What it is
The authors built two optical frequency references, each based on a single trapped lutetium-176 ion and each with an evaluated fractional frequency uncertainty near 1 × 10⁻¹⁹, and compared them directly using correlation spectroscopy. The two agreed: their measured relative frequency difference was −0.1 × 10⁻¹⁹, with a statistical uncertainty of 5.7 × 10⁻¹⁹ and a systematic uncertainty of 1.0 × 10⁻¹⁹. Both are practical systems that operate at room temperature.
Why it matters
Optical atomic clocks have far surpassed their microwave predecessors, and a redefinition of the SI second is anticipated, but while the community seeks consensus on a new standard, verifying accuracy by comparing two independent clocks of the same species at comparable levels had remained an outstanding challenge. Two independent lutetium-ion systems agreeing at the 5.7 × 10⁻¹⁹ level supplies exactly that kind of check.
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Filed underAdvanced Frequency and Time Standards, GNSS positioning and interference, Atomic and Subatomic Physics Research