We investigate the $2{}^3{S}_1–2{}^3{P}_J$ ($J=0$, 1, 2) transitions in ${}^6{\mathrm{Li}}^{+}$ using the optical Ramsey technique and achieve the most precise values of the hyperfine splittings of the $2{}^3{S}_1$ and $2{}^3{P}_J$ states, with smallest uncertainty of about 10 kHz. The present results reduce the uncertainties of previous experiments by a factor of 5 for the $2{}^3{S}_1$ state and a factor of 50 for the $2{}^3{P}_J$ states, and are in better agreement with theoretical values. Combining our measured hyperfine intervals of the $2{}^3{S}_1$ state with the latest quantum electrodynamic (QED) calculations, the improved Zemach radius of the ${}^6\mathrm{Li}$ nucleus is determined to be 2.44(2) fm, with the uncertainty entirely due to the uncalculated QED effects of order $m{\alpha }^7$. The result is in sharp disagreement with the value 3.71(16) fm determined from simple models of the nuclear charge and magnetization distribution. We call for a more definitive nuclear physics value of the ${}^6\mathrm{Li}$ Zemach radius.

When a drop merges with its homophase, a liquid cylinder appears in certain conditions, which is pinched off leading to partial coalescence. We investigate the process experimentally and numerically, and find that the Rayleigth-Plateau instability is able to pinch off the cylinder when its height-to-neck ratio exceeds one. Surfactants are found to attenuate the cylinder and produce multiple droplets at moderate concentrations. For both the pinch-off of the mother drop and the subsequent breakup of the liquid threads in partial coalescence, the neck thinning is initially in the inertial (I) regime and then shifts to the inertial-viscous (IV) regime. An intermediate regime is seen at larger surfactant concentrations, which accelerates the thinning and favours the generation of multiple droplets.

Magnetic ordering beyond the standard dipolar order has attracted significant attention in recent years, but it remains an open question how to effectively manipulate such nontrivial order parameters using external perturbations such as electric currents or fields. In particular, it is desirable to have a conceptual tool similar to nonequilibrium spin currents in spintronics to describe the creation and transport of multipole moments. In this context, we present a theory for Cartesian spin magnetic multipole moments of Bloch quasiparticles and their transport based on a general gauge-invariant formula obtained using the wave packet approach. As a concrete example, we point out that the low-energy Hamiltonian of phosphorene subject to a perpendicular electric field has a valley structure that hosts magnetic octupole moments. The magnetic octupole moments can be exhibited by an in-plane electric current and lead to accumulation of staggered spin densities at the corners of a rectangular sample. Our Letter paves the way for systematically seeking and utilizing quasiparticles with higher-order magnetic multipole moments in crystal materials towards the emergence of multipoletronics.

We introduce a quantum virial expansion for the optical response of a doped two-dimensional semiconductor. As we show, this constitutes a perturbatively exact theory in the high-temperature or low-doping regime, where the electrons’ thermal wavelength is smaller than their interparticle spacing. We obtain exact analytic expressions for the photoluminescence and we predict new features such as a nontrivial shape of the attractive branch peak related to universal resonant exciton-electron scattering and an associated energy shift from the trion energy. Our theory furthermore allows us to formally unify the two distinct theoretical pictures that have been applied to this system, where we reveal that the predictions of the conventional trion picture correspond to a high-temperature and weak-interaction limit of Fermi-polaron theory. Our results are in excellent agreement with recent experiments on doped monolayer ${\mathrm{MoSe}}_2$ and they provide the foundation for modeling a range of emerging optically active materials such as van der Waals heterostructures.

Quantum nonlocality can be demonstrated without inputs (i.e., each party using a fixed measurement setting) in a network with independent sources. Here we consider this effect on ring networks, and show that the underlying quantum strategy can be partially characterized, or self-tested, from observed correlations. Applying these results to the triangle network allows us to show that the nonlocal distribution of Renou et al. [Phys. Rev. Lett. 123, 140401 (2019)] requires that (i) all sources produce a minimal amount of entanglement, (ii) all local measurements are entangled, and (iii) each local outcome features a minimal entropy. Hence we show that the triangle network allows for genuine network quantum nonlocality and certifiable randomness.

