Layers of two-dimensional materials stacked with a small twist angle give rise to beating periodic patterns on a scale much larger than the original lattice, referred to as a “moiré superlattice.” Here, we demonstrate a higher-order “moiré of moiré” superlattice in twisted trilayer graphene with two consecutive small twist angles. We report correlated insulating states near the half filling of the moiré of moiré superlattice at an extremely low carrier density ($\sim {10}^{10}{\mathrm{cm}}^{-2}$), near which we also report a zero-resistance transport behavior typically expected in a 2D superconductor. The full-occupancy ($\nu =-4$ and $\nu =4$) states are semimetallic and gapless, distinct from the twisted bilayer systems.

Fluorine is one of the most interesting elements in nuclear astrophysics, where the ${}^{19}\mathrm{F}(p,\alpha ){}^{16}\mathrm{O}$ reaction is of crucial importance for Galactic ${}^{19}\mathrm{F}$ abundances and CNO cycle loss in first generation Population III stars. As a day-one campaign at the Jinping Underground Nuclear Astrophysics experimental facility, we report direct measurements of the essential ${}^{19}\mathrm{F}(p,\alpha \gamma ){}^{16}\mathrm{O}$ reaction channel. The $\gamma$-ray yields were measured over $E_{\mathrm{c}.\mathrm{m}.}=72.4–344\mathrm{keV}$, covering the Gamow window; our energy of 72.4 keV is unprecedentedly low, reported here for the first time. The experiment was performed under the extremely low cosmic-ray-induced background environment of the China JinPing Underground Laboratory, one of the deepest underground laboratories in the world. The present low-energy $S$ factors deviate significantly from previous theoretical predictions, and the uncertainties are significantly reduced. The thermonuclear ${}^{19}\mathrm{F}(p,\alpha \gamma ){}^{16}\mathrm{O}$ reaction rate has been determined directly at the relevant astrophysical energies.

We demonstrate, theoretically, how the insertion of an enhanced epsilon-near-zero (EENZ) mirror in a laser cavity grants exceptional control over the coherence properties of the emitted light beam. By exploiting the peculiar sensitivity to polarization of EENZ materials, we achieve superior control over the spatial coherence of the emitted laser light, which can be switched at will between nearly incoherent and fully coherent, solely by means of polarization optics. Our EENZ cavity design is expected to be an efficient, compact, reconfigurable, and easily scalable source of light for illumination and speckle contrast imaging, as well as any other application that benefits from controlled spatial coherence.

We theoretically demonstrate the possibility of inversion of solvent migration in charged membranes, opposing osmosis. Inversion of solvent migration is ascribed to the finite volume of ions in the solution permeating the membrane, a quantity that has been neglected in the literature so far. We propose a model of the electrochemistry in the proximity of an electrode, illustrating the range of the molar volume of ions that can yield the inversion of solvent migration. This study poses the basis for novel applications in microfluidics, nanofluidics, and electrochemistry, along with new inquiries in biology.

Magnetoresistance of the correlated narrow-gap semiconductor FeSi was investigated by the radio frequency self-resonant spiral coil technique in magnetic fields up to 500 T, which is supplied by an electromagnetic flux compression megagauss generator. Semiconductor-to-metal transition accomplishes around 270 T observed as a sharp kink in the magnetoresistance, which implies the closing of the hybridization gap by the Zeeman shift of band edges. In the temperature-magnetic field phase diagram, the semiconductor-metal transition field is found to be almost independent of temperature, which is in contrast to a characteristic magnetic field associated with the hopping magnetoconduction in the in-gap localized states, exhibiting a notable temperature dependence.

