As the energy relaxation time of superconducting qubits steadily improves, nonequilibrium quasiparticle excitations above the superconducting gap emerge as an increasingly relevant limit for qubit coherence. We measure fluctuations in the number of quasiparticle excitations by continuously monitoring the spontaneous quantum jumps between the states of a fluxonium qubit, in conditions where relaxation is dominated by quasiparticle loss. Resolution on the scale of a single quasiparticle is obtained by performing quantum nondemolition projective measurements within a time interval much shorter than $T_1$, using a quantum-limited amplifier (Josephson parametric converter). The quantum jump statistics switches between the expected Poisson distribution and a non-Poissonian one, indicating large relative fluctuations in the quasiparticle population, on time scales varying from seconds to hours. This dynamics can be modified controllably by injecting quasiparticles or by seeding quasiparticle-trapping vortices by cooling down in a magnetic field.

The magnetic ground state of the $J_{\text{eff}}=1/2$ hyperkagome lattice in ${\mathrm{Na}}_4{\mathrm{Ir}}_3{\mathrm{O}}_8$ is explored via combined bulk magnetization, muon spin relaxation, and neutron scattering measurements. A short-range, frozen state comprised of quasistatic moments develops below a characteristic temperature of $T_F=6\mathrm{K}$, revealing an inhomogeneous distribution of spins occupying the entirety of the sample volume. Quasistatic, short-range spin correlations persist until at least 20 mK and differ substantially from the nominally dynamic response of a quantum spin liquid. Our data demonstrate that an inhomogeneous magnetic ground state arises in ${\mathrm{Na}}_4{\mathrm{Ir}}_3{\mathrm{O}}_8$ driven either by disorder inherent to the creation of the hyperkagome lattice itself or stabilized via quantum fluctuations.

We study consequences of long-range elasticity in thermally assisted dynamics of yield stress materials. Within a two-dimensional mesoscopic model we calculate the mean-square displacement and the dynamical structure factor for tracer particle trajectories. The ballistic regime at short time scales is associated with a compressed exponential decay in the dynamical structure factor, followed by a subdiffusive crossover prior to the onset of diffusion. We relate this crossover to spatiotemporal correlations and thus go beyond established mean field predictions.

The Skyrme model has two Skyrmion solutions of baryon number 12, with $D_{3h}$ and $D_{4h}$ symmetries. The first has an equilateral triangular shape and the second an extended linear shape, analogous to the triangle and linear chain structures of three alpha particles. We recalculate the moments of inertia of these Skyrmions, and deduce the energies and spins of their quantized rotational excitations. There is a good match with the ground-state band of carbon-12, and with the recently established rotational band of the Hoyle state. The ratio of the root mean square matter radii also matches the experimental value.

We present the first measurement at the LHC of exclusive $J/\psi$ photoproduction off protons, in ultraperipheral proton-lead collisions at $\sqrt{s_{\text{NN}}}=5.02\mathrm{TeV}$. Events are selected with a dimuon pair produced either in the rapidity interval, in the laboratory frame, $2.5<y<4$ ($p\text{−}\mathrm{Pb}$) or $-3.6<y<-2.6$ ($\mathrm{Pb}\text{−}p$), and no other particles observed in the ALICE acceptance. The measured cross sections $\sigma (\gamma +p\to J/\psi +p)$ are $33.2\pm 2.2(\text{stat})\pm 3.2(\text{syst})\pm 0.7(\text{theor})\mathrm{nb}$ in $p\text{−}\mathrm{Pb}$ and $284\pm 36(\text{stat}{)}_{-32}^{+27}(\text{syst})\pm 26(\text{theor})\mathrm{nb}$ in $\mathrm{Pb}\text{−}p$ collisions. We measure this process up to about 700 GeV in the $\gamma p$ center of mass, which is a factor of two larger than the highest energy studied at HERA. The data are consistent with a power law dependence of the $J/\psi$ photoproduction cross section in $\gamma p$ energies from about 20 to 700 GeV, or equivalently, from Bjorken $x$ scaling variable between $\sim 2\times {10}^{-2}$ and $\sim 2\times {10}^{-5}$, thus indicating no significant change in the gluon density behavior of the proton between HERA and LHC energies.

