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Baker CJ, Bertsche W, Capra A, Carruth C, Cesar CL, Charlton M, Christensen A, Collister R, Mathad AC, Eriksson S, Evans A, Evetts N, Fajans J, Friesen T, Fujiwara MC, Gill DR, Grandemange P, Granum P, Hangst JS, Hardy WN, Hayden ME, Hodgkinson D, Hunter E, Isaac CA, Johnson MA, Jones JM, Jones SA, Jonsell S, Khramov A, Knapp P, Kurchaninov L, Madsen N, Maxwell D, McKenna JTK, Menary S, Michan JM, Momose T, Mullan PS, Munich JJ, Olchanski K, Olin A, Peszka J, Powell A, Pusa P, Rasmussen CØ, Robicheaux F, Sacramento RL, Sameed M, Sarid E, Silveira DM, Starko DM, So C, Stutter G, Tharp TD, Thibeault A, Thompson RI, van der Werf DP, Wurtele JS. Laser cooling of antihydrogen atoms. Nature 2021; 592:35-42. [PMID: 33790445 PMCID: PMC8012212 DOI: 10.1038/s41586-021-03289-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Accepted: 01/26/2021] [Indexed: 11/08/2022]
Abstract
The photon-the quantum excitation of the electromagnetic field-is massless but carries momentum. A photon can therefore exert a force on an object upon collision1. Slowing the translational motion of atoms and ions by application of such a force2,3, known as laser cooling, was first demonstrated 40 years ago4,5. It revolutionized atomic physics over the following decades6-8, and it is now a workhorse in many fields, including studies on quantum degenerate gases, quantum information, atomic clocks and tests of fundamental physics. However, this technique has not yet been applied to antimatter. Here we demonstrate laser cooling of antihydrogen9, the antimatter atom consisting of an antiproton and a positron. By exciting the 1S-2P transition in antihydrogen with pulsed, narrow-linewidth, Lyman-α laser radiation10,11, we Doppler-cool a sample of magnetically trapped antihydrogen. Although we apply laser cooling in only one dimension, the trap couples the longitudinal and transverse motions of the anti-atoms, leading to cooling in all three dimensions. We observe a reduction in the median transverse energy by more than an order of magnitude-with a substantial fraction of the anti-atoms attaining submicroelectronvolt transverse kinetic energies. We also report the observation of the laser-driven 1S-2S transition in samples of laser-cooled antihydrogen atoms. The observed spectral line is approximately four times narrower than that obtained without laser cooling. The demonstration of laser cooling and its immediate application has far-reaching implications for antimatter studies. A more localized, denser and colder sample of antihydrogen will drastically improve spectroscopic11-13 and gravitational14 studies of antihydrogen in ongoing experiments. Furthermore, the demonstrated ability to manipulate the motion of antimatter atoms by laser light will potentially provide ground-breaking opportunities for future experiments, such as anti-atomic fountains, anti-atom interferometry and the creation of antimatter molecules.
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Affiliation(s)
- C J Baker
- Department of Physics, College of Science, Swansea University, Swansea, UK
| | - W Bertsche
- School of Physics and Astronomy, University of Manchester, Manchester, UK
- Cockcroft Institute, Sci-Tech Daresbury, Warrington, UK
| | - A Capra
- TRIUMF, Vancouver, British Columbia, Canada
| | - C Carruth
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
| | - C L Cesar
- Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - M Charlton
- Department of Physics, College of Science, Swansea University, Swansea, UK
| | - A Christensen
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
| | | | - A Cridland Mathad
- Department of Physics, College of Science, Swansea University, Swansea, UK
| | - S Eriksson
- Department of Physics, College of Science, Swansea University, Swansea, UK
| | - A Evans
- Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
| | - N Evetts
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada
| | - J Fajans
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
| | - T Friesen
- Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
| | | | - D R Gill
- TRIUMF, Vancouver, British Columbia, Canada
| | - P Grandemange
- TRIUMF, Vancouver, British Columbia, Canada
- Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
| | - P Granum
- Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
| | - J S Hangst
- Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark.
| | - W N Hardy
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada
| | - M E Hayden
- Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada
| | - D Hodgkinson
- School of Physics and Astronomy, University of Manchester, Manchester, UK
| | - E Hunter
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
| | - C A Isaac
- Department of Physics, College of Science, Swansea University, Swansea, UK
| | - M A Johnson
- School of Physics and Astronomy, University of Manchester, Manchester, UK
- Cockcroft Institute, Sci-Tech Daresbury, Warrington, UK
| | - J M Jones
- Department of Physics, College of Science, Swansea University, Swansea, UK
| | - S A Jones
- Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
| | - S Jonsell
- Department of Physics, Stockholm University, Stockholm, Sweden
| | - A Khramov
- TRIUMF, Vancouver, British Columbia, Canada
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Physics, British Columbia Institute of Technology, Burnaby, British Columbia, Canada
| | - P Knapp
- Department of Physics, College of Science, Swansea University, Swansea, UK
| | | | - N Madsen
- Department of Physics, College of Science, Swansea University, Swansea, UK
| | - D Maxwell
- Department of Physics, College of Science, Swansea University, Swansea, UK
| | - J T K McKenna
- TRIUMF, Vancouver, British Columbia, Canada
- Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
| | - S Menary
- Department of Physics and Astronomy, York University, Toronto, Ontario, Canada
| | - J M Michan
- TRIUMF, Vancouver, British Columbia, Canada
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada
| | - T Momose
- TRIUMF, Vancouver, British Columbia, Canada.
