Speaker
Description
Molecular hydrogen ions (MHIs) represent a class of bound quantum systems with significant potential for advancing our knowledge in multiple scientific domains, including the determination of fundamental constants, test of quantum physics, and the search for new interparticle forces. Furthermore, the comparison of transitions in MHIs and their antimatter counterparts provides an opportunity for novel tests of CPT invariance [1].
We have recently measured for the first time a Doppler-free rovibrational transition in a homonuclear MHI. Specifically, we studied an electric-quadrupole (E2) overtone rovibrational transition in H$_2^+$ [2]. We achieved an experimental fractional uncertainty of $8\times10^{-12}$. Our measured frequency is in agreement with the theoretical prediction. From the theoretical and experimental result, we deduced a value of the proton-to-electron mass ratio, which is in agreement with the CODATA 2022 value.
The already achieved experimental uncertainty stimulates us to consider seriously the vision of performing the spectroscopy with much higher accuracy first on H$_2^+$ and later on anti-H$_2^+$.
Myers [3] proposed performing laser vibrational spectroscopy of H$_2^+$ in a Penning trap with non-destructive read-out via the continuous Stern-Gerlach effect. This approach has recently been demonstrated in the ALPHATRAP facility (MPI-Kernphysik, Heidelberg) for the related molecular ion HD$^+$ [4,5].
We performed an extensive analysis of this proposal, and derived estimates for the achievable accuracy of the test [6]. We find that a comparison of the vibrational frequencies at a fractional level of $1\times10^{-17}$ is a realistic prospect, using technology that is mostly already available, particularly in the BASE-QLEDS trap [4,5,7,8].
We also analyzed complementary CPT invariance tests, namely those of the g-factor of the bound electron/positron via electron-spin-resonance spectroscopy and of the magnetic moment of the proton/antiproton via radiofrequency spectroscopy.
Acknowledgments: The work of S. S. performed under a grant of Deutsche Forschungsgemeinschaft includes a collaboration with S. Sturm and K. Blaum and their team on spectroscopy of HD$^+$ in ALPHATRAP. Joint discussions about spectroscopy in ALPHATRAP have been helpful.
The work of S. S. was performed under grant Schi 431/29-1 of Deutsche Forschungsgemeinschaft (DFG) and from both the DFG and the state of North-Rhine-Westphalia (Grant Nos. INST-208/774-1 FUGG and INST-208/796-1 FUGG). The work of S. S. and D. B. was also supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No. 786306, “PREMOL”). J. M. C. acknowledges the grant “RYC2023-042535-I” funded by MICIU/AEI/10.13039/501100011033 and by “ESF+”.
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