We report high-fidelity state readout of a trapped ion qubit using a trap-integrated photon detector. We determine the hyperfine qubit state of a single ${}^9{\mathrm{Be}}^{+}$ ion held in a surface-electrode rf ion trap by counting state-dependent ion fluorescence photons with a superconducting nanowire single-photon detector fabricated into the trap structure. The average readout fidelity is 0.9991(1), with a mean readout duration of $46\mu \mathrm{s}$, and is limited by the polarization impurity of the readout laser beam and by off-resonant optical pumping. Because there are no intervening optical elements between the ion and the detector, we can use the ion fluorescence as a self-calibrated photon source to determine the detector quantum efficiency and its dependence on photon incidence angle and polarization.

Quantum criticality, as a fascinating quantum phenomenon, may provide significant advantages for quantum sensing. Here we propose a dynamic framework for quantum sensing with a family of Hamiltonians that undergo quantum phase transitions (QPTs). By giving the formalism of the quantum Fisher information (QFI) for quantum sensing based on critical quantum dynamics, we demonstrate its divergent feature when approaching the critical point. We illustrate the basic principle and the details of experimental implementation using quantum Rabi model. The framework is applicable to a variety of examples and does not rely on the stringent requirement for particular state preparation or adiabatic evolution. It is expected to provide a route towards the implementation of criticality-enhanced quantum sensing.

In the inflation-based cosmology the dark matter (DM) density component starts moving with respect to the universal expansion at $z_{\mathrm{eq}}\sim 3200$ while baryons remain frozen until $z_{\mathrm{rec}}\sim 1100$. It has been suggested that in this case postlinear corrections to the evolution of small fluctuations would result, for the standard $\mathrm{\Lambda }$-dominated cold DM (CDM) model, in delayed formation of early objects as supersonic advection flows develop after recombination, so baryons are not immediately captured by the DM gravity on small scales. We develop the hydrodynamical description of such two-component advection and show that, in the supersonic regime, the advection within irrotational fluids is governed by the gradient of the difference of the kinetic energies of the two (DM and baryonic here) components. We then apply this formalism to the case where DM is made up of LIGO-type black holes (BHs) and show that there the advection process on scales relevant for early structure collapse will differ significantly from the earlier discussed (CDM) case because of the additional granulation component to the density field produced during inflation. The advection here will lead efficiently to the common motion of the DM and baryon components on scales relevant for collapse and formation of first luminous sources. This leads to early collapse, making it easier to explain the existence of supermassive BHs observed in quasars at high $z>7$. The resultant net advection rate reaches minimum around $\lesssim {10}^9{M}_{\odot }$ and subsequently rises to a secondary maximum near the typical mass of $\sim {10}^{12}{M}_{\odot }$, which may be an important consideration for formation of galaxies at $z\lesssim (a\mathrm{few})$.

We compare two optical clocks based on the ${{}^{2}S}_{1/2}(F=0)\to {{}^{2}D}_{3/2}(F=2)$ electric quadrupole (E2) and the ${{}^{2}S}_{1/2}(F=0)\to {{}^{2}F}_{7/2}(F=3)$ electric octupole (E3) transition of ${{}^{171}\mathrm{Yb}}^{+}$ and measure the frequency ratio ${\nu }_{\mathrm{E}3}/{\nu }_{\mathrm{E}2}=0.932829404530965376(32)$, improving upon previous measurements by an order of magnitude. Using two caesium fountain clocks, we find ${\nu }_{E3}=642121496772645.10(8)\mathrm{Hz}$, the most accurate determination of an optical transition frequency to date. Repeated measurements of both quantities over several years are analyzed for potential violations of local position invariance. We improve by factors of about 20 and 2 the limits for fractional temporal variations of the fine structure constant $\alpha$ to $1.0(1.1)\times {10}^{-18}/\mathrm{yr}$ and of the proton-to-electron mass ratio $\mu$ to $-8(36)\times {10}^{-18}/\mathrm{yr}$. Using the annual variation of the Sun’s gravitational potential at Earth $\mathrm{\Phi }$, we improve limits for a potential coupling of both constants to gravity, $(c^2/\alpha )(d\alpha /d\mathrm{\Phi })=14(11)\times {10}^{-9}$ and $(c^2/\mu )(d\mu /d\mathrm{\Phi })=7(45)\times {10}^{-8}$.

