We describe and benchmark a new quantum charge-coupled device (QCCD) trapped-ion quantum computer based on a linear trap with periodic boundary conditions, which resembles a race track. The new system successfully incorporates several technologies crucial to future scalability—including electrode broadcasting, multilayer rf routing, and magneto-optical trap (MOT) loading—while maintaining, and in some cases exceeding, the gate fidelities of previous QCCD systems. The system is initially operated with 32 qubits, but future upgrades will allow for more. We benchmark the performance of primitive operations, including an average state preparation and measurement error of $1.6(1)\times {10}^{-3}$, an average single-qubit gate infidelity of $2.5(3)\times {10}^{-5}$, and an average two-qubit gate infidelity of $1.84(5)\times {10}^{-3}$. The system-level performance of the quantum processor is assessed with mirror benchmarking, linear cross-entropy benchmarking, a quantum volume measurement of $\mathrm{QV}=2^{16}$, and the creation of 32-qubit entanglement in a GHZ state. We also tested application benchmarks, including Hamiltonian simulation, QAOA, error correction on a repetition code, and dynamics simulations using qubit reuse. We also discuss future upgrades to the new system aimed at adding more qubits and capabilities.

The effort to discover a quantum theory of gravity is motivated by the need to reconcile the incompatibility between quantum theory and general relativity. Here, we present an alternative approach by constructing a consistent theory of classical gravity coupled to quantum field theory. The dynamics is linear in the density matrix, completely positive, and trace preserving, and reduces to Einstein’s theory of general relativity in the classical limit. Consequently, the dynamics does not suffer from the pathologies of the semiclassical theory based on expectation values. The assumption that general relativity is classical necessarily modifies the dynamical laws of quantum mechanics; the theory must be fundamentally stochastic in both the metric degrees of freedom and in the quantum matter fields. This breakdown in predictability allows it to evade several no-go theorems purporting to forbid classical quantum interactions. The measurement postulate of quantum mechanics is not needed; the interaction of the quantum degrees of freedom with classical space-time necessarily causes decoherence in the quantum system. We first derive the general form of classical quantum dynamics and consider realizations which have as its limit deterministic classical Hamiltonian evolution. The formalism is then applied to quantum field theory interacting with the classical space-time metric. One can view the classical quantum theory as fundamental or as an effective theory useful for computing the backreaction of quantum fields on geometry. We discuss a number of open questions from the perspective of both viewpoints.

Understanding the materials dependence together with the universal controlling parameter of superconductivity (SC) in copper oxide superconductors is one of the major challenges in condensed matter physics. Here, we numerically analyze SC by using ab initio low-energy effective Hamiltonians consisting of the antibonding combination of Cu $3d_{x^2-y^2}$ and O $2p_{\sigma }$ orbitals without adjustable parameters. We have performed the state-of-the-art variational Monte Carlo calculations for the four carrier doped cuprates with diverse experimental optimal SC critical temperature $T_c^{\mathrm{opt}}$: ${\mathrm{CaCuO}}_2$ ($T_c^{\mathrm{opt}}\sim 110\mathrm{K}$), ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CuO}}_6$ ($T_c^{\mathrm{opt}}\sim 10–40\mathrm{K}$), ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_8$ ($T_c^{\mathrm{opt}}\sim 85–100\mathrm{K}$), and ${\mathrm{HgBa}}_2{\mathrm{CuO}}_4$ ($T_c^{\mathrm{opt}}\sim 90\mathrm{K}$). Materials and hole doping concentration ($\delta$) dependencies of the SC order parameter $F_{\mathrm{SC}}$ and the competition with spin or charge order show essential and quantitative agreement with the available experiments on the four materials in the following points. (1) In a wide range $0.05\le \delta \le 0.25$, the ground state is commonly the uniform SC state, which is severely competing with the charge or spin stripe and antiferromagnetic states. (2) $F_{\mathrm{SC}}$ at the optimum doping shows amplitude consistent with the superfluid density measured in the muon spin resonance and its dome structure found in $\delta$ dependence shows consistency with that of the SC gap in the tunneling and photoemission measurements. Based on the confirmed materials dependence, we further find insights into the universal SC mechanism. (I) $F_{\mathrm{SC}}$ increases with the ratio $U/|t_1|$ within the available realistic materials, indicating that $U/|t_1|$ is the principal component controlling the strength of the SC in the real materials dependence. Here, $U$ and $t_1$ are the on-site Coulomb repulsion and the nearest neighbor hopping, respectively, in the ab initio Hamiltonians. (II) A universal scaling $T_c^{\mathrm{opt}}\sim 0.16|t_1|F_{\mathrm{SC}}$ holds. (III) SC is enhanced and optimized if $U$ is increased beyond the real available materials, and it is further enhanced when the off-site interaction is reduced, while the presence of the off-site interaction is important to make the SC ground state against other competing states. The present findings provide useful clues for the design of new SC materials with even higher $T_c^{\mathrm{opt}}$.

