Speaker
Description
As purely leptonic atoms lacking internal structure, positronium constitutes an ideal system for high-precision tests of bound state quantum electrodynamics (QED) and search for new physics [1]. We report our results on the $\text{1}^\text{3}\text{S}_\text{1} \to \text{2}^\text{3}\text{S}_\text{1}$ interval in positronium, measured via two-photon optical spectroscopy using a continuous-wave laser. Our measurement with an uncertainty of 6 MHz (4.9 ppb) [3] is consistent with the most precise measurement reported to date (2.6 ppb) [2]. Combining these two results reduces the tension with the theory at the $1.4\sigma$ level. With ongoing upgrades of the experimental setup, we expect to improve the measurement in the near future, aiming for a precision of 500 kHz ($\sim$0.4 ppb) to match the theoretical one (0.47 ppb) [1].
Additionally, we will present a semi-analytical model that we have developed to characterise the lineshape of the $\text{1}^\text{3}\text{S}_\text{1} \to \text{2}^\text{3}\text{S}_\text{1}$ interval in positronium. This model builds upon previous theoretical frameworks applied to stable atomic systems [4,5] and demonstrates excellent agreement with Monte Carlo simulations and experimental validations [2]. This approach serves as a valuable tool for optimising experimental parameters and provides deeper theoretical insights without requiring extensive computational resources.
Finally, we present future long-term directions for positronium spectroscopy, particularly the implementation of a novel Ramsey-Doppler spectroscopy scheme [6]. This innovative technique has the potential to outperform current state-of-the-art by at least two orders of magnitude.
References
[1] G. S. Adkins, D. B. Cassidy, and J. Pérez-Ríos, Phys. Rept. 975, 1 (2022).
[2] L. d. S. Borges, E. Thorpe-Woods, E. Javary, and P. Crivelli, Precision continuous-wave laser measurement of the $\text{1}^\text{3}\text{S}_\text{1} \to \text{2}^\text{3}\text{S}_\text{1}$ interval in positronium (2025).
[3] M. S. Fee, A. P. Mills, S. Chu, E. D. Shaw, K. Danzmann, R. J. Chichester, and D. M. Zuckerman, Phys.Rev. Lett. 70, 1397 (1993).
[4] L. O. A. Azevedo and C. L. Cesar, Phys. Rev. A 111, 012807 (2025).
[5] R. A. Gustafson and F. Robicheaux, Journal of Physics B: Atomic, Molecular and Optical Physics 54,185001 (2021).
[6] E. Javary, E. Thorpe-Woods, I. Cortinovis, M. Mähring, L. de Sousa Borges, and P. Crivelli, The European Physical Journal D 79, 10.1140/epjd/s10053-025-00960-9 (2025).