Cosmological neutrinos have their greatest influence in voids: These are the regions with the highest neutrino to dark matter density ratios. The marked power spectrum can be used to emphasize low-density regions over high-density regions and, therefore, is potentially much more sensitive than the power spectrum to the effects of neutrino masses. Using 22 000 $N$-body simulations from the Quijote suite, we quantify the information content in the marked power spectrum of the matter field and show that it outperforms the standard power spectrum by setting constraints improved by a factor larger than 2 on all cosmological parameters. The combination of marked and standard power spectra allows us to place a $4.3\sigma$ constraint on the minimum sum of the neutrino masses with a volume equal to $1(\mathrm{Gpc}{h}^{-1}{)}^3$ and without cosmic microwave background priors. Combinations of different marked power spectra yield a $6\sigma$ constraint within the same conditions.

Exploring the nature of exotic multiquark candidates such as the X(3872) plays a pivotal role in understanding quantum chromodynamics (QCD). Despite significant efforts, consensus on their internal structures is still lacking. As a prime example, it remains a pressing open question to decipher the X(3872) state between two popular exotic configurations: a loose hadronic molecule or a compact tetraquark. We demonstrate a novel approach to help address this problem by studying the X(3872) production in heavy ion collisions, where a hot fireball with ample light as well as charm (anti-)quarks is available for producing the exotics. Adopting a multiphase transport model (AMPT) for describing such collisions and implementing appropriate production mechanism of either molecule or tetraquark picture, we compute and compare a series of observables for X(3872) in Pb-Pb collisions at the Large Hadron Collider. We find the fireball volume plays a crucial role, leading to a 2-order-of-magnitude difference in the X(3872) yield and a markedly different centrality dependence between hadronic molecules and compact tetraquarks, thus offering a unique opportunity for distinguishing the two scenarios. We also make the first prediction of X(3872) elliptic flow coefficient to be tested by future experimental measurements.

We investigate the possible formation of a Bose-Einstein condensed phase of pions in the early Universe at nonvanishing values of lepton flavor asymmetries. A hadron resonance gas model with pion interactions, based on first-principle lattice QCD simulations at nonzero isospin density, is used to evaluate cosmic trajectories at various values of electron, muon, and tau lepton asymmetries that satisfy the available constraints on the total lepton asymmetry. The cosmic trajectory can pass through the pion condensed phase if the combined electron and muon asymmetry is sufficiently large: $|l_e+l_{\mu }|\gtrsim 0.1$, with little sensitivity to the difference $l_e-l_{\mu }$ between the individual flavor asymmetries. Future constraints on the values of the individual lepton flavor asymmetries will thus be able to either confirm or rule out the condensation of pions during the cosmic QCD epoch. We demonstrate that the pion condensed phase leaves an imprint both on the spectrum of primordial gravitational waves and on the mass distribution of primordial black holes at the QCD scale, e.g., the black hole binary of recent LIGO event GW190521 can be formed in that phase.

We present the formation of homonuclear ${\mathrm{Cs}}_2$, ${\mathrm{K}}_2$, and heteronuclear CsK long-range Rydberg molecules in a dual-species magneto-optical trap for ${}^{39}\mathrm{K}$ and ${}^{133}\mathrm{Cs}$ by one-photon UV photoassociation. The different ground-state-density dependence of homo- and heteronuclear photoassociation rates and the detection of stable molecular ions resulting from autoionization provide an unambiguous assignment. We perform bound-bound millimeter-wave spectroscopy of long-range Rydberg molecules to access molecular states not accessible by one-photon photoassociation. Calculations based on the most recent theoretical model and atomic parameters do not reproduce the full set of data from homo- and heteronuclear long-range Rydberg molecules consistently. This shows that photoassociation and millimeter-wave spectroscopy of heteronuclear long-range Rydberg molecules provide a benchmark for the development of theoretical models.

Energy-efficient plasma-wakefield acceleration of particle bunches with low energy spread is a promising path to realizing compact free-electron lasers and particle colliders. High efficiency and low energy spread can be achieved simultaneously by strong beam loading of plasma wakefields when accelerating bunches with carefully tailored current profiles [M. Tzoufras et al., Phys. Rev. Lett. 101, 145002 (2008)]. We experimentally demonstrate such optimal beam loading in a nonlinear electron-driven plasma accelerator. Bunches with an initial energy of 1 GeV were accelerated by 45 MeV with an energy-transfer efficiency of $(42\pm 4)\%$ at a gradient of $1.3\mathrm{GV}/\mathrm{m}$ while preserving per-mille energy spreads with full charge coupling, demonstrating wakefield flattening at the few-percent level.

