The Experimental Research Of ⁴⁰Ca⁺ Optical Frequency Standards With 10^-17 Level Uncertainty And Stability

As one kind of precise timekeeping instrument,atomic clock has important applications in the fields of navigation,time distribution and the network synchronization.The optical frequency standard has better stability and accuracy own to its high transition frequency and it is promising as the next generation of the standard of time and frequency.The lifetime of 3 D5/2 for calcium ion is about 1 second and the corresponding natural linewidth of 4 S1/2 to 3 D5/2 is about 0.16 Hertz.This transition has a quality factor of 1015 and it's very appropriate as the reference transition of the optical frequency standard.The optical clock based on the 40Ca+single-ion has the advantage of simple construction and low cost and its accuracy has the potential to surpass the Cs fountains clocks.Based on the previous platforms,we carry on the comparison experiment of two 40Ca+single-ion optical clocks.The main contents are categorized as follows:1.We stabilize a 729 nm Ti:sapphire laser to a 10 cm long ULE ultra-stable optical reference cavity by means of Pound-Drever-Hall method.By the optimization of stability of vibration,temperature stability and locking electronics,the Ti:sapphire laser has a 1 Hertz linewidth by beating with another narrow linewidth diode laser.The Allan deviation of the beatnote is better than 2×1015 at the timescales of 1-100 s.2.The trapping electronical field of trap2 is renovated and the RF frequency is set to be 24.7 MHz.One single ion can be stored in the trap stably and the micromotion is minimized.Because the second order Doppler and stark shift is anticorrelation,the shift from the micromotion is suppressed to a high level by operating the trap2 at a special RF frequency.3.The frequency comparison experiment of two identical two 40Ca+ single-ion optical clocks is carried on.The shifts which are derived from blackbody radiation,micromotion,secular motion and so on are evaluated carefully.The results show that the frequency difference between the two clocks is measared to be 3.2 ×10-17 with a measurement uncertainty of 5.5 × 10-17,considering both the statistic(1.9 × 10-17)and the systematic(5.1×10-17)uncertainties.4.The long term frequency stabilization of the cooling laser and repumping laser are enhanced by Pound-Drever-Hall method.The linewidth of both lasers are less than 1 MHz and the lasers stays locked to the reference cavity for more than one week.This improvement lays a solid foundation for the optical clock which has a 10'18 level accuracy.