Department of Physics and Astronomy, York University, Toronto, Ontario, M3J 1P3, Canada.
Nature. 2012 Mar 7;483(7390):439-43. doi: 10.1038/nature10942.
The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom's stature lies in its simplicity and in the accuracy with which its spectrum can be measured and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and--by comparison with measurements on its antimatter counterpart, antihydrogen--the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves.
氢原子是现代物理学中最重要和最有影响力的模型系统之一。对其光谱的研究尝试与量子力学的早期历史和发展密不可分。氢原子的重要性在于其简单性，以及其光谱可以被精确测量并与理论相比较。如今，它的光谱仍然是确定基本常数值和挑战现代物理学极限的宝贵工具，包括量子电动力学的有效性——通过与反物质氢原子的对应物——反氢的测量结果进行比较——以及 CPT（电荷共轭、宇称和时间反转）对称性的有效性。在这里，我们报告了一种纯反物质原子的光谱学，证明了反氢的共振量子跃迁。我们已经操纵了反氢原子的内部自旋态，从而诱导出正电子基态的超精细能级之间的磁共振跃迁。我们使用共振微波辐射来翻转磁阱中被捕获的反氢原子中的正电子的自旋。自旋翻转会导致被捕获的反原子从陷阱中被逐出。我们通过比较用微波在共振上辐照时被捕获的原子的存活率与处于微波非共振下的原子的存活率，来寻找共振相互作用的证据。在实验的一种变体中，我们在 110 次微波非共振辐照的捕获尝试中检测到 23 个幸存原子（每次尝试 0.21 个），而在 103 次微波共振辐照的捕获尝试中只有两个原子幸存（每次尝试 0.02 个）。我们还描述了通过微波逐出的反氢原子的湮灭的直接检测。
