—Two 171 Yb + single-ion optical frequency standards operating at 688 THz (436 nm) are compared in order to investigate systematic frequency shifts in the subhertz range. In the absence of externally applied perturbations, a mean relative frequency difference of 3.8 · 10 −16 is observed. Using a femtosecond frequency comb generator based on an Er 3+-doped… (More)
—We stabilize a microwave oscillator at 9.6 GHz to an optical clock laser at 344 THz by using a fiber-based femto-second laser frequency comb as a transfer oscillator. With a second frequency comb, we independently measure the instability of the microwave source with respect to another optical clock laser frequency at 456 THz. The total fractional frequency… (More)
Coherent manipulation of atomic states is a key concept in high-precision spectroscopy and used in atomic fountain clocks and a number of optical frequency standards. Operation of these standards can involve a number of cyclic switching processes, which may induce cycle-synchronous phase excursions of the interrogation signal and thus lead to shifts in the… (More)
—We explore the method of rapid adiabatic passage for collisional frequency shift measurements in the primary caesium fountain clock PTB-CSF2 at the Physikalisch-Technische Bundesanstalt (PTB). This method can be used to vary the local density distribution of the atom cloud by exactly a factor of 2. We investigate the performance of the method for different… (More)
—Recently, we observed quasi-periodic frequency oscillations in CSF1, which is the first cesium fountain clock at These oscillations could be traced back to Majorana transitions after the second Ramsey interaction. A change in field configuration eliminated the Majorana transitions and with it the frequency oscillations.