Majorana transitions in an atomic fountain clock

Recently, we observed quasi-periodic frequency oscillations in CSF1, the first caesium fountain clock at Physikalisch-Technische Bundesanstalt in Braunschweig, Germany. These oscillations could be traced back to Majorana transitions taking place between the second Ramsey interaction and the fluorescence detection. Such transitions mix the Zeeman sublevels in a coherent way and therefore lead to additional contributions in the interference pattern. Combined with the unavoidable Δm = ±1 transitions inside the Ramsey cavity, frequency errors can arise when the overall symmetry with respect to ±m is broken in the detection zone because of an m-dependent detection efficiency. A change in field configuration eliminated the Majorana transitions and with it the frequency oscillations.