Characterization of the 1S–2S transition in antihydrogen
2018
In 1928, Dirac published an equation 1 that combined quantum mechanics and
special relativity.
Negative-energysolutions to this equation, rather than being unphysical as initially thought, represented a class of hitherto unobserved and unimagined particles—
antimatter. The existence of particles of
antimatterwas confirmed with the discovery of the positron 2 (or anti-electron) by Anderson in 1932, but it is still unknown why matter, rather than
antimatter, survived after the
Big Bang. As a result, experimental studies of antimatter3–7, including tests of fundamental symmetries such as charge–parity and charge–parity–time, and searches for evidence of primordial
antimatter, such as antihelium nuclei, have high priority in contemporary physics research. The fundamental role of the hydrogen atom in the evolution of the Universe and in the historical development of our understanding of quantum physics makes its
antimattercounterpart—the
antihydrogenatom—of particular interest. Current standard-model physics requires that hydrogen and
antihydrogenhave the same energy levels and
spectral lines. The laser-driven 1S–2S transition was recently observed 8 in
antihydrogen. Here we characterize one of the hyperfine components of this transition using
magnetically trappedatoms of
antihydrogenand compare it to model calculations for hydrogen in our apparatus. We find that the shape of the
spectral lineagrees very well with that expected for hydrogen and that the resonance frequency agrees with that in hydrogen to about 5 kilohertz out of 2.5 × 1015
hertz. This is consistent with charge–parity–time invariance at a relative precision of 2 × 10−12—two orders of magnitude more precise than the previous determination 8 —corresponding to an absolute energy sensitivity of 2 × 10−20 GeV.
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