Searches for the axion and axionlike particles may hold the key to unlocking some of the deepest puzzles about our Universe, such as dark matter and dark energy. Here, we use the recently demonstrated spin-based amplifier to constrain such hypothetical particles within the well-motivated “axion window” ($10\mu \mathrm{eV}–1\mathrm{meV}$) through searching for an exotic dipole-dipole interaction between polarized electron and neutron spins. The key ingredient is the use of hyperpolarized long-lived ${}^{129}\mathrm{Xe}$ nuclear spins as an amplifier for the pseudomagnetic field generated by the exotic interaction. Using such a spin sensor, we obtain a direct upper bound on the product of coupling constants $g_p^e{g}_p^n$. The spin-based amplifier technique can be extended to searches for a wide variety of hypothetical particles beyond the standard model.

Symbolic regression identifies nonlinear, analytical expressions relating materials properties and key physical parameters. However, the pool of expressions grows rapidly with complexity, compromising its efficiency. We tackle this challenge hierarchically: identified expressions are used as inputs for further obtaining more complex expressions. Crucially, this framework can transfer knowledge among properties, as demonstrated using the sure-independence-screening-and-sparsifying-operator approach to identify expressions for lattice constant and cohesive energy, which are then used to model the bulk modulus of $AB{\mathrm{O}}_3$ perovskites.

Intermediate-scale quantum technologies provide new opportunities for scientific discovery, yet they also pose the challenge of identifying suitable problems that can take advantage of such devices in spite of their present-day limitations. In solid-state materials, fractional quantum Hall phases continue to attract attention as hosts of emergent geometrical excitations analogous to gravitons, resulting from the nonperturbative interactions between the electrons. However, the direct observation of such excitations remains a challenge. Here, we identify a quasi-one-dimensional model that captures the geometric properties and graviton dynamics of fractional quantum Hall states. We then simulate geometric quench and the subsequent graviton dynamics on the IBM quantum computer using an optimally compiled Trotter circuit with bespoke error mitigation. Moreover, we develop an efficient, optimal-control-based variational quantum algorithm that can efficiently simulate graviton dynamics in larger systems. Our results open a new avenue for studying the emergence of gravitons in a new class of tractable models on the existing quantum hardware.

The excitonic fine structure plays a key role for the quantum light generated by semiconductor quantum dots, both for entangled photon pairs and single photons. Controlling the excitonic fine structure has been demonstrated using electric, magnetic, or strain fields, but not for quantum dots in optical cavities, a key requirement to obtain high source efficiency and near-unity photon indistinguishability. Here, we demonstrate the control of the fine structure splitting for quantum dots embedded in micropillar cavities. We propose and implement a scheme based on remote electrical contacts connected to the pillar cavity through narrow ridges. Numerical simulations show that such a geometry allows for a three-dimensional control of the electrical field. We experimentally demonstrate tuning and reproducible canceling of the fine structure, a crucial step for the reproducibility of quantum light source technology.

We experimentally realized a time-periodically modulated 1D lattice for ultracold atoms featuring a pair of linear bands, each with a Floquet winding number. These bands are spin-momentum locked and almost perfectly linear everywhere in the Brillouin zone: a near-ideal realization of the 1D Dirac Hamiltonian. We characterized the Floquet winding number using a form of quantum state tomography, covering the Brillouin zone and following the micromotion through one Floquet period. Last, we altered the modulation timing to lift the topological protection, opening a gap at the Dirac point that grew in proportion to the deviation from the topological configuration.

Angular oscillations can provide a useful probe of the superfluid properties of a system. Such measurements have recently been applied to dipolar supersolids, which exhibit both density modulation and phase coherence, and for which robust probes of superfluidity are particularly interesting. So far, these investigations have been confined to linear droplet arrays, which feature relatively simple excitation spectra, but limited sensitivity to the effects of superfluidity. Here, we explore angular oscillations in systems with 2D structure which, in principle, have greater sensitivity to superfluidity. In both experiment and simulation, we find that the interplay of superfluid and crystalline excitations leads to a frequency of angular oscillations that remains nearly unchanged even when the superfluidity of the system is altered dramatically. This indicates that angular oscillation measurements do not always provide a robust experimental probe of superfluidity with typical experimental protocols.

Unwanted $ZZ$ interaction is a quantum-mechanical crosstalk phenomenon which correlates qubit dynamics and is ubiquitous in superconducting qubit systems. It adversely affects the quality of quantum operations and can be detrimental in scalable quantum information processing. Here we propose and experimentally demonstrate a practically extensible approach for complete cancellation of residual $ZZ$ interaction between fixed-frequency transmon qubits, which are known for long coherence and simple control. We apply to the intermediate coupler that connects the qubits a weak microwave drive at a properly chosen frequency in order to noninvasively induce an ac Stark shift for $ZZ$ cancellation. We verify the cancellation performance by measuring vanishing two-qubit entangling phases and $ZZ$ correlations. In addition, we implement a randomized benchmarking experiment to extract the idling gate fidelity which shows good agreement with the coherence limit, demonstrating the effectiveness of $ZZ$ cancellation. Our method allows independent addressability of each qubit-qubit connection and is applicable to both nontunable and tunable couplers, promising better compatibility with future large-scale quantum processors.

