Swansea University physicists, as leading members of the ALPHA collaboration
at CERN, have demonstrated laser cooling of antihydrogen atoms for the first
time. The groundbreaking achievement produces colder antimatter than ever
before and enables an entirely new class of experiments, helping scientists
learn more about antimatter in future.
In a paper published today in Nature, the collaboration reports that the
temperature of antihydrogen atoms trapped inside a magnetic bottle is
reduced when the atoms scatter light from an ultraviolet laser beam, slowing
the atoms down and reducing the space they occupy in the bottle -- both
vital aspects of future more detailed studies of the properties of
antimatter.
In addition to showing that the energy of the antihydrogen atoms was
decreased, the physicists also found a reduction in the range of wavelengths
that the cold atoms can absorb or emit light on, so the spectral line (or
colour band) is narrowed due to the reduced motion.
This latter effect is of particular interest, as it will allow a more
precise determination of the spectrum which in turn reveals the internal
structure of the antihydrogen atoms.
Antimatter is a necessity in the most successful quantum mechanical models
of particle physics. It became available in the laboratory nearly a century
ago with the discovery of the positively charged positron, the antimatter
counterpart of the negatively charged electron.
When matter and antimatter come together annihilation occurs; a striking
effect wherein the original particles disappear. Annihilation can be
observed in the laboratory and is even used in medical diagnostic techniques
such as positron emission tomography (PET) scans. However, antimatter
presents a conundrum. An equal amount of antimatter and matter formed in the
Big Bang, but this symmetry is not preserved today as antimatter seems to be
virtually absent from the visible universe.
Swansea University's Professor Niels Madsen, who was responsible for the
experimental run, said: "Since there is no antihydrogen around, we have to
make it in the lab at CERN. It's a remarkable feat that we can now also
laser-cool antihydrogen and make a very precise spectroscopic measurement,
all in less than a single day. Only two years ago, the spectroscopy alone
would take ten weeks. Our goal is to investigate if the properties of our
antihydrogen match those of ordinary hydrogen as expected by symmetry. A
difference, however small, could help explain the some of the deep questions
surrounding antimatter."
Professor Eriksson, who was responsible for the spectroscopy lasers involved
in the study, said: "This spectacular result takes antihydrogen research to
the next level, as the improved precision that laser cooling brings puts us
in contention with experiments on normal matter. This is a tall order since
the spectrum of hydrogen that we compare with has been measured with a
staggering precision of fifteen digits. We are already upgrading our
experiment to meet the challenge!"
Reference:
Baker, C.J., Bertsche, W., Capra, A. et al. Laser cooling of antihydrogen
atoms. Nature 592, 35–42 (2021).
DOI:
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