Frequency metrology for precision measurements on matter-antimatter symmetry

The virtual absence of antimatter and preponderance of matter in the Universe today remains one of the biggest conundrums facing physics. Already in 1967, the famous Sakharov conditions described how this asymmetric Universe could come about by requiring symmetry violations (i.e. differences) between matter and antimatter. Until now, no sufficient symmetry violations have been found to resolve this question, thus the puzzle remains. This project aims to seek answers to this question by directly testing the supposition that the structure of atoms made of antimatter is indistinguishable from the structure in their matter counterparts. This grant proposes the installation of a caesium fountain atomic clock which will allow spectroscopic measurements of antihydrogen with an uncertainty commensurate with how accurately we can measure time itself. This project provides state-of-the-art equipment for our long-term programme where we use this ultimate tool of precision measurements to address the antimatter conundrum. Our approach is to trap antihydrogen atoms, (atoms that we make by combining antiprotons and positrons) in order to study their internal structure using spectroscopic techniques from atomic physics. We draw from work that have given us the most precise gauges in the scientific toolbox to date and the basis for the global positioning system (GPS); atomic clocks. Specifically, we investigate the ground to first excited state transition in antihydrogen (antimatter) held in a magnetic trap to test the hypothesis that the frequency of this transition is exactly the same as that of hydrogen (matter). This transition has been investigated with a staggering 15 decimal places of precision in hydrogen. We have recently achieved a precision of 12 decimal places in antihydrogen. Improving our antimatter-work to match the result in matter experiments requires us to determine the antihydrogen 1S-2S transition frequency with the accuracy of the corresponding measurement in hydrogen. The new equipment is a state-of-the-art atomic clock identical to the type that makes the definition of the SI-second practical. Since the atomic clock directly measures the hyperfine interval in caesium as defined in the SI-system of units, it will give us the best possible absolute frequency reference and allow us to reach the precision achieved in matter with antimatter. The antimatter research that this project enables , tests the very foundations of physics that explains the world around us and forms the basis technology of increasing complexity. Despite all this success, we still do not understand why there appears to be no bulk antimatter in the Universe. In this project we look for tiny deviations from expectations based on our current understanding. Experience shows that precise observation of Nature leads to breakthroughs in our understanding. Here, antihydrogen is a compelling subject due to the very specific predictions of its properties, and the already available precise results in its matter counterpart. The risk of finding no new clues on this path is far outweighed by the risk of not looking for them when we now very clearly can. An observed difference between antihydrogen and hydrogen that can be attributed to symmetry breaking would have profound, today even unimaginable, consequences on the foundations of physics. Even if no clues are found now, there is immense intrinsic value in the most precise direct measurement of a property in antihydrogen.