We present a precise measurement of double-polarization asymmetries in the ${}^3\overrightarrow{\mathrm{He}}(\overrightarrow{\mathrm{e}},e^{\prime }d)$ reaction. This particular process is a uniquely sensitive probe of hadron dynamics in ${}^3\mathrm{He}$ and the structure of the underlying electromagnetic currents. The measurements have been performed in and around quasielastic kinematics at $Q^2=0.25(\mathrm{GeV}/c{)}^2$ for missing momenta up to $270\mathrm{MeV}/c$. The asymmetries are in fair agreement with the state-of-the-art calculations in terms of their functional dependencies on $p_{\mathit{m}}$ and $\omega$, but are systematically offset. Beyond the region of the quasielastic peak, the discrepancies become even more pronounced. Thus, our measurements have been able to reveal deficiencies in the most sophisticated calculations of the three-body nuclear system, and indicate that further refinement in the treatment of their two-and/or three-body dynamics is required.

Flatband networks are characterized by the coexistence of dispersive and flatbands. Flatbands (FBs) are generated by compact localized eigenstates (CLSs) with local network symmetries, based on destructive interference. Correlated disorder and quasiperiodic potentials hybridize CLSs without additional renormalization, yet with surprising consequences: (i) states are expelled from the FB energy $E_{\mathrm{FB}}$, (ii) the localization length of eigenstates vanishes as $\xi \sim 1/\ln (E-E_{\mathrm{FB}})$, (iii) the density of states diverges logarithmically (particle-hole symmetry) and algebraically (no particle-hole symmetry), and (iv) mobility edge curves show algebraic singularities at $E_{\mathrm{FB}}$. Our analytical results are based on perturbative expansions of the CLSs and supported by numerical data in one and two lattice dimensions.

We have performed high-resolution angle-resolved photoemission spectroscopy on an FeSe superconductor ($T_c\sim 8\mathrm{K}$), which exhibits a tetragonal-to-orthorhombic structural transition at $T_s\sim 90\mathrm{K}$. At low temperature, we found splitting of the energy bands as large as 50 meV at the $M$ point in the Brillouin zone, likely caused by the formation of electronically driven nematic states. This band splitting persists up to $T\sim 110\mathrm{K}$, slightly above $T_s$, suggesting that the structural transition is triggered by the electronic nematicity. We have also revealed that at low temperature the band splitting gives rise to a van Hove singularity within 5 meV of the Fermi energy. The present result strongly suggests that this unusual electronic state is responsible for the unconventional superconductivity in FeSe.

We adapt belief-propagation techniques to study the equilibrium behavior of a bipartite spin glass, with interactions between two sets of $N$ and $P=\alpha N$ spins each having an arbitrary degree, i.e., number of interaction partners in the opposite set. An equivalent view is then of a system of $N$ neurons storing $P$ diluted patterns via Hebbian learning, in the high storage regime. Our method allows analysis of parallel pattern processing on a broad class of graphs, including those with pattern asymmetry and heterogeneous dilution; previous replica approaches assumed homogeneity. We show that in a large part of the parameter space of noise, dilution, and storage load, delimited by a critical surface, the network behaves as an extensive parallel processor, retrieving all $P$ patterns in parallel without falling into spurious states due to pattern cross talk, as would be typical of the structural glassiness built into the network. Parallel extensive retrieval is more robust for homogeneous degree distributions, and is not disrupted by asymmetric pattern distributions. For scale-free pattern degree distributions, Hebbian learning induces modularity in the neural network; thus, our Letter gives the first theoretical description for extensive information processing on modular and scale-free networks.

We present a general and formally exact method to obtain the canonical one-body density distribution and the canonical free energy from direct decomposition of classical density functional results in the grand ensemble. We test the method for confined one-dimensional hard-core particles for which the exact grand potential density functional is explicitly known. The results agree to within high accuracy with those from exact methods and our Monte Carlo many-body simulations. The method is relevant for treating finite systems and for dynamical density functional theory.

