Modulation-induced frequency shifts in a coherent-population-trapping-based atomic clock

We investigate systematic errors associated with a common modulation technique used for phase-sensitive detection of a coherent-population-trapping (CPT) resonance. In particular, we show that modification of the CPT resonance line shape due to the presence of off-resonant fields leads to frequency shifts that may limit the stability of CPT-based atomic clocks. We also demonstrate that an alternative demodulation technique greatly reduces these effects.