Plastic deformation in amorphous solids is known to be carried by stress-induced localized rearrangements of a few tens of particles, accompanied by the conversion of elastic energy to heat. Despite their central role in determining how glasses yield and break, the search for a simple and generally applicable definition of the precursors of those plastic rearrangements—the so-called shear transformation zones (STZs)—is still ongoing. Here we present a simple definition of STZs—based solely on the harmonic approximation of a glass’s energy. We explain why and demonstrate directly that our proposed definition of plasticity carriers in amorphous solids is more broadly applicable compared to anharmonic definitions put forward previously. Finally, we offer an open-source library that analyzes low-lying STZs in computer glasses and in laboratory materials such as dense colloidal suspensions for which the harmonic approximation is accessible. Our results constitute a physically motivated methodological advancement towards characterizing mechanical disorder in glasses, and understanding how they yield.

Electric field driven phase transformations require two phases with a mismatch in their electric polarization, as seen in antiferroelectric-to-ferroelectric transformations, where the ferroelectric phase has a permanent polarization that is favored under field. Many other nonferroelectric dielectric materials can become electrically polarized according to their electrical susceptibility, yet such induced polarizations are not generally considered capable of enabling a phase transformation. Here we explore a susceptibility-mismatch phase transformation in a paraelectric ceramic, yttria-doped zirconia. Using in situ x-ray diffraction at $550°\mathrm{C}$ we show that the monoclinic-to-tetragonal transformation can be driven directly by an electric field, providing experimental evidence of a paraelectric-to-paraelectric phase transformation. Considering the $\sim 1\%$ mechanical strain of this transformation, the resulting electromechanical coupling may have potential for solid-state electrical actuators.

Mixtures of ammonia and water are major components of the “hot ice” mantle regions of icy planets. The ammonia-rich ammonia hemihydrate (AHH) plays a pivotal role as it precipitates from water-rich mixtures under pressure. It has been predicted to form ionic high-pressure structures, with fully disintegrated water molecules. Utilizing Raman spectroscopy measurements up to 123 GPa and first-principles calculations, we report the spontaneous ionization of AHH under compression. Spectroscopic measurements reveal that molecular AHH begins to transform into an ionic state at 26 GPa and then above $\sim 69\mathrm{GPa}$ transforms into the fully ionic $P\overline{3}m1$ phase, AHH-III, characterized as ammonium oxide $({\mathrm{NH}}_4^{+}{)}_2{\mathrm{O}}^{2-}$.

We present results from the SPring-8 Angstrom Compact free electron LAser facility, where we used a high intensity ($\sim {10}^{20}\mathrm{W}/{\mathrm{cm}}^2$) x-ray pump x-ray probe scheme to observe changes in the ionic structure of silicon induced by x-ray heating of the electrons. By avoiding Laue spots in the scattering signal from a single crystalline sample, we observe a rapid rise in diffuse scattering and a transition to a disordered, liquidlike state with a structure significantly different from liquid silicon. The disordering occurs within 100 fs of irradiation, a timescale that agrees well with first principles simulations, and is faster than that predicted by purely inertial behavior, suggesting that both the phase change and disordered state reached are dominated by Coulomb forces. This method is capable of observing liquid scattering without masking signal from the ambient solid, allowing the liquid structure to be measured throughout and beyond the phase change.

We construct new many-body invariants for 2D Chern and 3D chiral hinge insulators characterizing quantized pumping of bulk dipole and quadrupole moments. The many-body invariants are written entirely in terms of many-body ground state wave functions on a torus geometry with twisted boundary conditions and a set of unitary operators. We present a number of supporting arguments for the invariants via topological field theory interpretation, adiabatic pumping argument, and direct mapping to free-fermion band indices. Therefore, the invariants explicitly encircle several different pillars of theoretical descriptions of topological phases. Furthermore, our many-body invariants are written in forms which can be directly employed in various numerics including the exact diagonalization and the density-matrix renormalization group simulations. We finally confirm our invariants by numerical computations including an infinite density-matrix renormalization group on quasi-one-dimensional systems.

