Optical clocks have been demonstrated to be good choices to redefine the SI “second.” With this goal, we have constructed a quantum-logic-based 27Al+ ion optical clock with a fractional frequency uncertainty of 1.6×10−18. A 25Mg+ ion is used as the logic ion for sympathetic cooling, state readout, and frequency-shift measurement of the 27Al+ ion. The stability of the optical clock is 2.6×10-15/√τ , measured with a self-comparison method.
