Progress on the 40Ca+ ion optical clock

Progress of the(40)Ca(+)ion optical clock based on the 4(2)S(1/2)- 3d(2)D(5/2)electric quadrupole transition is reported. By setting the drive frequency to the magic frequency omega(0), the frequency uncertainty caused by the scalar Stark shift and second-order Doppler shift induced by micromotion is reduced to the 10(-19)level. By precisely measuring the differential static scalar polarizability Delta alpha(0), the uncertainty due to the blackbody radiation (BBR) shift (coefficient) is reduced to the 10(-19)level. With the help of a second-order integrating servo algorithm, the uncertainty due to the servo error is reduced to the 10(-18)level. The total fractional uncertainty of the(40)Ca(+)ion optical clock is then improved to 2.2x 10(-17), whereas this value is mainly restricted by the uncertainty of the BBR shift due to temperature fluctuations. The state preparation is introduced together with improvements in the pulse sequence, and furthermore, a better signal to noise ratio (SNR) and less dead time are achieved. The clock stability of a single clock is improved to4.8x10-15/tau(inseconds)