Physics

Atomic physics

Multiplexing

Metrology

Atomic clock

Superfluidity

Coherence (philosophical gambling strategy)

Computer science

Quantum mechanics

Telecommunications

Optical lattice

Nature

Rapid progress in optical atomic clock performance has advanced the frontiers of timekeeping, metrology and quantum science1–3. Despite considerable efforts, the instabilities of most optical clocks remain limited by the local oscillator rather than the atoms themselves4,5. Here we implement a ‘multiplexed’ one-dimensional optical lattice clock, in which spatially resolved strontium atom ensembles are trapped in the same optical lattice, interrogated simultaneously by a shared clock laser and read-out in parallel. In synchronous Ramsey interrogations of ensemble pairs we observe atom–atom coherence times of 26 s, a 270-fold improvement over the measured atom–laser coherence time, demonstrate a relative instability of                                                                   $$9.7(4)\times {10}^{-18}/\sqrt{\tau }$$                               (where τ is the averaging time) and reach a relative statistical uncertainty of 8.9 × 10−20 after 3.3 h of averaging. These results demonstrate that applications involving optical clock comparisons need not be limited by the instability of the local oscillator. We further realize a miniaturized clock network consisting of 6 atomic ensembles and 15 simultaneous pairwise comparisons with relative instabilities below                                                                   $$3\times {10}^{-17}/\sqrt{\tau }$$                              , and prepare spatially resolved, heterogeneous ensemble pairs of all four stable strontium isotopes. These results pave the way for multiplexed precision isotope shift measurements, spatially resolved characterization of limiting clock systematics, the development of clock-based gravitational wave and dark matter detectors6–12 and new tests of relativity in the lab13–16. Multiple ultracold ensembles of strontium atoms are trapped in the same optical lattice, realizing a multiplexed optical clock where precision measurements can benefit from having all atoms share the same trapping light and clock laser.

Differential clock comparisons with a multiplexed optical lattice clock