In a locally interacting many-body system, two isolated qubits, separated by a large distance $r$, become correlated and entangled with each other at a time $t\ge r/v$. This finite speed $v$ of quantum information scrambling limits quantum information processing, thermalization, and even equilibrium correlations. Yet most experimental systems contain long range power-law interactions—qubits separated by $r$ have potential energy $V(r)\propto r^{-\alpha }$. Examples include the long range Coulomb interactions in plasma ($\alpha =1$) and dipolar interactions between spins ($\alpha =3$). In one spatial dimension, we prove that the speed of quantum scrambling remains finite for sufficiently large $\alpha$. This result parametrically improves previous bounds, compares favorably with recent numerical simulations, and can be realized in quantum simulators with dipolar interactions. Our new mathematical methods lead to improved algorithms for classically simulating quantum systems, and improve bounds on environmental decoherence in experimental quantum information processors.

We address the question of verifying the quantumness of thermal machines. A Szilárd engine is truly quantum if its work output cannot be described by a local hidden state model, i.e., an objective local statistical ensemble. Quantumness in this scenario is revealed by a steering-type inequality which bounds the classically extractable work. A quantum Maxwell demon can violate that inequality by exploiting quantum correlations between the work medium and the thermal environment. While for a classical Szilárd engine an objective description of the medium always exists, any such description can be ruled out by a steering task in a truly quantum case.

We perform a global sensitivity analysis of the binding energy and the charge radius of the nucleus ${}^{16}\mathrm{O}$ to identify the most influential low-energy constants in the next-to-next-to-leading order chiral Hamiltonian with two- and three-nucleon forces. For this purpose, we develop a subspace-projected coupled-cluster method using eigenvector continuation [Frame D. et al., Phys. Rev. Lett. 121, 032501 (2018)]. With this method, we compute the binding energy and charge radius of ${}^{16}\mathrm{O}$ at more than $10^6$ different values of the 16 low-energy constants in one hour on a standard laptop computer. For relatively small subspace projections, the root-mean-square error is about 1% compared to full-space coupled-cluster results. We find that 58(1)% of the variance in energy can be apportioned to a single contact term in the ${}^3{S}_1$ wave, whereas the radius depends sensitively on several low-energy constants and their higher-order correlations. The results identify the most important parameters for describing nuclear saturation and help prioritize efforts for uncertainty reduction of theoretical predictions. The achieved acceleration opens up an array of computational statistics analyses of the underlying description of the strong nuclear interaction in nuclei across the Segrè chart.

We report the finding of “triply magic” conditions (the doubly magic frequency-intensity conditions of an optical dipole trap plus the magic magnetic field) for the microwave transitions of optically trapped alkali-metal atoms. The differential light shift (DLS) induced by a degenerate two-photon process is adopted to compensate a DLS associated with the one-photon process. Thus, doubly magic conditions for the intensity and frequency of the optical trap beam can be found. Moreover, the DLS decouples from the magnetic field in a linearly polarized optical dipole trap, so that the magic condition of the magnetic field can be applied independently. Therefore, the triply magic conditions can be realized simultaneously. We also experimentally demonstrate the doubly magic frequency-intensity conditions as well as the independence of the magnetic field. When the triply magic conditions are fulfilled, the inhomogeneous and homogeneous decoherences for the optically trapped atom will be dramatically suppressed, and the coherence time can be extended significantly.

Heat dissipation still remains an unsolved problem in dynamic plasticity, where nearly adiabatic conditions prevail during high-rate loading scenarios. It is well known that the mechanical energy that is not dissipated as heat during material straining remains stored in the lattice as microstructural defects, and thus, a one-to-one relationship can be expected between the stored energy, the materials microstructure, and its mechanical characteristics. This work demonstrates that this is not so straightforward. High-rate experiments on a Kolsky bar, combined with in situ thermal measurements, were performed on two well-studied materials: pure nickel and aluminum. A dislocation-based constitutive model was used to estimate the mechanical and thermomechanical material behavior. For both materials, the thermal response was observed to be strongly strain rate sensitive, while the mechanical flow, and microstructural characteristics (as characterized by transmission electron microscopy at similar strains), were not. This apparent discrepancy between mechanical and microstructural vs thermal results is discussed, and the concept of thermomechanical conversion is reassessed.

