We present a measurement of the absolute frequency of the 5s$^2$ $^1$S$_0$ to 5s5p $^3$P$_0$ transition in $^{87}$Sr, which is a secondary representation of the SI second. We describe the optical lattice clock apparatus used for the measurement, and we focus in detail on how its systematic frequency shifts are evaluated with a total fractional uncertainty of $1 \times 10^{-17}$. Traceability to the International System of Units is provided via comparison to International Atomic Time (TAI). Gathering data over 5- and 15-day periods, with the lattice clock operating on average 74$\%$ of the time, we measure the frequency of the transition to be 429228004229873.1(5) Hz, which corresponds to a fractional uncertainty of $1 \times 10^{-15}$. We describe in detail how this uncertainty arises from the intermediate steps linking the optical frequency standard, through our local time scale UTC(NPL), to an ensemble of primary and secondary frequency standards which steer TAI. The calculated absolute frequency of the transition is in good agreement with recent measurements carried out in other laboratories around the world.

中文翻译：

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具有 1x10-17 不确定度的锶光学晶格时钟及其绝对频率的测量

我们提供了 $^{87}$Sr 中 5s$^2$ $^1$S$_0$ 到 5s5p $^3$P$_0$ 转换的绝对频率的测量值，这是SI 第二。我们描述了用于测量的光学晶格时钟装置，并详细介绍了如何以 $1 \times 10^{-17}$ 的总分数不确定性评估其系统频移。国际单位制的可追溯性是通过与国际原子时 (TAI) 的比较来提供的。收集 5 天和 15 天期间的数据，晶格时钟平均运行 74$\%$ 的时间，我们测量转换频率为 429228004229873.1(5) Hz，这对应于 1 美元的小数不确定性\times 10^{-15}$。我们详细描述了这种不确定性是如何从将光学频率标准通过我们的本地时间尺度 UTC(NPL) 链接到引导 TAI 的主要和次要频率标准集合的中间步骤产生的。计算出的跃迁绝对频率与世界各地其他实验室最近进行的测量非常吻合。