近日，日本东京大学的K. Yoshioka&A. Ishida及其研究团队取得一项新进展。经过不懈努力，他们利用啁啾激光脉冲串将正电子素冷却到超低速度。相关研究成果已于2024年9月11日在国际权威学术期刊《自然》上发表。

本研究展示了正电子素的一维激光冷却。为克服正电子素寿命短暂、多普勒展宽及反冲效应带来的主要挑战，研究人员采用了一种创新的激光系统，该系统能发射一系列中心频率连续增加的宽带脉冲。通过一维啁啾冷却技术，研究人员在100纳秒内将部分稀释的正电子素气体冷却至约1开尔文的速度分布。

作为反物质低温基础物理学领域的一项重大进展，这项针对纯轻子系统的研究补充了关于含强子的奇异原子——反氢的研究。正电子素激光冷却的成功应用，为严格测试束缚态量子电动力学提供了独特机遇，并有望在这一物质-反物质系统中实现玻色-爱因斯坦凝聚。

据悉，当巧妙地应用激光辐射时，原子和分子可以被冷却，从而实现量子系统的精确测量和控制。这对于物理学基础研究以及精密光谱学、具有量子统计特性的超冷气体和量子计算等实际应用至关重要。在激光冷却过程中，原子通过反复吸收激光光子并在随机方向上自发发射，从而减速到原本无法达到的速度。简单的系统可以作为基础物理学的严格试验场——其中一个例子就是纯轻子型的正电子素，这是一种由一个电子及其反粒子（正电子）组成的奇异原子。然而，迄今为止，正电子素的激光冷却尚未实现。

附：英文原文

Title: Cooling positronium to ultralow velocities with a chirped laser pulse train

Author: Shu, K., Tajima, Y., Uozumi, R., Miyamoto, N., Shiraishi, S., Kobayashi, T., Ishida, A., Yamada, K., Gladen, R. W., Namba, T., Asai, S., Wada, K., Mochizuki, I., Hyodo, T., Ito, K., Michishio, K., ORourke, B. E., Oshima, N., Yoshioka, K.

Issue&Volume: 2024-09-11

Abstract: When laser radiation is skilfully applied, atoms and molecules can be cooled, allowing the precise measurements and control of quantum systems. This is essential for the fundamental studies of physics as well as practical applications such as precision spectroscopy, ultracold gases with quantum statistical properties and quantum computing. In laser cooling, atoms are slowed to otherwise unattainable velocities through repeated cycles of laser photon absorption and spontaneous emission in random directions. Simple systems can serve as rigorous testing grounds for fundamental physics—one such case is the purely leptonic positronium, an exotic atom comprising an electron and its antiparticle, the positron. Laser cooling of positronium, however, has hitherto remained unrealized. Here we demonstrate the one-dimensional laser cooling of positronium. An innovative laser system emitting a train of broadband pulses with successively increasing central frequencies was used to overcome major challenges posed by the short positronium lifetime and the effects of Doppler broadening and recoil. One-dimensional chirp cooling was used to cool a portion of the dilute positronium gas to a velocity distribution of approximately 1K in 100ns. A major advancement in the field of low-temperature fundamental physics of antimatter, this study on a purely leptonic system complements work on antihydrogen, a hadron-containing exotic atom. The successful application of laser cooling to positronium affords unique opportunities to rigorously test bound-state quantum electrodynamics and to potentially realize Bose–Einstein condensation in this matter–antimatter system.

DOI: 10.1038/s41586-024-07912-0

Source: https://www.nature.com/articles/s41586-024-07912-0