Laser-induced fluorescence (LIF) performed on metastable ions is frequently used to probe the dynamics of ground-state ion motions in many laboratory plasmas. However, these measurements place restrictions on the metastable ion lifetime. Metastable states are produced from direct ionization of neutral atoms as well as ions in other electronic states, of which the former will only faithfully represent processes that act on the ion dynamics in a time shorter than the metastable lifetime. We present here the first experimental study of this type of systematic effect using wave-particle interaction in an argon multidipole plasma. The metastable lifetime and relative fraction of metastables produced from preexisting ions, necessary for correcting the LIF measurement errors, can be determined by fitting the experimental results with the theory we propose.

The charge degree of freedom in solid-state defects fundamentally underpins the electronic spin degree of freedom, a workhorse of quantum technologies. Here we measure, analyze, and control charge-state behavior in individual near-surface nitrogen-vacancy (NV) centers in diamond, where ${\mathrm{NV}}^{-}$ hosts the metrologically relevant electron spin. We find that ${\mathrm{NV}}^{-}$ initialization fidelity varies between individual centers and over time; we alleviate the deleterious effects of reduced ${\mathrm{NV}}^{-}$ initialization fidelity via logic-based initialization. Importantly, we also show that ${\mathrm{NV}}^{-}$ can ionize in the dark on experimentally relevant timescales, and we introduce measurement protocols that mitigate the compromising effects of charge conversion on spin measurements. We identify tunneling to a single local electron trap as the mechanism for ionization in the dark, and we develop novel NV-assisted techniques to control and read out the trap charge state. Our understanding and command of the NV’s local electrostatic environment will simultaneously guide materials design and provide unique functionalities with NV centers.

The cerium hexaboride (${\mathrm{CeB}}_6$) $f$-electron compound displays a rich array of low-temperature magnetic phenomena, including a “magnetically hidden” order, identified as multipolar in origin via advanced x-ray scattering. From first-principles electronic-structure results, we find that the antiferroquadrupolar (AFQ) ordering in ${\mathrm{CeB}}_6$ arises from crystal-field splitting and yields a band structure in agreement with experiments. With interactions of $p$ electrons between Ce and ${\mathrm{B}}_6$ being small, the electronic state of ${\mathrm{CeB}}_6$ is suitably described as $\mathrm{Ce}(4f^1{)}^{3+}(e^{-})({\mathrm{B}}_6{)}^{2-}$. The AFQ state of orbital spins is caused by an exchange interaction induced through spin-orbit interaction, which also splits the $\mathit{J}=5/2$ state into a ${\mathrm{\Gamma }}_8$ ground state and a ${\mathrm{\Gamma }}_7$ excited state. Within the smallest antiferromagnetic (AFM) (111) configuration, an orbital-ordered AFQ state appears during charge self-consistency, and it supports the appearance of a “hidden” order. Hydrostatic pressure (either applied or chemically induced) stabilizes the AFM (AFQ) states over a ferromagnetic one, as observed at low temperatures.

Despite intense efforts it has remained unresolved whether and how interfacial spin-orbit coupling (ISOC) affects spin transport across heavy-metal (HM)–ferromagnet (FM) interfaces. Here we report conclusive experiment evidence that the ISOC at HM/FM interfaces is the dominant mechanism for “spin memory loss”. An increase in ISOC significantly reduces, in a linear manner, the dampinglike spin-orbit torque (SOT) exerted on the FM layer via degradation of the spin transparency of the interface for spin currents generated in the HM. In addition, the fieldlike SOT is also dominated by the spin Hall contribution of the HM and decreases with increasing ISOC. This work reveals that ISOC at HM/FM interfaces should be minimized to advance efficient SOT devices through atomic layer passivation of the HM/FM interface or other means.