The study of high-velocity particle-laden flow interactions is of importance for the understanding of a wide range of natural phenomena, ranging from planetary formation to cloud interactions. Experimental observations of particle dynamics are sparse given the difficulty of generating high-velocity flows of many particles. Ejecta microjets are micron-scale jets formed by strong shocks interacting with imprinted surfaces to generate particle plumes traveling at several kilometers per second. As such, the interaction of two ejecta microjets provides a novel experimental methodology to study interacting particle streams. In this Letter, we report the first time sequences of x-ray radiography images of two interacting tin ejecta microjets taken on a platform designed for the OMEGA Extended Performance (OMEGA EP) laser. We observe that the microjets pass through each other unattenuated for the case of $11.7\pm 3.2\mathrm{GPa}$ shock pressures and jet velocities of $2.2\pm 0.5\mathrm{km}/\mathrm{s}$ but show strong interaction dynamics for $116.0\pm 6.1\mathrm{GPa}$ shock pressures and jet velocities of $6.5\pm 0.5\mathrm{km}/\mathrm{s}$. We find that radiation-hydrodynamic simulations of the experiments are able to capture many aspects of the collisional behavior, such as the attenuation of jet velocity in the direction of propagation, but are unable to match the full spread of the strongly interacting cloud.

The mechanical properties of soft materials can be probed on small length scales by microrheology. A common approach tracks fluctuations of micrometer-sized beads embedded in the medium to be characterized. This approach yields results that depend on probe size when the medium has structure on comparable length scales. Here, we introduce filament-based microrheology using high-aspect-ratio semiflexible filaments as probes. Such quasi-1D probes are much less invasive than beads due to their small cross sections. Moreover, by imaging transverse bending modes, we simultaneously determine the micromechanical response of the medium on multiple length scales corresponding to the mode wavelengths. We use semiflexible single-walled carbon nanotubes as probes that can be accurately and rapidly imaged based on their stable near-IR fluorescence. We find that the viscoelastic properties of sucrose, polyethylene oxide, and hyaluronic acid solutions measured in this way are in good agreement with those measured by conventional micro- and macrorheology.

We present results from an analysis of all data taken by the BICEP2, Keck Array, and BICEP3 CMB polarization experiments up to and including the 2018 observing season. We add additional Keck Array observations at 220 GHz and BICEP3 observations at 95 GHz to the previous $95/150/220\mathrm{GHz}$ dataset. The $Q/U$ maps now reach depths of 2.8, 2.8, and $8.8\mu {\mathrm{K}}_{\mathrm{CMB}}\mathrm{arcmin}$ at 95, 150, and 220 GHz, respectively, over an effective area of $\approx 600$ square degrees at 95 GHz and $\approx 400$ square degrees at 150 and 220 GHz. The 220 GHz maps now achieve a signal-to-noise ratio on polarized dust emission exceeding that of Planck at 353 GHz. We take auto- and cross-spectra between these maps and publicly available WMAP and Planck maps at frequencies from 23 to 353 GHz and evaluate the joint likelihood of the spectra versus a multicomponent model of lensed $\mathrm{\Lambda }\mathrm{CDM}+r+\mathrm{dust}+\mathrm{synchrotron}+\mathrm{noise}$. The foreground model has seven parameters, and no longer requires a prior on the frequency spectral index of the dust emission taken from measurements on other regions of the sky. This model is an adequate description of the data at the current noise levels. The likelihood analysis yields the constraint $r_{0.05}<0.036$ at 95% confidence. Running maximum likelihood search on simulations we obtain unbiased results and find that $\sigma (r)=0.009$. These are the strongest constraints to date on primordial gravitational waves.

We propose and experimentally demonstrate a self-calibrating detector of Cooper pair depairing in a superconductor based on a mesoscopic superconducting island coupled to normal metal leads. On average, exactly one electron passes through the device per broken Cooper pair, independent of the absorber volume, device, or material parameters. The device operation is explained by a simple analytical model and verified with numerical simulations in quantitative agreement with experiment. In a proof-of-concept experiment, we use such a detector to measure the high-frequency phonons generated by another, electrically decoupled superconducting island, with a measurable signal resulting from less than 10 fW of dissipated power.

