Journal Article

Observation of the hyperfine spectrum of antihydrogen

Gutierrez, A., Jonsell, S., Butler, E., Kurchaninov, L., Evetts, N., Capra, A., Carruth, C., Eriksson, S., Olin, A., Sarid, E., Isaac, C. A., Madsen, N., Thompson, J. E., Wurtele, J. S., Jones, S. A., Michan, J. M., Friesen, T., Ishida, A., Hardy, W. N., Nolan, P., Olchanski, K., Baker, C. J., Collister, R., Fajans, J., Gill, D. R., Tharp, T. D., Pusa, P., Silveira, D. M., Cohen, S., Stutter, G., Charlton, M., Munich, J. J., van der Werf, D. P., Ahmadi, M., Thompson, R. I., Mathers, M., Bertsche, W., Hayden, M. E., Sacramento, R. L., Cesar, C. L., Momose, T., Evans, A., Robicheaux, F., Rasmussen, C. Ø., Hangst, J. S., Fujiwara, M. C., So, C., Maxwell, D., Johnson, M. A., McKenna, J. T. K., Sameed, M., Menary, S., Stracka, S., Alves, B. X. R.

2017

Overview

The hyperfine splitting of antihydrogen has been measured and is consistent with expectations for atomic hydrogen. Assessing the antihydrogen spectrum Comparing precision measurements of hydrogen with equivalent measurements of antihydrogen is a way of testing charge–parity–time (CPT) symmetries, which are fundamental to physics. However, the fragility of antihydrogen makes it very difficult to produce in sufficient quantities to perform spectroscopic measurements. Here, the authors use a new antihydrogen accumulation technique, which allows for measuring the hyperfine spectrum of antihydrogen. The results reveal no differences between hydrogen and antihydrogen. As the spectrum of hydrogen is known very well and to high precision, experimental improvements could yield extremely precise tests of the CPT theorem. The observation of hyperfine structure in atomic hydrogen by Rabi and co-workers 1 , 2 , 3 and the measurement 4 of the zero-field ground-state splitting at the level of seven parts in 10 13 are important achievements of mid-twentieth-century physics. The work that led to these achievements also provided the first evidence for the anomalous magnetic moment of the electron 5 , 6 , 7 , 8 , inspired Schwinger’s relativistic theory of quantum electrodynamics 9 , 10 and gave rise to the hydrogen maser 11 , which is a critical component of modern navigation, geo-positioning and very-long-baseline interferometry systems. Research at the Antiproton Decelerator at CERN by the ALPHA collaboration extends these enquiries into the antimatter sector. Recently, tools have been developed that enable studies of the hyperfine structure of antihydrogen 12 —the antimatter counterpart of hydrogen. The goal of such studies is to search for any differences that might exist between this archetypal pair of atoms, and thereby to test the fundamental principles on which quantum field theory is constructed. Magnetic trapping of antihydrogen atoms 13 , 14 provides a means of studying them by combining electromagnetic interaction with detection techniques that are unique to antimatter 12 , 15 . Here we report the results of a microwave spectroscopy experiment in which we probe the response of antihydrogen over a controlled range of frequencies. The data reveal clear and distinct signatures of two allowed transitions, from which we obtain a direct, magnetic-field-independent measurement of the hyperfine splitting. From a set of trials involving 194 detected atoms, we determine a splitting of 1,420.4 ± 0.5 megahertz, consistent with expectations for atomic hydrogen at the level of four parts in 10 4 . This observation of the detailed behaviour of a quantum transition in an atom of antihydrogen exemplifies tests of fundamental symmetries such as charge–parity–time in antimatter, and the techniques developed here will enable more-precise such tests.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/766/36/1123 / 639/766/419/1131 / Antihydrogen / Antimatter / Antiparticles / Antiprotons / Atomic physics / Atomic structure / Cosmic rays / Critical components / Electromagnetic interactions / Experiments / General Physics / Humanities and Social Sciences / Hydrogen / Hyperfine structure / Interferometry / letter / Magnetic fields / Magnetic moments / Matter & antimatter / multidisciplinary / Multivariate analysis / Observations / Physics / Quantum electrodynamics / Quantum field theory / Quantum theory / Relativistic theory / Science / Spectroscopy / Spectrum analysis / Splitting / Very long base interferometry