Antihydrogen atoms with K or sub-K temperature are a powerful tool to precisely probe the validity of fundamental physics laws and the design of highly sensitive experiments needs antihydrogen with controllable and well defined conditions. We present here experimental results on the production of antihydrogen in a pulsed mode in which the time when 90% of the atoms are produced is known with an uncertainty of ~250 ns. The pulsed source is generated by the charge-exchange reaction between Rydberg positronium atoms—produced via the injection of a pulsed positron beam into a nanochanneled Si target, and excited by laser pulses—and antiprotons, trapped, cooled and manipulated in electromagnetic traps. The pulsed production enables the control of the antihydrogen temperature, the tunability of the Rydberg states, their de-excitation by pulsed lasers and the manipulation through electric field gradients. The production of pulsed antihydrogen is a major landmark in the AE $$\bar{g}$$ḡ IS experiment to perform direct measurements of the validity of the Weak Equivalence Principle for antimatter.

We report on laser cooling of a large fraction of positronium (Ps) in free flight by strongly saturating the $1^{3}S\text{−}{2}^{3}P$ transition with a broadband, long-pulsed 243 nm alexandrite laser. The ground state Ps cloud is produced in a magnetic and electric field-free environment. We observe two different laser-induced effects. The first effect is an increase in the number of atoms in the ground state after the time Ps has spent in the long-lived $2^{3}P$ states. The second effect is one-dimensional Doppler cooling of Ps, reducing the cloud’s temperature from 380(20) to 170(20) K. We demonstrate a 58(9)% increase in the fraction of Ps atoms with $v_{1\text{D}}<3.7\times {10}^4\mathrm{m}{\mathrm{s}}^{-1}$.

We characterized the pulsed Rydberg-positronium production inside the Antimatter Experiment: Gravity, Interferometry, Spectroscopy ($\mathrm{AE}\overline{\text{g}}\mathrm{IS}$) apparatus in view of antihydrogen formation by means of a charge exchange reaction between cold antiprotons and slow Rydberg-positronium atoms. Velocity measurements on the positronium along two axes in a cryogenic environment ($\approx 10\mathrm{K}$) and in $1\mathrm{T}$ magnetic field were performed. The velocimetry was done by microchannel-plate (MCP) imaging of a photoionized positronium previously excited to the $n=3$ state. One direction of velocity was measured via Doppler scan of this $n=3$ line, another direction perpendicular to the former by delaying the exciting laser pulses in a time-of-flight measurement. Self-ionization in the magnetic field due to the motional Stark effect was also quantified by using the same MCP-imaging technique for Rydberg positronium with an effective principal quantum number $n_{\mathrm{eff}}$ ranging between 14 and 22. We conclude with a discussion about the optimization of our experimental parameters for creating Rydberg positronium in preparation for an efficient pulsed production of antihydrogen.

Nanochanneled silicon targets with high positron/positronium (Ps) conversion rate and efficient Ps cooling were produced. Morphological parameters of the nanochannels, such as their diameter and length, were adjusted to get a large fraction of thermalized Ps at room temperature being emitted into vacuum. Ps cooling measurements were conducted combining single-shot positron annihilation lifetime spectroscopy and Doppler spectroscopy of the 1³S → 2³P transition. 2γ–3γ annihilation ratio measurements were also performed to estimate the positron/Ps conversion efficiency. In a converter with nanochannel diameter of 7–10 nm and depth of 3.89 μm, ∼28% of implanted positrons with an energy of 3.3 keV was found to be emitted as Ps with a transverse kinetic energy of 11 ± 2 meV. The reduction of the nanochannels depth to 1.13 μm, without changing the nanochannel diameter, was found to result in a less efficient cooling, highlighting the presence of Ps reflection from the bottom end of nanochannels.

Positronium beam formation and manipulation are required in several fundamental experiments. Efficient positron/positronium conversion in transmission configuration would offer important geometrical advantages over the reflection one for these applications. A novel type of transmission positron/positronium converters, which consists of silicon membranes with pass-through nanochannels, was produced and tested. The amount of forward emitted positronium was studied as a function of the thickness of the membranes and the nanochannel size. A maximum of, at least, $(16\pm 4)\%$ of positrons implanted in $(3.5\pm 0.5)-\mu \mathrm{m}$-thick membrane with a nanochannel size of 5–8 nm were found to be forward emitted as positronium. A similar maximum amount of, at least, $(16\pm 5)\%$, was found to be emitted from a membrane $(7.7\pm 1.3)-\mu \mathrm{m}$-thick with a nanochannel size of 7–10 nm. A preliminary evaluation shows that the maximum amount of forward emitted positronium with the entire kinetic energy distribution below 1 eV is, at least, 9% of the positrons implanted in the $(3.5\pm 0.5)-\mu \mathrm{m}$-thick membrane.

Primary goal of the AEḡIS experiment is to precisely measure the free fall of antihydrogen within Earth’s gravitational field. To this end, cold (≈50 K) antihydrogen will traverse a two-grid moiré deflectometer before annihilating onto a position-sensitive detector, which shall determine the vertical position of the annihilation vertex relative to the grids with micrometric accuracy. Here, we introduce a vertexing detector based on a modified mobile camera sensor and experimentally demonstrate that it can measure the position of antiproton annihilations within 0.62 − 0.22 + 0.40 μm, a 35-fold improvement over the previous state of the art for real-time antiproton vertexing. These methods are directly applicable to antihydrogen. Moreover, the sensitivity to light of the sensor enables in situ calibration of the moiré deflectometer, substantially reducing systematic errors. This sensor emerges as a breakthrough technology toward the AEḡIS scientific goals and will constitute the basis for the development of a large-area detector for conducting antihydrogen gravity measurements.