A proposal for detecting dark matter originating from light fields rather than particles makes use of existing networks of atomic clocks to measure time discrepancies between clocks that are spatially separated. The cosmological applications of atomic clocks1,2,3 so far have been limited to searches for the uniform-in-time drift of fundamental constants4. We point out that a transient-in-time change of fundamental constants can be induced by dark-matter objects that have large spatial extent, such as stable topological defects5 built from light non-Standard Model fields. Networks of correlated atomic clocks, some of them already in existence6, such as the Global Positioning System, can be used as a powerful tool to search for topological defect dark matter, thus providing another important fundamental physics application for the ever-improving accuracy of atomic clocks. During the encounter with an extended dark-matter object, as it sweeps through the network, initially synchronized clocks will become desynchronized. Time discrepancies between spatially separated clocks are expected to exhibit a distinct signature, encoding the defect’s space structure and its interaction strength with atoms.

Recently invented and demonstrated optical lattice clocks hold great promise for improving the precision of modern time keeping. These clocks aim at the 10-18 fractional accuracy, which translates into a clock that would neither lose nor gain a fraction of a second over an estimated age of the Universe. In these clocks, millions of atoms are trapped and interrogated simultaneously, dramatically improving clock stability. Here the principles of operation of these clocks are discussed and, in particular, a novel concept of magic trapping of atoms in optical lattices. Recently proposed microwave lattice clocks are also highlights and several applications that employ the optical lattice clocks as a platform for precision measurements and quantum information processing.

We carry out high-precision calculation of parity violation in a cesium atom, reducing theoretical uncertainty by a factor of 2 compared to previous evaluations. We combine previous measurements with calculations and extract the weak charge of the ${}^{133}\mathrm{Cs}$ nucleus, $Q_W=-73.16(29{)}_{\mathrm{expt}}(20{)}_{\mathrm{theor}}$. The result is in agreement with the standard model (SM) of elementary particles. This is the most accurate to-date test of the low-energy electroweak sector of the SM. In combination with the results of high-energy collider experiments, we confirm the energy dependence (or “running”) of the electroweak force over an energy range spanning 4 orders of magnitude (from $\sim 10\mathrm{MeV}$ to $\sim 100\mathrm{GeV}$). Additionally, our result places constraints on a variety of new physics scenarios beyond the SM. In particular, we increase the lower limit on the masses of extra $Z$ bosons predicted by models of grand unification and string theories.

Numerous theories extending beyond the standard model of particle physics predict the existence of bosons that could constitute dark matter. In the standard halo model of galactic dark matter, the velocity distribution of the bosonic dark matter field defines a characteristic coherence timeτ_c. Until recently, laboratory experiments searching for bosonic dark matter fields have been in the regime where the measurement timeTsignificantly exceedsτ_c, so null results have been interpreted by assuming a bosonic field amplitude Φ₀fixed by the average local dark matter density. Here we show that experiments operating in theT ≪ τ_cregime do not sample the full distribution of bosonic dark matter field amplitudes and therefore it is incorrect to assume a fixed value of Φ₀when inferring constraints. Instead, in order to interpret laboratory measurements (even in the event of a discovery), it is necessary to account for the stochastic nature of such a virialized ultralight field. The constraints inferred from several previous null experiments searching for ultralight bosonic dark matter were overestimated by factors ranging from 3 to 10 depending on experimental details, model assumptions, and choice of inference framework.

Cosmological observations indicate that dark matter makes up 85% of all matter in the universe yet its microscopic composition remains a mystery. Dark matter could arise from ultralight quantum fields that form macroscopic objects. Here we use the global positioning system as a ~ 50,000 km aperture dark matter detector to search for such objects in the form of domain walls. Global positioning system navigation relies on precision timing signals furnished by atomic clocks. As the Earth moves through the galactic dark matter halo, interactions with domain walls could cause a sequence of atomic clock perturbations that propagate through the satellite constellation at galactic velocities ~ 300 km s⁻¹. Mining 16 years of archival data, we find no evidence for domain walls at our current sensitivity level. This improves the limits on certain quadratic scalar couplings of domain wall dark matter to standard model particles by several orders of magnitude.

${\mathrm{LiSrAlF}}_6$ crystals doped with ${}^{229}\mathrm{Th}$ are used in a laser-based search for the nuclear isomeric transition. Two spectroscopic features near the nuclear transition energy are observed. The first is a broad excitation feature that produces redshifted fluorescence that decays with a timescale of a few seconds. The second is a narrow, laser-linewidth-limited spectral feature at $148.38219(4{)}_{\mathrm{stat}}(20{)}_{\mathrm{sys}}\mathrm{nm}$ [$2020407.3(5{)}_{\mathrm{stat}}(30{)}_{\mathrm{sys}}\mathrm{GHz}$] that decays with a lifetime of $568(13{)}_{\mathrm{stat}}(20{)}_{\mathrm{sys}}\mathrm{s}$. This feature is assigned to the excitation of the ${}^{229}\mathrm{Th}$ nuclear isomeric state, whose energy is found to be $8.355733(2{)}_{\mathrm{stat}}(10{)}_{\mathrm{sys}}\mathrm{eV}$ in ${}^{229}\mathrm{Th}:{\mathrm{LiSrAlF}}_6$.