We demonstrate quantum logic enhanced sensitivity for a macroscopic ensemble of solid-state, hybrid two-qubit sensors. We achieve over a factor of 30 improvement in the single-shot signal-to-noise ratio, translating to an ac magnetic field sensitivity enhancement exceeding an order of magnitude for time-averaged measurements. Using the electronic spins of nitrogen vacancy (NV) centers in diamond as sensors, we leverage the on-site nitrogen nuclear spins of the NV centers as memory qubits, in combination with homogeneous and stable bias and control fields, ensuring that all of the $\sim {10}^9$ two-qubit sensors are sufficiently identical to permit global control of the NV ensemble spin states. We find quantum logic sensitivity enhancement for multiple measurement protocols with varying optimal sensing intervals, including XY8 and DROID-60 dynamical decoupling, as well as correlation spectroscopy, using an applied ac magnetic field signal. The results are independent of the nature of the target signal and broadly applicable to measurements using NV centers and other solid-state spin ensembles. This work provides a benchmark for macroscopic ensembles of quantum sensors that employ quantum logic or quantum error correction algorithms for enhanced sensitivity.

We present the first direct search for exotic Higgs boson decays $H\to \mathcal{AA}$, $\mathcal{A}\to \gamma \gamma$ in events with two photonlike objects. The hypothetical particle $\mathcal{A}$ is a low-mass spin-0 particle decaying promptly to a merged diphoton reconstructed as a single photonlike object. We analyze the data collected by the CMS experiment at $\sqrt{s}=13\mathrm{TeV}$ corresponding to an integrated luminosity of $136{\mathrm{fb}}^{-1}$. No excess above the estimated background is found. We set upper limits on the branching fraction $\mathcal{B}(H\to \mathcal{A}\mathcal{A}\to 4\gamma )$ of $(0.9–3.3)\times {10}^{-3}$ at 95% confidence level for masses of $\mathcal{A}$ in the range 0.1–1.2 GeV.

Charge radii of neutron deficient ${}^{40}\mathrm{Sc}$ and ${}^{41}\mathrm{Sc}$ nuclei were determined using collinear laser spectroscopy. With the new data, the chain of Sc charge radii extends below the neutron magic number $N=20$ and shows a pronounced kink, generally taken as a signature of a shell closure, but one notably absent in the neighboring Ca, K, and Ar isotopic chains. Theoretical models that explain the trend at $N=20$ for the Ca isotopes cannot reproduce this puzzling behavior.

Skimmed supersonic beams provide intense, cold, collision-free samples of atoms and molecules and are one of the most widely used tools in atomic and molecular laser spectroscopy. High-resolution optical spectra are typically recorded in a perpendicular arrangement of laser and supersonic beams to minimize Doppler broadening. Typical Doppler widths are nevertheless limited to tens of MHz by the residual transverse-velocity distribution in the gas-expansion cones. We present an imaging method to overcome this limitation that exploits the correlation between the positions of the atoms and molecules in the supersonic expansion and their transverse velocities, and thus their Doppler shifts. With the example of spectra of $(1s)(np){}^3{P}_{0-2}\leftarrow (1s)(2s){}^3{S}_1$ transitions to high Rydberg states of metastable triplet He, we demonstrate the suppression of the residual Doppler broadening and a reduction of the full linewidths at half maximum to only about 1 MHz in the UV. Using a retroreflection arrangement for the laser beam and a cross-correlation method, we determine Doppler-free spectra without any signal loss from the selection, by imaging, of atoms within ultranarrow transverse-velocity classes. As an illustration, we determine the ionization energy of triplet metastable He and confirm the significant discrepancy between recent experimental [G. Clausen et al., Phys. Rev. Lett. 127, 093001 (2021)] and high-level theoretical [V. Patkós et al., Phys. Rev. A 103, 042809 (2021)] values of this quantity.

We demonstrate a novel scheme for Raman-pulse and Bragg-pulse atom interferometry based on the 5S-6P blue transitions of ${}^{87}\mathrm{Rb}$ that provides an increase by a factor $\sim 2$ of the interferometer phase due to accelerations with respect to the commonly used infrared transition at 780 nm. A narrow-linewidth laser system generating more than 1 W of light in the 420–422 nm range was developed for this purpose. Used as a cold-atom gravity gradiometer, our Raman interferometer attains a stability to differential acceleration measurements of $1\times {10}^{-8}g$ at 1 s and $2\times {10}^{-10}g$ after 2000 s of integration time. When operated on first-order Bragg transitions, the interferometer shows a stability of $6\times {10}^{-8}g$ at 1 s, averaging to $1\times {10}^{-9}g$ after 2000 s of integration time. The instrument sensitivity, currently limited by the noise due to spontaneous emission, can be further improved by increasing the laser power and the detuning from the atomic resonance. The present scheme is attractive for high-precision experiments as, in particular, for the determination of the Newtonian gravitational constant.

