Direct observation of transitions between quantum states with energy differences below 10 neV employing a Sona unit

Abstract

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 $$f \sim $$ 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 $$F=1$$ F = 1 and $$m_F = -1, 0, +1$$ m F = - 1 , 0 , + 1 of $$2S_{1/2}$$ 2 S 1 / 2 metastable hydrogen atoms as function of a magnetic field. Graphic Abstract