Periodically driven (Floquet) quantum systems have recently been a focus of nonequilibrium physics by virtue of their rich dynamics. Time-periodic systems not only exhibit symmetries that resemble those in spatially periodic systems, but also display novel behavior that arises from symmetry breaking. Characterization of such dynamical symmetries is crucial, but often challenging due to limited driving strength and lack of an experimentally accessible characterization technique. Here, we show how to reveal dynamical symmetries, namely, parity, rotation, and particle-hole symmetries, by observing symmetry-induced Floquet selection rules. Notably, we exploit modulated driving to reach the strong light-matter coupling regime, and we introduce a protocol to experimentally extract the transition matrix elements between Floquet states from the system coherent evolution. By using nitrogen-vacancy centers in diamond as an experimental test bed, we execute our protocol to observe symmetry-protected dark states and dark bands, and coherent destruction of tunneling. Our work shows how one can exploit the quantum control toolkit to study dynamical symmetries that arise in the topological phases of strongly driven Floquet systems.

Despite a long history of studies, acoustic waves are generally regarded as spinless scalar waves, until recent research revealed their rich structures. Here, we report the experimental observation of skyrmion configurations in acoustic waves. We find that surface acoustic waves trapped by a designed hexagonal acoustic metasurface give rise to skyrmion lattice patterns in the dynamic acoustic velocity fields (i.e., the oscillating acoustic air flows). Using an acoustic velocity sensing technique, we directly visualize a Néel-type skyrmion configuration of the acoustic velocity fields. We further demonstrate, respectively, the controllability and robustness of the acoustic skyrmion lattices by tuning the phase differences between the acoustic sources and by introducing local perturbations in our setup. Our study unveils a fundamental acoustic phenomenon that may enable unprecedented manipulation of acoustic waves and may inspire future technologies including advanced acoustic tweezers for the control of small particles.

We analyze the performance of a quantum computer architecture combining a small processor and a storage unit. By focusing on integer factorization, we show a reduction by several orders of magnitude of the number of processing qubits compared with a standard architecture using a planar grid of qubits with nearest-neighbor connectivity. This is achieved by taking advantage of a temporally and spatially multiplexed memory to store the qubit states between processing steps. Concretely, for a characteristic physical gate error rate of ${10}^{-3}$, a processor cycle time of 1 microsecond, factoring a 2 048-bit RSA integer is shown to be possible in 177 days with 3D gauge color codes assuming a threshold of 0.75% with a processor made with 13 436 physical qubits and a memory that can store 28 million spatial modes and 45 temporal modes with 2 hours’ storage time. By inserting additional error-correction steps, storage times of 1 second are shown to be sufficient at the cost of increasing the run-time by about 23%. Shorter run-times (and storage times) are achievable by increasing the number of qubits in the processing unit. We suggest realizing such an architecture using a microwave interface between a processor made with superconducting qubits and a multiplexed memory using the principle of photon echo in solids doped with rare-earth ions.

Systems subject to a high-frequency drive can spend an exponentially long time in a prethermal regime, in which novel phases of matter with no equilibrium counterpart can be realized. Because of the notorious computational challenges of quantum many-body systems, numerical investigations in this direction have remained limited to one spatial dimension, in which long-range interactions have been proven a necessity. Here, we show that prethermal nonequilibrium phases of matter are not restricted to the quantum domain. Studying the Hamiltonian dynamics of a large three-dimensional lattice of classical spins, we provide the first numerical proof of prethermal phases of matter in a system with short-range interactions. Concretely, we find higher-order as well as fractional discrete time crystals breaking the time-translational symmetry of the drive with unexpectedly large integer as well as fractional periods. Our work paves the way toward the exploration of novel prethermal phenomena by means of classical Hamiltonian dynamics with virtually no limitations on the system’s geometry or size, and thus with direct implications for experiments.

We demonstrate that the prethermal regime of periodically driven (Floquet), classical many-body systems can host nonequilibrium phases of matter. In particular, we show that there exists an effective Hamiltonian that captures the dynamics of ensembles of classical trajectories despite the breakdown of this description at the single trajectory level. In addition, we prove that the effective Hamiltonian can host emergent symmetries protected by the discrete time-translation symmetry of the drive. The spontaneous breaking of such an emergent symmetry leads to a subharmonic response, characteristic of time crystalline order, that survives to exponentially late times in the frequency of the drive. To this end, we numerically demonstrate the existence of classical prethermal time crystals in systems with different dimensionalities and ranges of interaction. Extensions to higher order and fractional time crystals are also discussed.

