field—is massless but carries momentum. A photon can therefore exert a force on an object upon collision¹. Slowing the translational motion of atoms and ions by application of such a force^2,3, known as laser cooling, was first demonstrated 40 years ago^4,5. It revolutionized atomic physics over the following decades^6,7,8, and it is now a workhorse in many fields, including studies on quantum degenerate gases, quantum information, atomic clocks and tests of fundamental physics. However, this technique has not yet been applied to antimatter. Here we demonstrate laser cooling of antihydrogen⁹, the antimatter atom consisting of an antiproton and a positron. By exciting the 1S–2P transition in antihydrogen with pulsed, narrow-linewidth, Lyman-α laser radiation^10,11, we Doppler-cool a sample of magnetically trapped antihydrogen. Although we apply laser cooling in only one dimension, the trap couples the longitudinal and transverse motions of the anti-atoms, leading to cooling in all three dimensions. We observe a reduction in the median transverse energy by more than an order of magnitude—with a substantial fraction of the anti-atoms attaining submicroelectronvolt transverse kinetic energies. We also report the observation of the laser-driven 1S–2S transition in samples of laser-cooled antihydrogen atoms. The observed spectral line is approximately four times narrower than that obtained without laser cooling. The demonstration of laser cooling and its immediate application has far-reaching implications for antimatter studies. A more localized, denser and colder sample of antihydrogen will drastically improve spectroscopic^11,12,13 and gravitational¹⁴ studies of antihydrogen in ongoing experiments. Furthermore, the demonstrated ability to manipulate the motion of antimatter atoms by laser light will potentially provide ground-breaking opportunities for future experiments, such as anti-atomic fountains, anti-atom interferometry and the creation of antimatter molecules.

光子——电磁场的量子激发——是无质量的，但带有动量。^{因此，光子可以在碰撞1}时对物体施加力。通过施加这种力^2,3减慢原子和离子的平移运动，称为激光冷却，40 年前首次证明^4,5。在接下来的几十年中，它彻底改变了原子物理学^6,7,8，现在它已成为许多领域的主力军，包括量子简并气体研究、量子信息、原子钟和基础物理学测试。然而，这项技术尚未应用于反物质。在这里，我们演示了反氢^{9的激光冷却}，由反质子和正电子组成的反物质原子。通过用脉冲、窄线宽、Lyman-α 激光辐射激发反氢中的 1S–2P 跃迁^10,11，我们对磁性捕获的反氢样本进行多普勒冷却。虽然我们只在一个维度上应用激光冷却，但陷阱耦合了反原子的纵向和横向运动，导致所有三个维度的冷却。我们观察到中值横向能量减少了一个数量级以上 - 相当一部分反原子获得亚微电子伏横向动能。我们还报告了对激光冷却的反氢原子样品中激光驱动的 1S-2S 跃迁的观察。观察到的谱线大约比没有激光冷却的谱线窄四倍。激光冷却的演示及其直接应用对反物质研究具有深远的影响。更加本土化，^11,12,13和引力¹⁴在正在进行的实验中对反氢的研究。此外，所展示的通过激光操纵反物质原子运动的能力将为未来的实验提供开创性的机会，例如反原子喷泉、反原子干涉测量和反物质分子的产生。