Two Methods About C-field Evaluation in Beam Clock

SummaryTwo new methods related to the evaluation of thermal beam clock's C-field are presented and experiments are shown. The first method measures the stability of C-field locking by using 1-1 line to lock the microwave frequency and 0-0 line to lock the C-field. As the 1-1 line is more sensitive to the magnetic field, such locking makes it easily to see the magnetic field fluctuations after locking. The second method uses a large modulation depth of the microwave frequency locking, so that the frequency points are in the left and right of the Rabi resonance curve instead of the Ramsey fringes. Using this method, we measure the deviation of the center of the Rabi and Ramsey resonance curve, which can evaluate the inhomogeneity of the C-field.

I. Introduction

Compared to laboratory clocks, compact clocks are used in more complex and variable environments with different temperature, air pressure, magnetic fields and so on. C-fields may deviate from the value at the time of assembly and may also vary over time. Although these problems can be partially solved with sophisticated simulations, efficient magnetic shielding, and high precision current control, sensitive atoms can still sense very weak C-field variations.