The spontaneous generation of charge-density-wave order in a Dirac fermion system via the natural mechanism of electron-phonon coupling is studied in the framework of the Holstein model on the honeycomb lattice. Using two independent and unbiased quantum Monte Carlo methods, the phase diagram as a function of temperature and coupling strength is determined. It features a quantum critical point as well as a line of thermal critical points. Finite-size scaling appears consistent with fermionic Gross-Neveu-Ising universality for the quantum phase transition and bosonic Ising universality for the thermal phase transition. The critical temperature has a maximum at intermediate couplings. Our findings motivate experimental efforts to identify or engineer Dirac systems with sufficiently strong and tunable electron-phonon coupling.

The effect of electron-electron interactions on Dirac fermions, and the possibility of an intervening spin-liquid phase between the semimetal and antiferromagnetic (AF) regimes, has been a focus of intense quantum simulation effort over the last five years. We use determinant quantum Monte Carlo simulations to study the Holstein model on a honeycomb lattice and explore the role of electron- phonon interactions on Dirac fermions. We show that they give rise to charge-density-wave (CDW) order and present evidence that this occurs only above a finite critical interaction strength. We evaluate the temperature for the transition into the CDW which, unlike the AF transition, can occur at finite values owing to the discrete nature of the broken symmetry.

We derive an action whose equations of motion contain the Poisson equation of Newtonian gravity. The construction requires a new notion of Newton-Cartan geometry based on an underlying symmetry algebra that differs from the usual Bargmann algebra. This geometry naturally arises in a covariant $1/c$ expansion of general relativity, with $c$ being the speed of light. By truncating this expansion at subleading order, we obtain the field content and transformation rules of the fields that appear in the action of Newtonian gravity. The equations of motion generalize Newtonian gravity by allowing for the effect of gravitational time dilation due to strong gravitational fields.

We report on new measurements of Cabibbo-suppressed semileptonic $D_s^{+}$ decays using $3.19{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ annihilation data sample collected at a center-of-mass energy of 4.178 GeV with the BESIII detector at the BEPCII collider. Our results include branching fractions $\mathcal{B}(D_s^{+}\to K^0{e}^{+}{\nu }_e)=[3.25\pm 0.38(\mathrm{stat})\pm 0.16(\mathrm{syst})]\times {10}^{-3}$ and $\mathcal{B}(D_s^{+}\to K^{*0}{e}^{+}{\nu }_e)=[2.37\pm 0.26(\mathrm{stat})\pm 0.20(\mathrm{syst})]\times {10}^{-3}$, which are much improved relative to previous measurements, and the first measurements of the hadronic form-factor parameters for these decays. For $D_s^{+}\to K^0{e}^{+}{\nu }_e$, we obtain $f_{+}(0)=0.720\pm 0.084(\mathrm{stat})\pm 0.013(\mathrm{syst})$, and for $D_s^{+}\to K^{*0}{e}^{+}{\nu }_e$, we find form-factor ratios $r_V=V(0)/A_1(0)=1.67\pm 0.34(\mathrm{stat})\pm 0.16(\mathrm{syst})$ and $r_2=A_2(0)/A_1(0)=0.77\pm 0.28(\mathrm{stat})\pm 0.07(\mathrm{syst})$.

Extracting parton distribution functions (PDFs) from lattice QCD calculation of quasi-PDFs has been actively pursued in recent years. We extend our proof of the multiplicative renormalizability of the quasiquark operators of Ishikawa et al. [Phys Rev. D 96, 094019 (2017)] to quasigluon operators, and demonstrated that quasigluon operators could be multiplicatively renormalized to all orders in perturbation theory, without mixing with other operators. We find that using a gauge-invariant UV regulator is essential for achieving this proof. With the multiplicative renormalizability of both quasiquark and quasigluon operators, and QCD collinear factorization of hadronic matrix elements of there operators into PDFs, extracting PDFs from lattice QCD calculated hadronic matrix elements of quasiparton operators could have a solid theoretical foundation.

