Thomas K F, Ross J A, Henson B M, Shin D K, Baldwin K G H, Hodgman S S, Truscott A G
Laser Physics Centre, Research School of Physics, The Australian National University, Canberra, ACT 2601, Australia.
Phys Rev Lett. 2020 Jul 3;125(1):013002. doi: 10.1103/PhysRevLett.125.013002.
We present the detection of the highly forbidden 2^{3}S_{1}→3^{3}S_{1} atomic transition in helium, the weakest transition observed in any neutral atom. Our measurements of the transition frequency, upper state lifetime, and transition strength agree well with published theoretical values and can lead to tests of both QED contributions and different QED frameworks. To measure such a weak transition, we develop two methods using ultracold metastable (2^{3}S_{1}) helium atoms: low background direct detection of excited then decayed atoms for sensitive measurement of the transition frequency and lifetime, and a pulsed atom laser heating measurement for determining the transition strength. These methods could possibly be applied to other atoms, providing new tools in the search for ultraweak transitions and precision metrology.
我们展示了对氦气中高度禁戒的(2^{3}S_{1}→3^{3}S_{1})原子跃迁的探测，这是在任何中性原子中观测到的最弱跃迁。我们对跃迁频率、上能级寿命和跃迁强度的测量结果与已发表的理论值吻合良好，并且能够对量子电动力学（QED）贡献和不同的QED框架进行检验。为了测量如此微弱的跃迁，我们开发了两种使用超冷亚稳态((2^{3}S_{1}))氦原子的方法：对激发后衰变的原子进行低本底直接探测，以灵敏测量跃迁频率和寿命；以及进行脉冲原子激光加热测量来确定跃迁强度。这些方法有可能应用于其他原子，为寻找超微弱跃迁和精密计量学提供新工具。
