Frequency evaluation of the doubly forbidden $^1S_0\to ^3P_0$ transition   in bosonic $^{174}$Yb
  We report an uncertainty evaluation of an optical lattice clock based on the $^1S_0\leftrightarrow^3P_0$ transition in the bosonic isotope $^{174}$Yb by use of magnetically induced spectroscopy. The absolute frequency of the $^1S_0\leftrightarrow^3P_0$ transition has been determined through comparisons with optical and microwave standards at NIST. The weighted mean of the evaluations is $\nu$($^{174}$Yb)=518 294 025 309 217.8(0.9) Hz. The uncertainty due to systematic effects has been reduced to less than 0.8 Hz, which represents $1.5\times10^{-15}$ in fractional frequency. 
N. Poli, Z. W. Barber, N. D. Lemke, C. W. Oates, L. S. Ma, J. E.   Stalnaker, T. M. Fortier, S. A. Diddams, L. Hollberg, J. ...