We introduce an exactly integrable nonlinear model describing the dynamics of spinor solitons in space-dependent matrix gauge potentials of rather general types. The model is shown to be gauge equivalent to the integrable system of vector nonlinear Schrödinger equations known as the Manakov model. As an example we consider a self-attractive Bose-Einstein condensate with random spin-orbit coupling (SOC). If Zeeman splitting is also included, the system becomes nonintegrable. We illustrate this by considering the random walk of a soliton in a disordered SOC landscape. While at zero Zeeman splitting the soliton moves without scattering along linear trajectories in the random SOC landscape; at nonzero splitting it exhibits strong scattering by the SOC inhomogeneities. For a large Zeeman splitting, the integrability is restored. In this sense, the Zeeman splitting serves as a parameter controlling the crossover between two different integrable limits.

We report the experimental realization of a synthetic three-leg Hall tube with ultracold fermionic atoms in a one-dimensional optical lattice. The legs of the synthetic tube are composed of three hyperfine spin states of the atoms, and the cyclic interleg links are generated by two-photon Raman transitions between the spin states, resulting in a uniform gauge flux $\varphi$ penetrating each side plaquette of the tube. Using quench dynamics, we investigate the band structure of the Hall tube system for a commensurate flux $\varphi =2\pi /3$. Momentum-resolved analysis of the quench dynamics reveals a critical point of band gap closing as one of the interleg coupling strengths is varied, which is consistent with a topological phase transition predicted for the Hall tube system.

We present two quantum algorithms based on evolution randomization, a simple variant of adiabatic quantum computing, to prepare a quantum state $|x⟩$ that is proportional to the solution of the system of linear equations $A\overrightarrow{x}=\overrightarrow{b}$. The time complexities of our algorithms are $O\mathbf{(}{\kappa }^2\log (\kappa )/\epsilon \mathbf{)}$ and $O\mathbf{(}\kappa \log (\kappa )/\epsilon \mathbf{)}$, where $\kappa$ is the condition number of $A$ and $\epsilon$ is the precision. Both algorithms are constructed using families of Hamiltonians that are linear combinations of products of $A$, the projector onto the initial state $|b⟩$, and single-qubit Pauli operators. The algorithms are conceptually simple and easy to implement. They are not obtained from equivalences between the gate model and adiabatic quantum computing. They do not use phase estimation or variable-time amplitude amplification, and do not require large ancillary systems. We discuss a gate-based implementation via Hamiltonian simulation and prove that our second algorithm is almost optimal in terms of $\kappa$. Like previous methods, our techniques yield an exponential quantum speed-up under some assumptions. Our results emphasize the role of Hamiltonian-based models of quantum computing for the discovery of important algorithms.

Population annealing is a powerful tool for large-scale Monte Carlo simulations. We adapt this method to molecular dynamics simulations and demonstrate its excellent accelerating effect by simulating the folding of a short peptide commonly used to gauge the performance of algorithms. The method is compared to the well established parallel tempering approach and is found to yield similar performance for the same computational resources. In contrast to other methods, however, population annealing scales to a nearly arbitrary number of parallel processors, and it is thus a unique tool that enables molecular dynamics to tap into the massively parallel computing power available in supercomputers that is so much needed for a range of difficult computational problems.

The Hubble constant ($H_0$) estimated from the local Cepheid-supernova distance ladder is in $3\text{−}\sigma$ tension with the value extrapolated from cosmic microwave background (CMB) data assuming the standard cosmological model. Whether this tension represents new physics or systematic effects is the subject of intense debate. Here, we investigate how new, independent $H_0$ estimates can arbitrate this tension, assessing whether the measurements are consistent with being derived from the same model using the posterior predictive distribution (PPD). We show that, with existing data, the inverse distance ladder formed from BOSS baryon acoustic oscillation measurements and the Pantheon supernova sample yields an $H_0$ posterior near identical to the Planck CMB measurement. The observed local distance ladder value is a very unlikely draw from the resulting PPD. Turning to the future, we find that a sample of $\sim 50$ binary neutron star “standard sirens” (detectable within the next decade) will be able to adjudicate between the local and CMB estimates.

