Advances in the atomic fountain clock at SIOM

This work presents several advances in our 87Rb atomic fountain clock (AFC) at Shanghai Institute of Optics and Fine Mechanics (SIOM). We directly lock the local oscillator (LO) of AFC, and make some improvements on the physical system, including optimizing the coupling of microwave and adjusting down the working temperature of interrogation region, etc. A short-term fractional frequency stability of 2.7 × 10-13τ-1/2 is obtained by comparing the AFC with an H-maser. In accuracy evaluation of AFC, a self-comparison method is introduced, and an evaluation precision of 6 ×10-16 is obtained at the average time of 300 000 s. In addition, a GPS common view instrument is set up to compare AFC with frequency standards at other time-keeping laboratories.