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada.
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada.
| | - P S Mullan
- Department of Physics, College of Science, Swansea University, Swansea, UK
| | - J J Munich
- Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada
| | | | - A Olin
- TRIUMF, Vancouver, British Columbia, Canada
- Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, Canada
| | - J Peszka
- Department of Physics, College of Science, Swansea University, Swansea, UK
| | - A Powell
- Department of Physics, College of Science, Swansea University, Swansea, UK
- Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
| | - P Pusa
- Department of Physics, University of Liverpool, Liverpool, UK
| | - C Ø Rasmussen
- Experimental Physics Department, CERN, Geneva, Switzerland
| | - F Robicheaux
- Department of Physics and Astronomy, Purdue University, West Lafayette, IN, USA
| | - R L Sacramento
- Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - M Sameed
- School of Physics and Astronomy, University of Manchester, Manchester, UK
| | - E Sarid
- Soreq NRC, Yavne, Israel
- Department of Physics, Ben Gurion University, Beer Sheva, Israel
| | - D M Silveira
- TRIUMF, Vancouver, British Columbia, Canada
- Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - D M Starko
- Department of Physics and Astronomy, York University, Toronto, Ontario, Canada
| | - C So
- TRIUMF, Vancouver, British Columbia, Canada
| | - G Stutter
- Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
| | - T D Tharp
- Physics Department, Marquette University, Milwaukee, WI, USA
| | - A Thibeault
- TRIUMF, Vancouver, British Columbia, Canada
- Faculté de Génie, Université de Sherbrooke, Sherbrooke, Quebec, Canada
| | - R I Thompson
- TRIUMF, Vancouver, British Columbia, Canada
- Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
| | - D P van der Werf
- Department of Physics, College of Science, Swansea University, Swansea, UK
| | - J S Wurtele
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
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Ahmadi M, Alves BXR, Baker CJ, Bertsche W, Capra A, Carruth C, Cesar CL, Charlton M, Cohen S, Collister R, Eriksson S, Evans A, Evetts N, Fajans J, Friesen T, Fujiwara MC, Gill DR, Granum P, Hangst JS, Hardy WN, Hayden ME, Hunter ED, Isaac CA, Johnson MA, Jones JM, Jones SA, Jonsell S, Khramov A, Knapp P, Kurchaninov L, Madsen N, Maxwell D, McKenna JTK, Menary S, Michan JM, Momose T, Munich JJ, Olchanski K, Olin A, Pusa P, Rasmussen CØ, Robicheaux F, Sacramento RL, Sameed M, Sarid E, Silveira DM, So C, Starko DM, Stutter G, Tharp TD, Thompson RI, van der Werf DP, Wurtele JS. Investigation of the fine structure of antihydrogen. Nature 2020; 578:375-380. [PMID: 32076225 PMCID: PMC7162817 DOI: 10.1038/s41586-020-2006-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Accepted: 12/20/2019] [Indexed: 10/29/2022]
Abstract
At the historic Shelter Island Conference on the Foundations of Quantum Mechanics in 1947, Willis Lamb reported an unexpected feature in the fine structure of atomic hydrogen: a separation of the 2S1/2 and 2P1/2 states1. The observation of this separation, now known as the Lamb shift, marked an important event in the evolution of modern physics, inspiring others to develop the theory of quantum electrodynamics2-5. Quantum electrodynamics also describes antimatter, but it has only recently become possible to synthesize and trap atomic antimatter to probe its structure. Mirroring the historical development of quantum atomic physics in the twentieth century, modern measurements on anti-atoms represent a unique approach for testing quantum electrodynamics and the foundational symmetries of the standard model. Here we report measurements of the fine structure in the n = 2 states of antihydrogen, the antimatter counterpart of the hydrogen atom. Using optical excitation of the 1S-2P Lyman-α transitions in antihydrogen6, we determine their frequencies in a magnetic field of 1 tesla to a precision of 16 parts per billion. Assuming the standard Zeeman and hyperfine interactions, we infer the zero-field fine-structure splitting (2P1/2-2P3/2) in antihydrogen. The resulting value is consistent with the predictions of quantum electrodynamics to a precision of 2 per cent. Using our previously measured value of the 1S-2S transition frequency6,7, we find that the classic Lamb shift in antihydrogen (2S1/2-2P1/2 splitting at zero field) is consistent with theory at a level of 11 per cent. Our observations represent an important step towards precision measurements of the fine structure and the Lamb shift in the antihydrogen spectrum as tests of the charge-parity-time symmetry8 and towards the determination of other fundamental quantities, such as the antiproton charge radius9,10, in this antimatter system.
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