Effects of microwave leakage in caesium clocks: Theoretical and experimental results

We investigated the effects of microwave leakage fields in an atomic fountain clock. In a series of experiments a test microwave signal was beamed into the vacuum system with controlled amplitude, phase, and timing. The observed frequency shifts can be explained by a theoretical model based on an iterative solution of the Bloch equations up to second order. This model applies to both caesium fountain clocks and conventional thermal beam clocks and provides new and essential insights into the problem of microwave leakage fields.