Measurement of the $\text{1}^\text{3}\text{S}_\text{1} \to \text{2}^\text{3}\text{S}_\text{1}$ interval in positronium using field-ionization of Rydberg states

TL;DR

This paper presents a highly precise measurement of the positronium 1^3S_1 to 2^3S_1 transition using advanced laser spectroscopy and field-ionization, reducing systematic uncertainties and enabling future high-precision tests of quantum electrodynamics.

Contribution

The study introduces a novel pulsed two-photon spectroscopy method combined with Monte-Carlo simulations and heterodyne laser measurements to improve precision in positronium transition measurements.

Findings

Measured the transition at 1,233,607,210.5 ± 49.6 MHz.

Achieved 40 ppb measurement precision.

Demonstrated a technique to correct for Doppler and AC Stark effects.

Abstract

We report a new 40 ppb measurement of the positronium $\text{1}^\text{3}\text{S}_\text{1} \to \text{2}^\text{3}\text{S}_\text{1}$ interval using pulsed two-photon optical spectroscopy. The transition is detected via field-ionization of atoms excited from the 2S to the 20P Rydberg state. Precise Monte-Carlo line-shape simulations allow for the accounting of effects such as Doppler and AC Stark shifts, while an optical heterodyne measurement of the excitation laser pulse is used to correct for laser frequency chirp. A value of $1\,233\,607\,210.5\pm 49.6\, \mathrm{MHz}$ was obtained. This scheme allows for the measurement of the velocity distribution of positronium atoms to correct for the second-order Doppler effect. This is the major source of systematic uncertainty expected for future measurements of this transition with a CW laser, thus, our technique paves the way toward a new generation of a high precision determination of this interval in positronium.