Temperature gradients can change the concentration distribution in multicomponent materials. This cross-coupling effect of heat and mass transfer is difficult to measure in liquid alloys. We present a new method using x-ray radiography in combination with a high temperature furnace to measure thermodiffusion in melts time and space resolved. This greatly improves the process control and allows us to determine diffusion and thermodiffusion simultaneously. In a first experiment we demonstrate that in liquid ${\mathrm{Al}}_{78.5}{\mathrm{Ni}}_{21.5}$ the component nickel diffuses to the cold end of the sample with a Soret coefficient on the order of ${10}^{-3}{\mathrm{K}}^{-1}$.

Intrigued by the discovery of high-temperature superconductivity in a single unit-cell layer of FeSe film on ${\mathrm{SrTiO}}_3$, researchers recently found large superconductinglike energy gaps in K-adsorbed multilayer FeSe films by angle-resolved photoemission and scanning tunneling spectroscopy. However, the existence and nature of the high-temperature superconductivity inferred by the spectroscopic studies has not been investigated by measurements of zero resistance or the Meissner effect due to the fragility of K atoms in air. Using a self-developed multifunctional scanning tunneling microscope, we succeed in observing the diamagnetic response of K-adsorbed multilayer FeSe films, and thus find a dome-shaped relation between the critical temperature ($T_c$) and K coverage. Intriguingly, $T_c$ exhibits an approximately linear dependence on the superfluid density in the whole K adsorbed region. Moreover, the quadratic low-temperature variation in the London penetration depth indicates a sign-reversal order parameter. These results provide compelling information towards further understanding of the high-temperature superconductivity in FeSe-derived superconductors.

We derive fundamental per-channel bounds on angle-integrated absorption and thermal radiation for arbitrarily structured bodies—for any given material susceptibility and bounding region—that simultaneously encode both the per-volume limit on polarization set by passivity and geometric constraints on radiative efficiencies set by finite object sizes through the scattering $\mathbb{T}$ operator. We then analyze these bounds in two practical settings, comparing against prior limits as well as near optimal structures discovered through topology optimization. Principally, we show that the bounds properly capture the physically observed transition from the volume scaling of absorptivity seen in deeply subwavelength objects (nanoparticle radius or thin film thickness) to the area scaling of absorptivity seen in ray optics (blackbody limits).

One of the biggest unresolved problems in crystallization phenomena is the significant discrepancy in the nucleation rate between experiments and simulations even for the simplest liquid, i.e., the hard-sphere system. A popular explanation for this discrepancy is the neglect of hydrodynamic interactions (HI) in simulation studies. By comparing simulations with and without HI, we show that the long-time diffusive dynamics of the colloids is slowed down more rapidly by hydrodynamic lubrication effects with increasing volume fraction. We find that the kinetics of both nucleation and growth are controlled by this long-time diffusion and that it is possible to account for most of the effects of HI by rescaling with this timescale. Therefore, we conclude that HI is not the primary cause of the accelerated nucleation rates observed in experiments.

Bacterial biofilms represent a major form of microbial life on Earth and serve as a model active nematic system, in which activity results from growth of the rod-shaped bacterial cells. In their natural environments, ranging from human organs to industrial pipelines, biofilms have evolved to grow robustly under significant fluid shear. Despite intense practical and theoretical interest, it is unclear how strong fluid flow alters the local and global architectures of biofilms. Here, we combine highly time-resolved single-cell live imaging with 3D multiscale modeling to investigate the mechanisms by which flow affects the dynamics of all individual cells in growing biofilms. Our experiments and cell-based simulations reveal three quantitatively different growth phases in strong external flow and the transitions between them. In the initial stages of biofilm development, flow induces a downstream gradient in cell orientation, causing asymmetrical dropletlike biofilm shapes. In the later developmental stages, when the majority of cells are sheltered from the flow by the surrounding extracellular matrix, buckling-induced cell verticalization in the biofilm core restores radially symmetric biofilm growth, in agreement with predictions of a 3D continuum model.

