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@ARTICLE{Engels:897325,
      author       = {Engels, Ralf and Büscher, Markus and Buske, Paul and Gan,
                      Yuchen and Grigoryev, Kirill and Hanhart, Christoph and
                      Huxold, Lukas and Kannis, Chrysovalantis and Lehrach,
                      Andreas and Soltner, Helmut and Verhoeven, Vincent},
      title        = {{D}irect observation of transitions between quantum states
                      with energy differences below 10 ne{V} employing a {S}ona
                      unit},
      journal      = {The European physical journal / D},
      volume       = {75},
      number       = {9},
      issn         = {1434-6079},
      address      = {Heidelberg},
      publisher    = {Springer},
      reportid     = {FZJ-2021-03731},
      pages        = {257},
      year         = {2021},
      abstract     = {The direct access to atomic transitions between close by
                      quantum states employing standard spectroscopic methods is
                      often limited by the size of the necessary radio-frequency
                      cavities. Here we report on a new tool for fundamental
                      spectroscopy measurements that can overcome this
                      shortcoming. For this, a Sona transition unit was used,
                      i.e., two opposed solenoidal coils that provide an
                      oscillating field in the rest frame of the through-going
                      atomic beam. In this way, we were able to control the
                      induced photon energy down to 10 neV or f∼ MHz. The
                      tuneable parameter is the velocity of the atomic beam. For
                      illustration of the method, we report a measurement of the
                      hyperfine splitting energies between the substates with F=1
                      and $m_F=−1,0,+1$ of $2S_1/2$ metastable hydrogen atoms as
                      function of a magnetic field.},
      cin          = {IKP-2 / PGI-6 / ZAT / JARA-FAME / IAS-4 / IKP-4 / ZEA-1},
      ddc          = {530},
      cid          = {I:(DE-Juel1)IKP-2-20111104 / I:(DE-Juel1)PGI-6-20110106 /
                      I:(DE-Juel1)ZAT-20090406 / $I:(DE-82)080023_20140620$ /
                      I:(DE-Juel1)IAS-4-20090406 / I:(DE-Juel1)IKP-4-20111104 /
                      I:(DE-Juel1)ZEA-1-20090406},
      pnm          = {612 - Cosmic Matter in the Laboratory (POF4-612) / 5111 -
                      Domain-Specific Simulation $\&$ Data Life Cycle Labs (SDLs)
                      and Research Groups (POF4-511) / ATHENA/HGF - ATHENA -
                      Accelerator Technology Helmholtz Infrastructure
                      $(Athena-HGF_2019_2022)$},
      pid          = {G:(DE-HGF)POF4-612 / G:(DE-HGF)POF4-5111 /
                      $G:(DE-HGF)Athena-HGF_2019_2022$},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000701695300001},
      doi          = {10.1140/epjd/s10053-021-00268-4},
      url          = {https://juser.fz-juelich.de/record/897325},
}