Two lutetium-176 ion clocks at NUS agree near 1 × 10−19
Arnold and colleagues compare two 176Lu+ ion clocks at the National University of Singapore. Each has a fractional frequency uncertainty near 1 × 10−19. The measured relative frequency difference is −0.1 ± 5.7 statistical ± 1.0 systematic, times 10−19. The university describes the clocks as the most accurate it has reported, using light near 848 nanometres at room temperature.
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Two clocks, one uncertainty near 1 × 10−19
Arnold and colleagues at the Centre for Quantum Technologies, National University of Singapore, compare two 176Lu+ ion clocks. Each has a fractional frequency uncertainty near 1 × 10−19. The university's own account, published on 23 September, calls these lutetium ion clocks the most accurate the laboratory has described. The comparison in that account uses light near 848 nanometres and runs at room temperature. The paper's uncertainty, near 1 × 10−19, is the figure. The university's sentence is the laboratory's description of the same pair of clocks, not a second experiment with a different ion. Two independent systems of the same species are what the paper says it compared.[1], [2]
The measured difference
The measured relative frequency difference is −0.1 ± 5.7 statistical ± 1.0 systematic, times 10−19. The evaluated uncertainties sit below 10−18. The paper writes that same-species verification remains open work in the debate over an optical standard for the second. The difference and the uncertainty are the result a reader can check: two clocks, a gap of −0.1 ± 5.7 statistical ± 1.0 systematic, times 10−19, and an uncertainty near 1 × 10−19 for each. The university adds a scale for that precision. A frequency difference at this level could resolve a height of about 5 millimetres. That height is the university's translation of the precision, not a length the clocks measured in a workshop.[1], [2]
A height of about 5 millimetres
The National University of Singapore says a frequency difference at this precision could resolve a height of about 5 millimetres. The light is near 848 nanometres, and the comparison runs at room temperature. Barrett's description, in the university account, calls the clocks the most accurate the laboratory has reported. The paper's open point remains: same-species verification is still open work if the second is to rest on an optical standard. The 176Lu+ pair, the uncertainty near 1 × 10−19, and the difference of −0.1 ± 5.7 statistical ± 1.0 systematic, times 10−19, are the measurement. The 5 millimetres and the 848 nanometres are the university's way of saying what that measurement can separate, and at what wavelength the clocks were compared.[1], [2]
