Measurement of the ²⁷Al⁺ and ⁸⁷Sr absolute optical frequencies

We perform absolute measurement of the ²⁷Al⁺ single-ion and ⁸⁷Sr neutral lattice clock frequencies at the National Institute of Standards and Technology and JILA at the University of Colorado against a global ensemble of primary frequency standards. Over an eight month period multiple measurements yielded the mean optical atomic transition frequencies ${\nu }_{\text{A}{\text{l}}^{+}}=\mathrm{1\; 121\; 015\; 393\; 207\; 859.50}\left(0.36\right)\text{Hz}$ and ${\nu }_{\text{Sr}}=\mathrm{429\; 228\; 004\; 229\; 873.19}\left(0.15\right)\text{Hz}$ , where the stated uncertainties are dominated by statistical noise and gaps in the observation interval ('dead-time' uncertainty).