Speaker
Description
Positronium and muonium, as purely leptonic atoms without internal structure, provide ideal systems for precision tests of quantum electrodynamics (QED) and searches for new physics [1].
We report a new measurement of the positronium $1^3S_1 \to 2^3S_1$ transition frequency using two-photon continuous-wave laser spectroscopy, $\nu = 1233607224.1(6.0)\ \mathrm{MHz}$ [2].
Our result agrees with the previous 2.6 ppb determination [3] and with state-of-the-art QED calculations at order $\mathcal{O}(\alpha^7 \ln^2(1/\alpha))$, which predict $1233607222.12(58)\ \mathrm{MHz}$ [1].
Combining the two experimental results gives $1233607218.1(2.8)\ \mathrm{MHz}$, reducing the tension with QED to about $1.4\sigma$.
We also present a semi-analytical lineshape model including finite lifetime effects, photoionization, and AC Stark shifts. The model agrees with detailed simulations and experimental data and is directly applicable to other unstable systems such as muonium.
In parallel, we report progress toward an improved continuous-wave measurement of the muonium $1S \to 2S$ transition[4]. A high-power UV laser system delivering intracavity powers above $40~$W has demonstrated stable multi-day operation, and background rates are below one event per day. Commissioning measurements with hydrogen validate the excitation and detection scheme. The setup is ready for a first CW measurement of this transition.
We will also discuss future prospects using a Ramsey-Doppler excitation scheme for next-generation positronium and muonium experiments [5].
[1] G. S. Adkins et al., Phys. Rep. 975, 1 (2022).
[2] L. de Sousa Borges et al., Phys. Rev. A (2026, in press).
[3] M. S. Fee et al., Phys. Rev. Lett. 70, 1397 (1993).
[4] N. Zhadnov et al., Optics Express 31 (2023).
[5] E. Javary et al., Eur. Phys. J. D 79, 15 (2025).