The magnetized solar wind modulates the Galactic cosmic ray flux in the heliosphere up to rigidities as high as 40 GeV. In this work, we present a new and straightforward extension of the popular but limited force-field model, thus providing a fast and robust method for phenomenological studies of Galactic cosmic rays. Our semianalytical approach takes into account charge-sign dependent modulation due to drifts in the heliospheric magnetic field and has been validated via comparison to a fully numerical code. Our model nicely reproduces the time-dependent AMS-02 measurements and we find the strength of diffusion and drifts to be strongly correlated with the heliospheric tilt angle and magnitude of the magnetic field. We are able to predict the electron and positron fluxes beyond the range for which measurements by AMS-02 have been presented. We have made an example script for the semianalytical model publicly available and we urge the community to adopt this approach for phenomenological studies.

We develop a rigorous theoretical approach for analyzing inelastic scattering of photon pairs in arrays of two-level qubits embedded into a waveguide. Our analysis reveals a strong enhancement of the scattering when the energy of incoming photons resonates with the double-excited subradiant states. We identify the role of different double-excited states in the scattering, such as superradiant, subradiant, and twilight states, as a product of single-excitation bright and subradiant states. Importantly, the $N$-excitation subradiant states can be engineered only if the number of qubits exceeds $2N$. Both the subradiant and twilight states can generate long-lived photon-photon correlations, paving the way to storage and processing of quantum information.

We experimentally demonstrate flipping the phase state of a parametron within a single period of its oscillation. A parametron is a binary logic element based on a driven nonlinear resonator. It features two stable phase states that define an artificial spin. The most basic operation performed on a parametron is a bit flip between these two states. Thus far, this operation involved changing the energetic population of the resonator and therefore required a number of oscillations on the order of the quality factor $Q$. Our technique takes a radically different approach and relies on rapid control of the underlying potential. Our work represents a paradigm shift for phase-encoded logic operations by boosting the speed of a parametron bit flip to its ultimate limit.

The existence of the edge states at the interface between two media with different topological properties is protected by symmetry, which makes such states robust against structural defects or disorder. We show that, if a system supports more than one topological edge state at the interface, even a weak periodic deformation may scatter one edge state into another without coupling to bulk modes. This is the Bragg scattering of the edge modes, which in a topological system is highly selective, with closed bulk and backward scattering channels, even when conditions for resonant scattering are not satisfied. When such a system bears nonlinearity, Bragg scattering enables the formation of a new type of soliton—topological Bragg solitons. We report them in a spin-orbit-coupled (SOC) Bose-Einstein condensate in a homogeneous honeycomb Zeeman lattice. An interface supporting two edge states is created by two different SOCs, with the $y$ component of the synthetic magnetic field having opposite directions at different sides of the interface. The reported Bragg solitons are found to be stable.

Orientation-dependent aloof-beam vibrational electron-energy-loss spectroscopy is carried out on uniaxial icosahedral ${\mathrm{B}}_{12}{\mathrm{P}}_2$ submicron crystals. We demonstrate that the high sensitivity of the signal to the crystal orientation allows for an unambiguous determination of the symmetry of normal modes occurring at the Brillouin zone center of this anisotropic compound. The experimental results are assessed using first-principles quantum mechanical calculations (density functional theory) of the dielectric response of the specimen. The high spatial resolution inherent to this technique when implemented in the transmission electron microscope thus opens the door to nanoscale orientation-dependent vibrational spectroscopy.

We study quantum metrology for unitary dynamics. Analytic solutions are given for both the optimal unitary state preparation starting from an arbitrary mixed state and the corresponding optimal measurement precision. This represents a rigorous generalization of known results for optimal initial states and upper bounds on measurement precision which can only be saturated if pure states are available. In particular, we provide a generalization to mixed states of an upper bound on measurement precision for time-dependent Hamiltonians that can be saturated with optimal Hamiltonian control. These results make precise and reveal the full potential of mixed states for quantum metrology.