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The magnetic moment of the antiproton is measured at the parts-per-billion level, improving on previous measurements by a factor of about 350.

High-precision measurements could disclose fundamental dissimilarities between matter and antimatter, which are found imbalanced in the Universe. Here, the authors measure the magnetic moment of the antiproton with six-fold higher accuracy than before, finding it consistent with that of the proton.

Spin-flip resonance data are used to place direct constraints on the interaction of ultralight axion-like particles with antiprotons, improving the sensitivity to the corresponding coupling coefficient by five orders of magnitude.

The successful transport of a trapped proton cloud from the antimatter factory of CERN using a transportable, superconducting, autonomous and open Penning-trap system that can distribute antiprotons into other experiments is reported.

Coherent quantum transition spectroscopy of the spin of a single antiproton is reported, demonstrating Rabi oscillations of the spin and enabling improved measurement of matter/antimatter symmetry using proton and antiproton magnetic moments.

The magnetic moment of the proton is directly measured with unprecedented precision using a double Penning trap.

The CPT theorem (the assumption that physical laws are invariant under simultaneous charge conjugation, parity transformation and time reversal) is central to the standard model of particle physics; here the charge-to-mass ratio of the antiproton is compared to that of the proton, with a precision of 69 parts per trillion, and the result supports the CPT theorem at the atto-electronvolt scale.

Multiple high-precision measurement campaigns at CERN of the antiproton-to-proton charge-to-mass ratio—to a precision of 16 parts per trillion—in a cryogenic multi-Penning trap offer no evidence of charge–parity–time violation, and set stringent limits on the clock-weak-equivalence principle.

A single electromagnetically trapped proton is sympathetically cooled to below ambient temperature by coupling it through a superconducting LC circuit to a laser-cooled cloud of Be⁺ ions stored in a spatially separated trap.