Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for $H\to \text{invisible}$ decays where $H$ is produced according to the standard model via vector boson fusion, $Z(\ell \ell )H$, and $W/Z(\mathrm{had})H$, all performed with the ATLAS detector using $36.1{\mathrm{fb}}^{-1}$ of $pp$ collisions at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$ at the LHC. In combination with the results at $\sqrt{s}=7$ and 8 TeV, an exclusion limit on the $H\to \text{invisible}$ branching ratio of $0.26(0.17_{-0.05}^{+0.07})$ at 95% confidence level is observed (expected).

Electron-positron pair creation is considered when intense laser pulses collide head-on with $<1\mathrm{MeV}$ x-ray photons in the presence of stationary Coulomb charges $Z(-e)$. The analysis employs Coulomb-corrected Volkov states and is not limited to Born’s approximation in $Z$. The cross section and the yield increase dramatically with increasing $Z$, potentially enabling (i) measurable yields with petawatt lasers and (ii) sensitive tests of strong-field QED.

Ghost imaging is a quantum optics technique that uses correlations between two beams to reconstruct an image from photons that do not interact with the object being imaged. While pairwise (second-order) correlations are usually used to create the ghost image, higher-order correlations can be utilized to improve the performance. In this Letter, we demonstrate higher-order atomic ghost imaging, using entangled ultracold metastable helium atoms from an $s$-wave collision halo. We construct higher-order ghost images up to fifth order and show that using higher-order correlations can improve the visibility of the images without impacting the resolution. This is the first demonstration of higher-order ghost imaging with massive particles and the first higher-order ghost imaging protocol of any type using a quantum source.

We propose a scheme for continuously measuring the evolving quantum phase of a collective spin composed of $N$ pseudospins. Quantum nondemolition measurements of a lossy cavity mode interacting with an atomic ensemble are used to directly probe the phase of the collective atomic spin without converting it into a population difference. Unlike traditional Ramsey measurement sequences, our scheme allows for real-time tracking of time-varying signals. As a bonus, spin-squeezed states develop naturally, providing real-time phase estimation significantly more precise than the standard quantum limit of $\mathrm{\Delta }{\varphi }_{\mathrm{SQL}}=1/\sqrt{N}\mathrm{rad}$.

We study the current-carrying steady state of a transverse field Ising chain coupled to magnetic thermal reservoirs and obtain the nonequilibrium phase diagram as a function of the magnetization potential of the reservoirs. Upon increasing the magnetization bias we observe a discontinuous jump of the magnetic order parameter that coincides with a divergence of the correlation length. For steady states with a nonvanishing conductance, the entanglement entropy at zero temperature displays a bias dependent logarithmic correction that violates the area law and differs from the well-known equilibrium case. Our findings show that out-of-equilibrium conditions allow for novel critical phenomena not possible at equilibrium.

We consider a fractional quantum Hall bilayer system with an interface between quantum Hall states of filling fractions $({\nu }_{\mathrm{top}},{\nu }_{\text{bottom}})=(1,1)$ and $(1/3,2)$, motivated by a recent approach to engineering artificial edges [Y. Ronen et al., Nat. Phys. 14, 411 (2018)]. We show that random tunneling and strong repulsive interactions within one of the layers will drive the system to a stable fixed point with two counterpropagating charge modes which have attractive interactions. As a result, slowly decaying correlations on the edge become predominantly superconducting. We discuss the resulting observable effects and derive general requirements for electron attraction in Abelian quantum Hall states. The broader interest in fractional quantum Hall edge with quasi-long-range superconducting order lies in the prospects of hosting exotic anyonic boundary excitations, which may serve as a platform for topological quantum computation.

A chain of small Josephson junctions (a.k.a. superinductor) emerged recently as a high-inductance, low-loss element of superconducting quantum devices. We notice that the intrinsic parameters of a typical superinductor in fact place it into the Bose glass universality class for which the propagation of waves in a sufficiently long chain is hindered by pinning. Its weakness provides for a broad crossover from the spectrum of well-resolved plasmon standing waves at high frequencies to the low-frequency excitation spectrum of a pinned charge density wave. We relate the scattering amplitude of microwave photons reflected off a superinductor to the dynamics of a Bose glass. The dynamics at long and short scales compared to the Larkin pinning length determines the low- and high-frequency asymptotes of the reflection amplitude.

In equilibrium the interface potential that describes the interaction between two AB interfaces in a binary blend of $A$ and $B$ homopolymers is attractive at all distances, resulting in coarsening of the blend morphology even in the absence of interface curvature. We demonstrate that the dissipative assembly in response to a time-periodic variation of the blend incompatibility qualitatively alters this behavior; i.e., for suitable parameters the interface potential exhibits a periodic spatial modulation and AB interfaces adopt a well-defined distance. We explore for which oscillation periods and amplitudes an interface repulsion occurs and demonstrate that we can control the preferred interface distance over a wide range by varying the oscillation period. Using particle-based simulations we explicitly demonstrate that this dissipative assembly of a homopolymer blend results in a lamellar structure with multiple planar interfaces in a thin film geometry.

We develop an extension of the variational quantum eigensolver (VQE) algorithm—multistate contracted VQE (MC-VQE)—that allows for the efficient computation of the transition energies between the ground state and several low-lying excited states of a molecule, as well as the oscillator strengths associated with these transitions. We numerically simulate MC-VQE by computing the absorption spectrum of an ab initio exciton model of an 18-chromophore light-harvesting complex from purple photosynthetic bacteria.