In periodic systems, nodal lines are loops in the three-dimensional momentum space with each point on them representing a band degeneracy. Nodal lines exhibit rich topological features, as they can take various configurations such as rings, links, chains, and knots. These line nodes are generally protected by mirror or $PT$ symmetry and frequently accompanied by drumhead surface states. Here, we propose and demonstrate a novel type of photonic straight nodal lines in a ${\mathrm{D}}_{2\mathrm{D}}$ metacrystal, which are protected by an unusual rotoinversion time (roto-$PT$) symmetry. These nodal lines are located at the central axis and hinges of the Brillouin zone. They appear as quadrupole sources of Berry curvature flux in contrast to the Weyl points, which are monopoles. Interestingly, topological surface states exist at all three cutting surfaces, as guaranteed by $\pi$-quantized Zak phases along all three directions. As frequency changes, the surface state equifrequency contours evolve from closed to open and become straight lines at a critical transition frequency, at which diffractionless surface wave propagations are experimentally demonstrated, paving the way toward development of superimaging topological devices.

Ferroelasticity is a prominent material property analogous to ferroelectricity and ferromagnetism, but its characteristic spontaneous structural polarization has remained less studied and poorly understood. Here, we use a high-throughput computation approach in conjunction with first-principles calculations to identify 65 ($M=\text{transition}$ metal, $X=\text{nonmetal}$) monolayers exhibiting in-plane ferroelasticity out of 166 stable tetragonal monolayers. Molecular orbital theory analysis reveals that ferroelastic distortion arises when $M\text{−}d/X\text{−}p$ and $M\text{−}d/M\text{−}d$ couplings are both sufficiently weak. We have developed a physically interpretable one-dimensional descriptor that correctly predicts 89% of ferroelastics or nonferroelastics among the examined MX monolayers. Moreover, we find eleven $MX$ compounds that exhibit strongly coupled ferroelasticity and magnetism driven by strain-controlled magnetocrystalline anisotropy, raising the prospects of developing 2D ferroelasticity-based multiferroics.

We present a covariant continuum formulation of a generalized two-dimensional vertexlike model of epithelial tissues which describes tissues with different underlying geometries, and allows for an analytical macroscopic description. Using a geometrical approach and out-of-equilibrium statistical mechanics, we calculate both mechanical and dynamical instabilities of a tissue, and their dependences on various variables, including activity, and cell-shape heterogeneity (disorder). We show how both plastic cellular rearrangements and the tissue elastic response depend on the existence of mechanical residual stresses at the cellular level. Even freely growing tissues may exhibit a growth instability depending on the intrinsic proliferation rate. Our main result is an explicit calculation of the cell pressure in a homeostatic state of a confined growing tissue. We show that the homeostatic pressure can be negative and depends on the existence of mechanical residual stresses. This geometric model allows us to sort out elastic and plastic effects in a growing, flowing, tissue.

We investigate the emergence of complex dynamics in networks with heavy-tailed connectivity by developing a non-Hermitian random matrix theory. We uncover the existence of an extended critical regime of spatially multifractal fluctuations between the quiescent and active phases. This multifractal critical phase combines features of localization and delocalization and differs from the edge of chaos in classical networks by the appearance of universal hallmarks of Anderson criticality over an extended region in phase space. We show that the rich nonlinear response properties of the extended critical regime can account for a variety of neural dynamics such as the diversity of timescales, providing a computational advantage for persistent classification in a reservoir setting.

The segregation of solute atoms at grain boundaries (GBs) can strongly impact the structural and functional properties of polycrystals. Yet, due to the limited availability of simulation tools to study polycrystals at the atomistic scale (i.e., interatomic potentials), there is a minimal understanding of the variation of solute segregation tendencies across the very complex space of GB microenvironments and the large range of alloys in which it can occur. Here, we develop an algorithmic framework that can directly learn the full spectrum of segregation energies for a metal solute atom in a metal polycrystal from ab initio methods, bypassing the need for alloy interatomic potentials. This framework offers a pathway to a comprehensive catalog of GB solute segregation with quantum accuracy, for the entire alloy space. As an initial demonstration in this pursuit, we build an extensive GB segregation database for aluminum-based alloys across the periodic table, including dozens of alloys for which there are substantially no prior data.

Gravitational waves (GWs) generate oscillating electromagnetic effects in the vicinity of external electric and magnetic fields. We discuss this phenomenon with a particular focus on reinterpreting the results of axion haloscopes based on lumped-element detectors, which probe GWs in the 100 kHz–100 MHz range. Measurements from ABRACADABRA and SHAFT already place bounds on GWs, although the present strain sensitivity is weak. However, we demonstrate that the sensitivity scaling with the volume of such instruments is significant—faster than for axions—and so rapid progress will be made in the future. With no modifications, DMRadio-${\mathrm{m}}^3$ will have a GW strain sensitivity of $h\sim {10}^{-20}$ at 200 MHz. A simple modification of the pickup loop used to readout the induced magnetic flux can parametrically enhance the GW sensitivity, particularly at lower frequencies.