High precision differential clock comparisons with a multiplexed optical lattice clock (2109.12237v1)

Abstract: Rapid progress in the precision and accuracy of optical atomic clocks over the last decade has advanced the frontiers of timekeeping, metrology, and quantum science. However, the stabilities of most optical clocks remain limited by the local oscillator rather than the atoms themselves, leaving room for further progress. Here we implement a "multiplexed" one-dimensional optical lattice clock, in which spatially-resolved, movable ensembles of ultra-cold strontium atoms are trapped in the same optical lattice, interrogated simultaneously by a shared clock laser, and read-out in parallel. By performing synchronized Ramsey interrogations of ensemble pairs we observe atom-atom coherence times up to 26 seconds, a 270-fold improvement over the atom-laser coherence time, demonstrate a relative stability of $9.7(4)\times10^{-18}/\sqrt{\tau}$ (where $\tau$ is the averaging time in seconds), and reach a fractional uncertainty of $8.9(3)\times 10^{-20}$ after 3.3 hours of averaging. These results demonstrate that applications requiring ultra-high-precision comparisons between optical atomic clocks need not be limited by the stability of the local oscillator. With multiple ensemble pairs, we realize a miniaturized clock network consisting of 6 atom ensembles, resulting in 15 unique pairwise clock comparisons with relative stabilities below $3\times10^{-17}/\sqrt{\tau}$. Finally, we demonstrate the capability to simultaneously load spatially-resolved, heterogeneous ensemble pairs of all four stable isotopes of strontium in a lattice. The unique capabilities offered by this platform pave the way for future studies of precision isotope shift measurements, spatially resolved characterization of limiting clock systematics, development of clock-based gravitational wave and dark matter detectors, and novel tests of relativity including measurements of the gravitational redshift at sub-centimeter scales.

High Precision Differential Clock Comparisons and the Progress of Optical Lattice Clocks

The paper "High precision differential clock comparisons with a multiplexed optical lattice clock" offers significant insights into advancing the precision and stability of optical atomic clocks, specifically through a novel approach using multiplexed optical lattice configurations. This document presents a robust methodology that addresses critical challenges in clock precision and stability, potentially influencing a wide range of practical and theoretical applications.

The authors detail the implementation of a "multiplexed" one-dimensional optical lattice clock, leveraging spatially-resolved ensembles of ultra-cold strontium atoms, which are trapped and interrogated simultaneously. The intrinsic innovation lies in performing synchronized Ramsey interrogations of atom pairs, allowing for atom-atom coherence times that extend to 26 seconds—a notable 270-fold increment when compared to the atom-laser coherence time. This results in a remarkable relative stability reaching $9.7(4)\times10^{-18}/\sqrt{\tau}$ and achieves a fractional uncertainty of $8.9(3)\times 10^{-20}$ after an average time of 3.3 hours.

The paper focuses on surpassing the limitations imposed by the local oscillator's stability in optical clocks, a common issue in precision timekeeping. By utilizing multiple ensemble pairs to form a miniaturized clock network, the research underscores the practicality of optical atomic clocks in high-precision applications, expanding clock comparisons beyond conventional constraints. With the inclusion of 15 unique pairwise comparisons from 6 ensemble sets, a relative stability below $3\times10^{-17}/\sqrt{\tau}$ is realized.

Further, their innovation extends to loading spatially-resolved, heterogeneous ensemble pairs of all four stable isotopes of strontium into the lattice. This approach offers routes for future investigations into precision isotope shift measurements, characterization of clock systematic limits, and furtherance of clock-based phenomena studies. These include gravitational wave and dark matter detection and conducting precise tests of relativity and gravitational redshift measurements at sub-centimeter scales.

From a theoretical standpoint, the research redefines quantum projection noise (QPN) limitations by demonstrating stability enhancements through the strategic use of multiplexing and simultaneous differential comparisons. While previous systems relied heavily on reducing the frequency noise of clock lasers, the innovative approach here capitalizes on minimizing environmental perturbations and optimizing interrogation times through ensemble methodology. The work convincingly shows the mitigation of noise through common-mode rejection and could pave the way for even more sophisticated clock developments, potentially integrating spin-squeezing techniques to transcend QPN limitations.

Practical implications of this research are far-reaching; miniaturized and highly stable optical clocks have clear advantages in applications necessitating time precision, such as relativistic geodesy and gravitational wave detection. These innovations offer promise particularly for mobile and space-bound clock systems where state-of-the-art, elaborate infrastructure may be impractical or restricted.

In summary, this work details a substantial refinement in optical atomic clock technology. While further evaluation of systematic differentials is ongoing, the authors have successfully demonstrated methods that could redefine precision thresholds in quantum timekeeping. The results, which leverage the intersection of quantum mechanics with applied physics, signal a shift towards practical, scalable solutions for some of the most challenging measurements in fundamental physics. Such advancements suggest that future research in this field may continue to break down traditional barriers, offering new insights and capabilities to both metrology and broader scientific inquiries.