Inspired by the similarity between the fractal Weierstrass function and quantum systems with discrete scaling symmetry, we establish general conditions under which the dynamics of a quantum system will exhibit fractal structure in the time domain. As an example, we discuss the dynamics of the Loschmidt amplitude and the zero-momentum occupation of a single particle moving in a scale invariant $1/r^2$ potential. In order to show these conditions can be realized in ultracold atomic gases, we perform numerical simulations with practical experimental parameters, which shows that the dynamical fractal can be observed in realistic timescales. The predication can be directly verified in current cold atom experiments.

Critical phenomena in gravitational collapse exhibit the universal features of self-similarity, critical scaling, and the appearance of a naked singularity. We study critical collapse in anti–de Sitter space, focusing on holographic field theory observables. We demonstrate that the echoing period, critical exponent, and signatures of the naked singularity can all be extracted from the holographic stress tensor.

We analyzed a 6.7-yr span of data from a rotating torsion-pendulum containing $\approx {10}^{23}$ polarized electrons to search for the “wind” arising from ultralight, axionlike dark matter with masses between ${10}^{-23}$ and ${10}^{-18}\mathrm{eV}/c^2$. Over much of this range we set a 95% confidence limit $F_a/C_{\mathrm{e}}>2\times {10}^{15}\mathrm{eV}$ on the axionlike decay constant.

We formulate Nielsen’s geometric approach to circuit complexity in the context of two-dimensional conformal field theories, where series of conformal transformations are interpreted as “unitary circuits” built from energy-momentum tensor gates. We show that the complexity functional in this setup can be written as the Polyakov action of two-dimensional gravity or, equivalently, as the geometric action on the coadjoint orbits of the Virasoro group. This way, we argue that gravity sets the rules for optimal quantum computation in conformal field theories.

We present a closed expression for the octagon form factor which appears as a building block in a class of four-point correlation functions in $\mathcal{N}=4$ supersymmetric Yang-Mills theory considered recently by Coronado. The octagon form factor is expressed, to all loop orders, as the determinant of a semi-infinite matrix. We find that perturbatively at weak coupling the entries of this matrix are linear combinations of ladder functions with simple rational coefficients.

We report a fuel-dependent reactor electron antineutrino (${\overline{\nu }}_e$) yield using six $2.8{\mathrm{GW}}_{\mathrm{th}}$ reactors in the Hanbit nuclear power plant complex, Yonggwang, Korea. The analysis uses 850 666 ${\overline{\nu }}_e$ candidate events with a background fraction of 2.0% acquired through inverse beta decay (IBD) interactions in the near detector for 1807.9 live days from August 2011 to February 2018. Based on multiple fuel cycles, we observe a fuel ${}^{235}\mathrm{U}$ dependent variation of measured IBD yields with a slope of $(1.51\pm 0.23)\times {10}^{-43}{\mathrm{cm}}^2/\mathrm{fission}$ and measure a total average IBD yield of $(5.84\pm 0.13)\times {10}^{-43}{\mathrm{cm}}^2/\mathrm{fission}$. The hypothesis of no fuel-dependent IBD yield is ruled out at $6.6\sigma$. The observed IBD yield variation over ${}^{235}\mathrm{U}$ isotope fraction does not show significant deviation from the Huber-Mueller (HM) prediction at $1.3\sigma$. The measured fuel-dependent variation determines IBD yields of $(6.15\pm 0.19)\times {10}^{-43}$ and $(4.18\pm 0.26)\times {10}^{-43}{\mathrm{cm}}^2/\mathrm{fission}$ for two dominant fuel isotopes ${}^{235}\mathrm{U}$ and ${}^{239}\mathrm{Pu}$, respectively. The measured IBD yield per ${}^{235}\mathrm{U}$ fission shows the largest deficit relative to the HM prediction. Reevaluation of the ${}^{235}\mathrm{U}$ IBD yield per fission may mostly solve the reactor antineutrino anomaly (RAA) while ${}^{239}\mathrm{Pu}$ is not completely ruled out as a possible contributor to the anomaly. We also report a $2.9\sigma$ correlation between the fractional change of the 5 MeV excess and the reactor fuel isotope fraction of ${}^{235}\mathrm{U}$.

We demonstrate single-photon superradiance from artificially constructed nonbonded zinc-phthalocyanine molecular chains of up to 12 molecules. We excite the system via electron tunneling in a plasmonic nanocavity and quantitatively investigate the interaction of the localized plasmon with single-exciton superradiant states resulting from dipole-dipole coupling. Dumbbell-like patterns obtained by subnanometer resolved spectroscopic imaging disclose the coherent nature of the coupling associated with superradiant states while second-order photon correlation measurements demonstrate single-photon emission. The combination of spatially resolved spectral measurements with theoretical considerations reveals that nanocavity plasmons dramatically modify the linewidth and intensity of emission from the molecular chains, but they do not dictate the intrinsic coherence of the superradiant states. Our studies shed light on the optical properties of molecular collective states and their interaction with nanoscopically localized plasmons.

The standard entanglement test using the Clauser-Horne-Shimony-Holt inequality is known to fail in mesoscopic junctions at finite temperatures. Since this is due to the bidirectional particle flow, a similar failure is expected to occur in an ac-driven contact. We develop a continuous-variable entanglement test suitable for electrons and holes that are created by the ac drive. At low enough temperatures the generalized Bell inequality is violated in junctions with low conductance or a small number of transport channels and with ac voltages which create few electron-hole pairs per cycle. Our ac-entanglement test depends on the total number of electron-hole pairs and on the distribution of probabilities of pair creations similar to the Fano factor.

Metabolism and evolution are closely connected: if a mutation incurs extra energetic costs for an organism, there is a baseline selective disadvantage that may or may not be compensated for by other adaptive effects. A long-standing, but to date unproven, hypothesis is that this disadvantage is equal to the fractional cost relative to the total resting metabolic expenditure. We validate this result from physical principles through a general growth model and show it holds to excellent approximation for experimental parameters drawn from a wide range of species.