The region of heavy calcium isotopes forms the frontier of experimental and theoretical nuclear structure research where the basic concepts of nuclear physics are put to stringent test. The recent discovery of the extremely neutron-rich nuclei around ${}^{60}\mathrm{Ca}$ O. B. Tarasov et al. [Phys. Rev. Lett. 121, 022501 (2018)] and the experimental determination of masses for ${}^{55–57}\mathrm{Ca}$ S. Michimasa et al. [Phys. Rev. Lett. 121, 022506 (2018)] provide unique information about the binding energy surface in this region. To assess the impact of these experimental discoveries on the nuclear landscape’s extent, we use global mass models and statistical machine learning to make predictions, with quantified levels of certainty, for bound nuclides between Si and Ti. Using a Bayesian model averaging analysis based on Gaussian-process-based extrapolations we introduce the posterior probability $p_{\mathrm{ex}}$ for each nucleus to be bound to neutron emission. We find that extrapolations for drip-line locations, at which the nuclear binding ends, are consistent across the global mass models used, in spite of significant variations between their raw predictions. In particular, considering the current experimental information and current global mass models, we predict that ${}^{68}\mathrm{Ca}$ has an average posterior probability $p_{\mathrm{ex}}\approx 76\%$ to be bound to two-neutron emission while the nucleus ${}^{61}\mathrm{Ca}$ is likely to decay by emitting a neutron ($p_{\mathrm{ex}}\approx 46\%$).

We propose an experiment to find evidence of the formation of light-induced crossings provoked by cavity quantum radiation on simple molecules by using state-of-the-art optical cavities, molecular beams, pump-probe laser schemes, and velocity mapping detectors for fragmentation. The procedure is based on prompt excitation and subsequent dissociation in a three-state scheme of a polar diatomic molecule, with two ${}^1\mathrm{\Sigma }$ states (ground and first excited) coupled first by the UV pump laser and then by the cavity radiation, and a third fully dissociative state ${}^1\mathrm{\Pi }$ coupled through the delayed UV/V probe laser. The observed enhancement of photodissociation yields in the ${}^1\mathrm{\Pi }$ channel at given time delays between the pump and probe lasers unambiguously indicates the formation of a light-induced crossing between the two ${}^1\mathrm{\Sigma }$ field-dressed potential energy curves of the molecule. Also, the production of cavity photons out of the vacuum field state via nonadiabatic effects represents a showcase of a molecular dynamical Casimir effect. To simulate the experiment outcome, we perform ab initio coherent quantum dynamics of the molecule LiF subject to external lasers and quantum cavity interactions in the strong coupling regime, using a product grid representation of the total polaritonic wave function for both vibrational and photon degrees of freedom.

We bring the set of linear quantum operations, important for many fundamental studies in photonic systems, to the material domain of collective excitations known as spin waves. Using the ac Stark effect we realize quantum operations on single excitations and demonstrate a spin-wave analog of the Hong-Ou-Mandel effect, realized via a beam splitter implemented in the spin-wave domain. Our scheme equips atomic-ensemble-based quantum repeaters with quantum information processing capability and can be readily brought to other physical systems, such as doped crystals or room-temperature atomic ensembles.

Motivated by electronic transport in graphenelike structures, we study the diffusion of a classical point particle in Fermi potentials situated on a triangular lattice. We call this system a soft Lorentz gas, as the hard disks in the conventional periodic Lorentz gas are replaced by soft repulsive scatterers. A thorough computational analysis yields both normal and anomalous (super)diffusion with an extreme sensitivity on model parameters. This is due to an intricate interplay between trapped and ballistic periodic orbits, whose existence is characterized by tonguelike structures in parameter space. These results hold even for small softness, showing that diffusion in the paradigmatic hard Lorentz gas is not robust for realistic potentials, where we find an entirely different type of diffusion.