Recent progress on the 27Al+ ion optical clock

An aluminium ion optical clock is under development at Huazhong University of Science and Technology. The 25Mg+ ion is chosen as logic ion to sympathetically cool an Al+ ion and to detect its states. The 25Mg+ ion is cooled to the motional ground state through Raman sideband cooling as the first step for quantum logic spectroscopy. Ultra-stable lasers for the interrogation of the clock transition are developed. The instability of the laser beat frequency is 1.2 x 10-15 at 1 s, which is close to the thermal noise limit of the reference cavity.