We report a comprehensive de Haas–van Alphen (dHvA) study of the heavy-fermion material ${\mathrm{CeRhIn}}_5$ in magnetic fields up to 70 T. Several dHvA frequencies gradually emerge at high fields as a result of magnetic breakdown. Among them is the thermodynamically important ${\beta }_1$ branch, which has not been observed so far. Comparison of our angle-dependent dHvA spectra with those of the non-$4f$ compound ${\mathrm{LaRhIn}}_5$ and with band-structure calculations evidences that the Ce $4f$ electrons in ${\mathrm{CeRhIn}}_5$ remain localized over the whole field range. This rules out any significant Fermi-surface reconstruction, either at the suggested nematic phase transition at $B^{*}\approx 30\mathrm{T}$ or at the putative quantum critical point at $B_c\simeq 50\mathrm{T}$. Our results rather demonstrate the robustness of the Fermi surface and the localized nature of the $4f$ electrons inside and outside of the antiferromagnetic phase.

Graphene bilayers exhibit zero-energy flatbands at a discrete series of magic twist angles. In the absence of intrasublattice interlayer hopping, zero-energy states satisfy a Dirac equation with a non-Abelian SU(2) gauge potential that cannot be diagonalized globally. We develop a semiclassical WKB approximation scheme for this Dirac equation by introducing a dimensionless Planck’s constant proportional to the twist angle, solving the linearized Dirac equation around $AB$ and $BA$ turning points, and connecting Airy function solutions via bulk WKB wave functions. We find zero-energy solutions at a discrete set of values of the dimensionless Planck’s constant, which we obtain analytically. Our analytic flatband twist angles correspond closely to those determined numerically in previous work.

The intrinsic Hall effect allows for the generation of a nondissipative charge neutral current, such as a pure spin current generated via the spin Hall effect. Breaking of the spatial inversion or time reversal symmetries, or the spin-orbit interaction is generally considered necessary for the generation of such a charge neutral current. Here, we challenge this general concept and present generation and detection of a charge neutral current in a centrosymmetric material with little spin-orbit interaction. We employ bilayer graphene, and find enhanced nonlocal transport in the quantum Hall antiferromagnetic state, where spontaneous symmetry breaking occurs due to the electronic correlation.

We apply neutron spectroscopy to measure the magnetic dynamics in the $S=3/2$ magnet $\beta \text{−}{\mathrm{CaCr}}_2{\mathrm{O}}_4$ (${\mathrm{T}}_N=21\mathrm{K}$). The low-energy fluctuations, in the ordered state, resemble large-$S$ linear spin waves from the incommensurate ground state. However, at higher energy transfers, these semiclassical and harmonic dynamics are replaced by an energy and momentum broadened continuum of excitations. Applying kinematic constraints required for energy and momentum conservation, sum rules of neutron scattering, and comparison against exact diagonalization calculations, we show that the dynamics at high-energy transfers resemble low-$S$ one-dimensional quantum fluctuations. $\beta \text{−}{\mathrm{CaCr}}_2{\mathrm{O}}_4$ represents an example of a magnet at the border between classical Néel and quantum phases, displaying dual characteristics.

In the cubic chiral magnet ${\mathrm{Cu}}_2{\mathrm{OSeO}}_3$ a low-temperature skyrmion state (LTS) and a concomitant tilted conical state are observed for magnetic fields parallel to $⟨100⟩$. Here, we report on the dynamic resonances of these novel magnetic states. After promoting the nucleation of the LTS by means of field cycling, we apply broadband microwave spectroscopy in two experimental geometries that provide either predominantly in-plane or out-of-plane excitation. By comparing the results to linear spin-wave theory, we clearly identify resonant modes associated with the tilted conical state, the gyrational and breathing modes associated with the LTS, as well as the hybridization of the breathing mode with a dark octupole gyration mode mediated by the magnetocrystalline anisotropies. Most intriguingly, our findings suggest that under decreasing fields the hexagonal skyrmion lattice becomes unstable with respect to an oblique deformation, reflected in the formation of elongated skyrmions.

Because of their long coherence times and potential for scalability, semiconductor quantum-dot spin qubits hold great promise for quantum information processing. However, maintaining high connectivity between quantum-dot spin qubits, which favor linear arrays with nearest neighbor coupling, presents a challenge for large-scale quantum computing. In this work, we present evidence for long-distance spin-chain-mediated superexchange coupling between electron spin qubits in semiconductor quantum dots. We weakly couple two electron spins to the ends of a two-site spin chain. Depending on the spin state of the chain, we observe oscillations between the distant end spins. We resolve the dynamics of both the end spins and the chain itself, and our measurements agree with simulations. Superexchange is a promising technique to create long-distance coupling between quantum-dot spin qubits.