Cold atoms in an optical cavity have been widely used for quantum simulations of many-body physics, where the quantum control capability has been advancing rapidly in recent years. Here, we show the atom cavity system is universal for quantum optimization with arbitrary connectivity. We consider a single-mode cavity and develop a Raman coupling scheme by which the engineered quantum Hamiltonian for atoms directly encodes number partition problems. The programmability is introduced by placing the atoms at different positions in the cavity with optical tweezers. The number partition problem solution is encoded in the ground state of atomic qubits coupled through a photonic cavity mode, which can be reached by adiabatic quantum computing. We construct an explicit mapping for the 3-SAT and vertex cover problems to be efficiently encoded by the cavity system, which costs linear overhead in the number of atomic qubits. The atom cavity encoding is further extended to quadratic unconstrained binary optimization problems. The encoding protocol is optimal in the cost of atom number scaling with the number of binary degrees of freedom of the computation problem. Our theory implies the atom cavity system is a promising quantum optimization platform searching for practical quantum advantage.

The cosmological lithium problem—that theory predicts a primordial abundance far higher than the observed value—has resisted decades of attempts by cosmologists, nuclear physicists, and astronomers alike to root out systematics. We reconsider this problem in the setting of the standard model extended by gauged baryon minus lepton number, which we spontaneously break by a scalar with charge six. Cosmic strings from this breaking can support interactions converting three protons into three positrons, and we argue that an “electric”-“magnetic” interplay can give this process an amplified, strong-scale cross section in an analog of the Callan-Rubakov effect. We suggest such cosmic strings have disintegrated $\mathcal{O}(1)$ of the primordial lithium nuclei, and lay out what is necessary for this scheme to succeed. To our knowledge this is the first new physics mechanism with microphysical justification for the abundance of lithium uniquely to be modified after big bang nucleosynthesis.

We propose a construction of generalized cuts of Feynman integrals as an operation on the domain of the Feynman parametric integral. A set of on-shell conditions removes the corresponding boundary components of the integration domain, in favor of including a boundary component from the second Symanzik polynomial. Hence integration domains are full-dimensional spaces with finite volumes, rather than being localized around poles. As initial applications, we give new formulations of maximal cuts, and we provide a simple derivation of a certain linear relation among cuts from the inclusion-exclusion principle.

The first observation of the production of $W^{\pm }{W}^{\pm }$ bosons from double parton scattering processes using same-sign electron-muon and dimuon events in proton-proton collisions is reported. The data sample corresponds to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ recorded at a center-of-mass energy of 13 TeV using the CMS detector at the CERN LHC. Multivariate discriminants are used to distinguish the signal process from the main backgrounds. A binned maximum likelihood fit is performed to extract the signal cross section. The measured cross section for production of same-sign $W$ bosons decaying leptonically is $80.7\pm 11.2(\mathrm{stat}){}_{-8.6}^{+9.5}(\mathrm{syst})\pm 12.1(\mathrm{model})\mathrm{fb}$, whereas the measured fiducial cross section is $6.28\pm 0.81(\mathrm{stat})\pm 0.69(\mathrm{syst})\pm 0.37(\mathrm{model})\mathrm{fb}$. The observed significance of the signal is 6.2 standard deviations above the background-only hypothesis.

A search for the rare $\eta \to {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$ double-Dalitz decay is performed using a sample of proton-proton collisions, collected by the CMS experiment at the CERN LHC with high-rate muon triggers during 2017 and 2018 and corresponding to an integrated luminosity of $101{\mathrm{fb}}^{-1}$. A signal having a statistical significance well in excess of 5 standard deviations is observed. Using the $\eta \to {\mu }^{+}{\mu }^{-}$ decay as normalization, the branching fraction $\mathcal{B}(\eta \to {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-})=[5.0\pm 0.8(\mathrm{stat})\pm 0.7(\mathrm{syst})\pm 0.7({\mathcal{B}}_{2\mu })]\times {10}^{-9}$ is measured, where the last term is the uncertainty in the normalization channel branching fraction. This work achieves an improved precision of over 5 orders of magnitude compared to previous results, leading to the first measurement of this branching fraction, which is found to agree with theoretical predictions.