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Magnetically confined neutral antihydrogen atoms released in a gravity field were found to fall towards Earth like ordinary matter, in accordance with Einstein’s general theory of relativity.

Antihydrogen studies are important in testing the fundamental principles of physics but producing antihydrogen in large amounts is challenging. Here the authors demonstrate an efficient and high-precision method for trapping and stacking antihydrogen by using controlled plasma.

The ALPHA Collaboration reports measurements of the hyperfine components of the 1S–2S transition in trapped antihydrogen. They interpret the results as a test of the invariance of charge–parity–time-reversal symmetry.

The hyperfine splitting of antihydrogen has been measured and is consistent with expectations for atomic hydrogen.

Positrons are key to the production of cold antihydrogen. Here the authors report the sympathetic cooling of positrons by interacting them with laser-cooled Be⁺ ions resulting in a three-fold reduction of the temperature of positrons for antihydrogen synthesis.

One intriguing question about antimatter that is yet to be directly answered is whether or not it behaves exactly the same as matter under gravity. Here, a direct experimental method is presented to measure the ratio of inertial to gravitational mass for antihydrogen under free-fall conditions.

The successful laser cooling of trapped antihydrogen, the antimatter atom formed by an antiproton and a positron (anti-electron), is reported.

Fundamental theories do not predict a difference between the properties of matter and antimatter, but experimental tests of this are still in their infancy. To this end, this study analyses the effects of electric fields on antihydrogen atoms in the ALPHA trap to place a bound on the charge of antihydrogen.

Precision measurements of the 1S–2P transition in antihydrogen that take into account the standard Zeeman and hyperfine effects confirm the predictions of quantum electrodynamics.

The shape of the spectral line and the resonance frequency of the 1S–2S transition in antihydrogen agree very well with those of hydrogen.

Antihydrogen has been created, trapped and stored for 1,000 s. The improved holding time means that we now have access to the ground state of antimatter—long enough to test whether matter and antimatter obey the same physical laws.

The 1S–2S transition in magnetically trapped atoms of antihydrogen is observed, and its frequency is shown to be consistent with that expected for hydrogen.

These authors demonstrate resonant quantum transitions in a pure antimatter atom—antihydrogen—by using microwave radiation to flip the spin of the positron of an anti-atom in a magnetic trap, thus ejecting the anti-atom.

The observation of the 1S–2P Lyman-α transition in the antihydrogen atom, the antimatter counterpart of hydrogen, is reported.

Antihydrogen, the bound state of an antiproton and a positron, has been produced at low energies at CERN since 2002. It is of fundamental interest for testing the standard model of elementary particles and interactions. However, experiments so far have produced antihydrogen that is not confined, precluding detailed study of its structure. Here, trapping of antihydrogen atoms is demonstrated, opening the door to precision measurements on anti atoms.

Stochastic acceleration applied to 1,000 trapped antihydrogen atoms yields a 20-fold reduction of the experimental upper bound on the magnitude of the charge of antihydrogen, which is expected to be charge neutral.