It is well known that liquids confined to small nanoscopic pores and droplets exhibit thermal behavior very different from bulk samples. Less is known about liquids spontaneously confined through self-assembly into micellar structures. Here we demonstrate, using a very well-defined n-alkyl-poly(ethylene oxide) polymer system with a tunable structure, that $n$-alkane(s) forming 2–3 nm small micellar cores are affected considerably by confinement in the form of melting point depressions. Moreover, comparing the reduction in melting points, $\mathrm{\Delta }{T}_m$, determined through volumetric and calorimetric methods with the micellar core radius, $R_c$, obtained from small-angle x-ray scattering, we find excellent agreement with the well-known Gibbs-Thomson equation, $\mathrm{\Delta }{T}_m\sim R_c^{-1}$. This demonstrates that the reduced size, i.e., the Laplace pressure, is the dominant parameter governing the melting point depression in micellar systems.

The method for the computation of the conditional probability density function for the nonlinear Schrödinger equation with additive noise is developed. We present in a constructive form the conditional probability density function in the limit of small noise and analytically derive it in a weakly nonlinear case. The general theory results are illustrated using fiber-optic communications as a particular, albeit practically very important, example.

The $p_T$-differential production cross sections of the prompt charmed mesons $D^0$, $D^{+}$, $D^{*+}$, and $D_s^{+}$ and their charge conjugate in the rapidity interval $-0.96<y_{\text{cms}}<0.04$ were measured in $p\text{−}\mathrm{Pb}$ collisions at a center-of-mass energy $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ with the ALICE detector at the LHC. The nuclear modification factor $R_{p\mathrm{Pb}}$, quantifying the $D$-meson yield in $p\text{−}\mathrm{Pb}$ collisions relative to the yield in $pp$ collisions scaled by the number of binary nucleon-nucleon collisions, is compatible within the 15%–20% uncertainties with unity in the transverse momentum interval $1<p_T<24\mathrm{GeV}/c$. No significant difference among the $R_{p\mathrm{Pb}}$ of the four $D$-meson species is observed. The results are described within uncertainties by theoretical calculations that include initial-state effects. The measurement adds experimental evidence that the modification of the momentum spectrum of $D$ mesons observed in Pb-Pb collisions with respect to $pp$ collisions is due to strong final-state effects induced by hot partonic matter.

Spin relaxation based nuclear magnetic resonance (NMR) methods have been used extensively to determine pore size distributions in a variety of materials. This approach is based on the assumption that each pore is in the fast diffusion limit but that diffusion between pores can be neglected. However, in complex materials these assumptions may be violated and the relaxation time distribution is not easily interpreted. We present a 2D NMR technique and an associated data analysis that allow us to work directly with the time dependent experimental data without Laplace inversion to identify the signature of diffusive coupling between different pores. Measurements on microporous glass beads and numerical simulations are used to illustrate the technique.

We present a combined experimental and computational first-principles study of the superionic and structural properties of ${\mathrm{CaF}}_2$ at high $P-T$ conditions. We observe an anomalous superionic behavior in the low-$P$ fluorite phase that consists of a decrease of the normal $\to$ superionic critical temperature with compression. This unexpected effect can be explained in terms of a $P$-induced softening of a zone-boundary $X$ phonon that involves exclusively fluorine displacements. Also we find that superionic conductivity is absent in the high-$P$ cotunnite phase. Instead, superionicity develops in a new low-symmetry high-$T$ phase that we identify as monoclinic (space group $P{2}_1/c$). We discuss the possibility of observing these intriguing phenomena in related isomorphic materials.

Spin fluctuations were studied over a wide momentum ($\hslash Q$) and energy ($E$) space in the frustrated $d$-electron heavy-fermion metal ${\mathrm{LiV}}_2{\mathrm{O}}_4$ by time-of-flight inelastic neutron scattering. We observed the overall $Q-E$ evolutions near the characteristic $Q=0.6{\AA }^{-1}$ peak and found another weak broad magnetic peak around $2.4{\AA }^{-1}$. The data are described by a simple response function, a partially delocalized magnetic form factor, and antiferromagnetic short-range spatial correlations, indicating that heavy-fermion formation is attributable to spin-orbit fluctuations with orbital hybridization.

Error-correcting codes protect quantum information and form the basis of fault-tolerant quantum computing. Leading proposals for fault-tolerant quantum computation require codes with an exceedingly rare property, a transversal non-Clifford gate. Codes with the desired property are presented for $d$-level qudit systems with prime $d$. The codes use $n=d-1$ qudits and can detect up to $\sim d/3$ errors. We quantify the performance of these codes for one approach to quantum computation known as magic-state distillation. Unlike prior work, we find performance is always enhanced by increasing $d$.