Four ppm measurement of the antihydrogen ground-state hyperfine splitting

Abstract The hydrogen atom is a touchstone for the foundations, evolution and frontiers of quantum theory 1–9 . Key spectral lines of this atom have been determined to remarkable precision 10,11 . Our research focuses on the study of antihydrogen, the antimatter counterpart of hydrogen. We test fundamental symmetries of nature (such as simultaneous charge conjugation, parity inversion, and time reversal or CPT symmetry) through precision comparisons of these atomic systems 12 . Recent 1S–2S spectroscopic measurements on trapped antihydrogen have achieved relative precisions of parts per trillion (refs. 13,14 ). However, the ground-state hyperfine splitting, which is sensitive to the internal structure of the antiproton, has only been measured to 400 parts per million (ppm). Here we report a 4 ppm measurement of the antihydrogen ground-state hyperfine splitting energy a 1S , advancing the state-of-the-art precision 15 by two orders of magnitude. From microwave spectroscopy experiments with roughly 24,000 anti-atoms, we determine $${a}_{1{\rm{S}}}/h=\mathrm{1,420,404.8}\pm 1.1(\mathrm{stat.})\pm 5.6\,(\mathrm{sys.})\,\text{kHz}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>a</mml:mi> <mml:mrow> <mml:mn>1</mml:mn> <mml:mi>S</mml:mi> </mml:mrow> </mml:msub> <mml:mo>/</mml:mo> <mml:mi>h</mml:mi> <mml:mo>=</mml:mo> <mml:mn>1,420,404.8</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1.1</mml:mn> <mml:mo>(</mml:mo> <mml:mi>stat.</mml:mi> <mml:mo>)</mml:mo> <mml:mo>±</mml:mo> <mml:mn>5.6</mml:mn> <mml:mspace/> <mml:mo>(</mml:mo> <mml:mi>sys.</mml:mi> <mml:mo>)</mml:mo> <mml:mspace/> <mml:mtext>kHz</mml:mtext> </mml:math> in a 1-T magnetic field, consistent with expectations for hydrogen 11 . At this level, our measurement is sensitive to the internal structure of the antiproton, which contributes at about 40 ppm and is approaching the limit of existing theoretical analyses 16 . The gains we report are the product of marked advances in magnetic trap field control, stabilization and characterization; anti-atom spin-state manipulation; and improved antihydrogen accumulation rate 17 .

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Nature
Published
2026-05-27
DOI
https://doi.org/10.1038/s41586-026-10556-x
Primary Topic
Atomic and Molecular Physics
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article
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article

Four ppm measurement of the antihydrogen ground-state hyperfine splitting

A. Capra, J. S. Wurtele, C. A. Isaac, A. N. Oliveira et al.
Nature
Atomic and Molecular Physics
article

Four ppm measurement of the antihydrogen ground-state hyperfine splitting

A. Capra, J. S. Wurtele, C. A. Isaac, A. N. Oliveira, P. Heidari, J. Suh, W. Bertsche, T. D. Tharp, A. Evans, M. Charlton, R. I. Thompson, T. Friesen, M. C. Fujiwara, D. Hodgkinson, J. FAJANS, C. L. Cesar, C. J. Baker, N. M. Bhatt, R. Akbari, T. Momose, J. S. Hangst, N. Madsen, J. Schoonwater, K. A. Thompson, M. B. Gomes Gonçalves, G. Smith, A. Powell, A. Del Vincio, A. G. Swadling, V. R. Marshall, C. Ø. Rasmussen, S. Stracka, D P van der Werf, S Eriksson, S. A. Jones, S. Jonsell, I. Carli, A. Cridland Mathad, S. G. Wilson, G. Bonomi, J. Nauta, D. Duque Quiceno, T. Robertson-Brown, F. Robicheaux, J. Singh, D. M. Silveira, R. L. Sacramento, J. T. K. McKenna, E. Thorpe-Woods, E. Sarid, A. J. Uribe Jimenez, L. M. Golino, M. Urioni, C. So, M. E. Hayden, L. O. de Araujo Azevedo, P. Woosaree
article en

Abstract

Abstract The hydrogen atom is a touchstone for the foundations, evolution and frontiers of quantum theory 1–9 . Key spectral lines of this atom have been determined to remarkable precision 10,11 . Our research focuses on the study of antihydrogen, the antimatter counterpart of hydrogen. We test fundamental symmetries of nature (such as simultaneous charge conjugation, parity inversion, and time reversal or CPT symmetry) through precision comparisons of these atomic systems 12 . Recent 1S–2S spectroscopic measurements on trapped antihydrogen have achieved relative precisions of parts per trillion (refs. 13,14 ). However, the ground-state hyperfine splitting, which is sensitive to the internal structure of the antiproton, has only been measured to 400 parts per million (ppm). Here we report a 4 ppm measurement of the antihydrogen ground-state hyperfine splitting energy a 1S , advancing the state-of-the-art precision 15 by two orders of magnitude. From microwave spectroscopy experiments with roughly 24,000 anti-atoms, we determine $${a}_{1{\rm{S}}}/h=\mathrm{1,420,404.8}\pm 1.1(\mathrm{stat.})\pm 5.6\,(\mathrm{sys.})\,\text{kHz}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>a</mml:mi> <mml:mrow> <mml:mn>1</mml:mn> <mml:mi>S</mml:mi> </mml:mrow> </mml:msub> <mml:mo>/</mml:mo> <mml:mi>h</mml:mi> <mml:mo>=</mml:mo> <mml:mn>1,420,404.8</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1.1</mml:mn> <mml:mo>(</mml:mo> <mml:mi>stat.</mml:mi> <mml:mo>)</mml:mo> <mml:mo>±</mml:mo> <mml:mn>5.6</mml:mn> <mml:mspace/> <mml:mo>(</mml:mo> <mml:mi>sys.</mml:mi> <mml:mo>)</mml:mo> <mml:mspace/> <mml:mtext>kHz</mml:mtext> </mml:math> in a 1-T magnetic field, consistent with expectations for hydrogen 11 . At this level, our measurement is sensitive to the internal structure of the antiproton, which contributes at about 40 ppm and is approaching the limit of existing theoretical analyses 16 . The gains we report are the product of marked advances in magnetic trap field control, stabilization and characterization; anti-atom spin-state manipulation; and improved antihydrogen accumulation rate 17 .

NatureVol. 653(8116)
Marquette University (US), Universidade Federal do Rio de Janeiro (BR), Ben-Gurion University of the Negev (IL), TRIUMF (CA), High Energy Accelerator Research Organization (JP), University of British Columbia (CA), Stockholm University (SE), University of Calgary (CA), University of Groningen (NL), Simon Fraser University (CA), Cockcroft Institute (GB), University of Trento (IT), Brookhaven National Laboratory (US), Aarhus University (DK), Purdue University West Lafayette (US), University of Manchester (GB), Swansea University (GB), Sci-Tech Daresbury (GB), Istituto Nazionale di Fisica Nucleare, Sezione di Pavia (IT), Istituto Nazionale di Fisica Nucleare, Sezione di Pisa (IT), European Organization for Nuclear Research (CH), University of Brescia (IT), University of California, Berkeley (US)
National Science Foundation, U.S. Department of Energy, TRIUMF, CERN, Leverhulme Trust, Conselho Nacional de Desenvolvimento Científico e Tecnológico, Israel Science Foundation, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Natural Sciences and Engineering Research Council of Canada, Engineering and Physical Sciences Research Council, Science and Technology Facilities Council
Openalex Percentile: Top 6%
Atomic and Molecular Physics
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