Antihydrogen, a positron bound to an antiproton, is the simplest antiatom. Its counterpart—hydrogen—is one of the most precisely investigated and best understood systems in physics research. High-resolution comparisons of both systems provide sensitive tests of CPT symmetry, which is the most fundamental symmetry in the Standard Model of elementary particle physics. Any measured difference would point to CPT violation and thus to new physics. Here we report the development of an antihydrogen source using a cusp trap for in-flight spectroscopy. A total of 80 antihydrogen atoms are unambiguously detected 2.7 m downstream of the production region, where perturbing residual magnetic fields are small. This is a major step towards precision spectroscopy of the ground-state hyperfine splitting of antihydrogen using Rabi-like beam spectroscopy.

The authors have developed a method to produce a microbeam of slow highly charged ions based on a self-organized charge-up inside a tapered glass capillary. A transmission of $8\mathrm{keV}$ ${\mathrm{Ar}}^{8+}$ beam through the capillary $5\mathrm{cm}$ long with $800∕24\mu \mathrm{m}$ inlet/outlet inner diameters was observed stably for more than $1200\mathrm{s}$ . The transmitted beam had the same size as the outlet with a beam density enhancement of approximately 10 and a divergence of $\pm 5\mathrm{mrad}$ . The initial beam was guided through a capillary tilted by as large as $\pm 100\mathrm{mrad}$ , and it still kept the incident charge.

Invariance under the charge, parity, time-reversal (CPT) transformation¹ is one of the fundamental symmetries of the standard model of particle physics. This CPT invariance implies that the fundamental properties of antiparticles and their matter-conjugates are identical, apart from signs. There is a deep link between CPT invariance and Lorentz symmetry—that is, the laws of nature seem to be invariant under the symmetry transformation of spacetime—although it is model dependent². A number of high-precision CPT and Lorentz invariance tests—using a co-magnetometer, a torsion pendulum and a maser, among others—have been performed³, but only a few direct high-precision CPT tests that compare the fundamental properties of matter and antimatter are available^4,5,6,7,8. Here we report high-precision cyclotron frequency comparisons of a single antiproton and a negatively charged hydrogen ion (H⁻) carried out in a Penning trap system. From 13,000 frequency measurements we compare the charge-to-mass ratio for the antiproton to that for the proton and obtain . The measurements were performed at cyclotron frequencies of 29.6 megahertz, so our result shows that the CPT theorem holds at the atto-electronvolt scale. Our precision of 69 parts per trillion exceeds the energy resolution of previous antiproton-to-proton mass comparisons^7,9 as well as the respective figure of merit of the standard model extension¹⁰ by a factor of four. In addition, we give a limit on sidereal variations in the measured ratio of <720 parts per trillion. By following the arguments of ref. 11, our result can be interpreted as a stringent test of the weak equivalence principle of general relativity using baryonic antimatter, and it sets a new limit on the gravitational anomaly parameter of < 8.7 × 10⁻⁷.