Accurate Evaluation of Microwave-Leakage-Induced Frequency Shifts in Fountain Clocks

Abstract

We report theoretical calculations of the transition probability errors introduced by microwave leakage in Cs fountain clocks, which will shift the clock frequency. The results show that the transition probability errors are affected by the Ramsey pulse amplitude, the relative phase between the Ramsey field and the leakage field, and the asymmetry of the leakage fields for the upward and downward passages. This effect is quite different for the leakage fields presenting below the Ramsey cavity and above the Ramsey cavity. The leakage-field-induced frequency shifts of the NIM5 fountain clock in different cases are measured. The results are consistent with the theoretical calculations, and give an accurate evaluation of the leakage-field-induced frequency shifts, as distinguished from other microwave-power-related effects for the first time.

First evaluation of the primary frequency standard NTSC-CsF2

“…Therefore, the microwaves in the state-selection cavity are turned off after the state-selection process to prevent microwave leakage from the cavity. The calculation of microwave leakage frequency shift involves two cases, namely leakage field presented above and below the cavity [42]. The leakage field influence can be calculated using the perturbation method.…”

Cold atom clocks and their applications in precision measurements*

“…The microwave-power related frequency shift is introduced by three possible sources: the microwave leakage, the microwave spectral impurity, and the Ramsey cavity distributed phase (DCP). [99,107] Besides a careful sealing of a Ramsey cavity with indium to reduce the microwave leaked out, a Mach-Zehner interferometric RF switch can be added in the microwave synthesizer chain to switch off the microwave when atoms are outside of the cavity. The relative phases of two Ramsey pulses can be measured with a triggered-phase transient analyzer to make sure that the phase disturbance due to the interferometric RF switch is negligible.…”

First accuracy evaluation of the NRC-FCs2 primary frequency standard

“…The measured tilt differences of −2.42( 14) mrad NE and −3.42 (16) mrad NW give velocities of −13.0 mm s −1 and −18.6 mm s −1 . Here, this implies that the fountain is tilted at −2.93 mrad and −4.36 mrad, with initial offsets of 1.79(20) mm and 2.63 (35) mm for normal operation. We note that, in general, this alignment procedure for normal operation, which varies initial position to maximize R1, does not necessarily yield a maximum of R1 versus fountain tilt at the angle that maximizes the number detected.…”

“…Therefore, we are only sensitive to microwave leakage occurring below the Ramsey cavity during the atoms' descent, where the atoms are not shielded from background microwaves. For this situation, the effect on the transition probability between clock states is given by [35][36][37]…”