https://doi.org/10.1140/epjd/s10053-021-00268-4
Regular Article - Atomic Physics
Direct observation of transitions between quantum states with energy differences below 10 neV employing a Sona unit
1
Institut für Kernphysik, Forschungszentrum Jülich, Jülich, Germany
2
Peter-Grünberg Institut, Forschungszentrum Jülich, Jülich, Germany
3
Institut für Laser- und Plasmaphysik, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany
4
Institute for Advanced Simulation, Forschungszentrum Jülich, Jülich, Germany
5
III. Physikalisches Institut B, RWTH Aachen University, Aachen, Germany
6
JARA-Fame, Forschungszentrum Jülich and RWTH Aachen University, Aachen, Germany
7
Zentralinstitut für Engineering, Elektronik und Analytik, Forschungszentrum Jülich, Jülich, Germany
8
Lehrstuhl für Technologie Optischer Systeme, RWTH Aachen University, Aachen, Germany
Received:
17
June
2021
Accepted:
6
September
2021
Published online:
29
September
2021
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 
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 
and 
of 
metastable hydrogen atoms as function of a magnetic field.
© The Author(s) 2021
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