In microtubule-based active nematics, motor-driven extensile motion of microtubule bundles powers chaotic large-scale dynamics. We quantify the interfilament sliding motion both in isolated bundles and in a dense active nematic. The extension speed of an isolated microtubule pair is comparable to the molecular motor stepping speed. In contrast, the net extension in dense 2D active nematics is significantly slower; the interfilament sliding speeds are widely distributed about the average and the filaments exhibit both contractile and extensile relative motion. These measurements highlight the challenge of connecting the extension rate of isolated bundles to the multimotor and multifilament interactions present in a dense 2D active nematic. They also provide quantitative data that is essential for building multiscale models.

A single quantum emitter can possess a very strong intrinsic nonlinearity, but its overall promise for nonlinear effects is hampered by the challenge of efficient coupling to incident photons. Common nonlinear optical materials, on the other hand, are easy to couple to but are bulky, imposing a severe limitation on the miniaturization of photonic systems. In this Letter, we show that a single organic molecule acts as an extremely efficient nonlinear optical element in the strong coupling regime of cavity quantum electrodynamics. We report on single-photon sensitivity in nonlinear signal generation and all-optical switching. Our work promotes the use of molecules for applications such as integrated photonic circuits operating at very low powers.

Detecting the faint emission of a secondary source in the proximity of the much brighter one has been the most severe obstacle for using direct imaging in searching for exoplanets. Using quantum state discrimination and quantum imaging techniques, we show that one can significantly reduce the probability of error for detecting the presence of a weak secondary source, especially when the two sources have small angular separations. If the weak source has intensity $\epsilon \ll 1$ relative to the bright source, we find that the error exponent can be improved by a factor of $1/\epsilon$. We also find linear-optical measurements that are optimal in this regime. Our result serves as a complementary method in the toolbox of optical imaging, with applications ranging from astronomy to microscopy.

The topology of quantum systems has become a topic of great interest since the discovery of topological insulators. However, as a hallmark of the topological insulators, the spin Chern number has not yet been experimentally detected. The challenge to directly measure this topological invariant lies in the fact that this spin Chern number is defined based on artificially constructed wave functions. Here we experimentally mimic the celebrated Bernevig-Hughes-Zhang model with cold atoms, and then measure the spin Chern number with the linear response theory. We observe that, although the Chern number for each spin component is ill defined, the spin Chern number measured by their difference is still well defined when both energy and spin gaps are nonvanished.

The scope of analog simulation in atomic, molecular, and optical systems has expanded greatly over the past decades. Recently, the idea of synthetic dimensions—in which transport occurs in a space spanned by internal or motional states coupled by field-driven transitions—has played a key role in this expansion. While approaches based on synthetic dimensions have led to rapid advances in single-particle Hamiltonian engineering, strong interaction effects have been conspicuously absent from most synthetic dimensions platforms. Here, in a lattice of coupled atomic momentum states, we show that atomic interactions result in large and qualitative changes to dynamics in the synthetic dimension. We explore how the interplay of nonlinear interactions and coherent tunneling enriches the dynamics of a one-band tight-binding model giving rise to macroscopic self-trapping and phase-driven Josephson dynamics with a nonsinusoidal current-phase relationship, which can be viewed as stemming from a nonlinear band structure arising from interactions.

The second layer of ${}^4\mathrm{He}$ films adsorbed on a graphite substrate is an excellent experimental platform to study the interplay between superfluid and structural orders. Here, we report a rigid two-frequency torsional oscillator study on the second layer as a function of temperature and ${}^4\mathrm{He}$ atomic density. For the first time, we show experimentally that the superfluid density is independent of frequency, which can be interpreted as unequivocal evidence of genuine superfluidity. The phase diagram established in this work reveals that a superfluid phase coexists with hexatic density-wave correlation and a registered solid phase. This suggests the second layer as a candidate for hosting two exotic quantum ground states: the spatially modulated superfluid and supersolid phases resulting from the interplay between superfluid and structural orders.