A high-accuracy optical clock via three-level coherence in neutral   bosonic $^{88}$Sr
  An optical atomic clock scheme is developed that utilizes two lasers to establish coherent coupling between the $5s^2 \phantom{}^1S_0$ ground state of $^{88}$Sr and the first excited state, $5s5p \phantom{}^3P_0$. The coupling is mediated by the broad $5s5p \phantom{}^1P_1$ state, exploiting the phenomenon of electromagnetically induced transparency. The effective linewidth of the clock transition can be chosen at will by adjusting the laser intensity. By trapping the $^{88}$Sr atoms in an optical lattice, long interaction times with the two lasers are ensured; Doppler and recoil effects are eliminated. Based on a careful analysis of systematic errors, a clock accuracy of better than $2\times 10^{-17}$ is expected. 
Robin Santra, Ennio Arimondo, Tetsuya Ido, Chris H. Greene, and Jun Ye