Submarine fiber optic earthquake detection: Seismic networks detect earthquakes and are common on continents, where they are easy to install. However, most of Earth's surface is under the oceans, where placing seismometers is difficult. Marra et al. now find that ordinary submarine telecommunication cables can be used to detect earthquakes. Small strain changes associated with the passage of seismic waves were detected with laser light sent through in-use fiber optic cables by ultrastable lasers. This strategy could turn intercontinental fiber optic cables into ocean-bottom strain sensors, dramatically improving our ability to record earthquakes. Science , this issue p. 486

We demonstrate a novel way of synthesizing spin-orbit interactions in ultracold quantum gases, based on a single-photon optical clock transition coupling two long-lived electronic states of two-electron ${}^{173}\mathrm{Yb}$ atoms. By mapping the electronic states onto effective sites along a synthetic “electronic” dimension, we have engineered fermionic ladders with synthetic magnetic flux in an experimental configuration that has allowed us to achieve uniform fluxes on a lattice with minimal requirements and unprecedented tunability. We have detected the spin-orbit coupling with fiber-link-enhanced clock spectroscopy and directly measured the emergence of chiral edge currents, probing them as a function of the flux. These results open new directions for the investigation of topological states of matter with ultracold atomic gases.

Over five years, we have compared the hyperfine frequencies of ${}^{133}\mathrm{C}\mathrm{s}$ and ${}^{87}\mathrm{R}\mathrm{b}$ atoms in their electronic ground state using several laser-cooled ${}^{133}\mathrm{C}\mathrm{s}$ and ${}^{87}\mathrm{R}\mathrm{b}$ atomic fountains with an accuracy of $\sim {10}^{-15}$. These measurements set a stringent upper bound to a possible fractional time variation of the ratio between the two frequencies: $\frac{d}{dt}\ln [({\nu }_{\mathrm{R}\mathrm{b}})/({\nu }_{\mathrm{C}\mathrm{s}})]=(0.2\pm 7.0)\times {10}^{-16}{\mathrm{y}\mathrm{r}}^{-1}$ ($1\sigma$ uncertainty). The same limit applies to a possible variation of the quantity $({\mu }_{\mathrm{R}\mathrm{b}}/{\mu }_{\mathrm{C}\mathrm{s}}){\alpha }^{-0.44}$, which involves the ratio of nuclear magnetic moments and the fine structure constant.

We report on the first direct observation of fast spin-exchange coherent oscillations between different long-lived electronic orbitals of ultracold ${}^{173}\mathrm{Yb}$ fermions. We measure, in a model-independent way, the strength of the exchange interaction driving this coherent process. This observation allows us to retrieve important information on the interorbital collisional properties of ${}^{173}\mathrm{Yb}$ atoms and paves the way to novel quantum simulations of paradigmatic models of two-orbital quantum magnetism.

Optical fiber–based sensing technology can drastically improve Earth observations by enabling the use of existing submarine communication cables as seafloor sensors. Previous interferometric and polarization-based techniques demonstrated environmental sensing over cable lengths up to 10,500 kilometers. However, measurements were limited to the integrated changes over the entire length of the cable. We demonstrate the detection of earthquakes and ocean signals on individual spans between repeaters of a 5860-kilometer-long transatlantic cable rather than the whole cable. By applying this technique to the existing undersea communication cables, which have a repeater-to-repeater span length of 45 to 90 kilometers, the largely unmonitored ocean floor could be instrumented with thousands of permanent real-time environmental sensors without changes to the underwater infrastructure.