Midcircuit operations, such as qubit state measurement or reset, are central to many tasks in quantum information science, including quantum computing, entanglement generation, and metrology. For instance, in quantum error correction, the information gained from a measurement on a subset of qubits is used to influence the state of the remaining unmeasured qubits, rectifying inevitable errors that arise in a quantum circuit. Such partial projective operations pose a challenge for dense neutral atom arrays and trapped ions, where accidental exposure to resonant laser light during quantum state initialization and detection can spoil the state of untargeted qubits. In this work, we implement midcircuit operations in a 48-site array of neutral atoms, enabled by new methods for high-fidelity control of the omg (optical-metastable-ground-state qubit) architecture present in ${}^{171}\mathrm{Yb}$. Here, the quantum information is encoded in either of the three qubit manifolds and can be shuttled between them. With state-sensitive shelving between the ground and metastable states, we realize a nondestructive state detection for ${}^{171}\mathrm{Yb}$, incorporating global control and local feed-forward operations. Using new schemes for local addressing of the optical clock transition, we shelve a subset of qubits to the metastable state, hiding them from projective operations performed on the qubits remaining in the ground state, demonstrating midcircuit measurement, spin reset, and motional reset in the form of ground-state cooling.

Measurement-based quantum error correction relies on the ability to determine the state of a subset of qubits (ancillas) within a processor without revealing or disturbing the state of the remaining qubits. Among neutral-atom-based platforms, a scalable, high-fidelity approach to midcircuit measurement that retains the ancilla qubits in a state suitable for future operations has not yet been demonstrated. In this work, we perform maging using a narrow-linewidth transition in an array of tweezer-confined ${}^{171}\mathrm{Yb}$ atoms to demonstrate nondestructive state-selective and site-selective detection. By applying site-specific light shifts, selected atoms within the array can be hidden from imaging light, which allows a subset of qubits to be measured while causing only percent-level errors on the remaining qubits. As a proof-of-principle demonstration of conditional operations based on the results of the midcircuit measurements, and of our ability to reuse ancilla qubits, we perform conditional refilling of ancilla sites to correct for occasional atom loss, while maintaining the coherence of data qubits. Looking toward true continuous operation, we demonstrate loading of a magneto-optical trap with a minimal degree of qubit decoherence.

Metamaterials, from optics to radio frequencies and acoustics, have attracted significant attention over the last few decades, with promising applications in a wide range of technological areas. However, it has been recognized that their performance is often hindered by ubiquitous material loss and nonlocal phenomena. A canonical problem consists in imaging through metamaterial superlenses, which hold the promise of superresolution but which are, in practice, limited by material loss as we attempt to image deeply subwavelength details. Active metamaterials have been explored to compensate for loss; however, material gain introduces other obstacles, e.g., instabilities, nonlinearity, and noise. Here, we demonstrate that the temporal excitation of passive metamaterials using signals oscillating at complex frequencies can effectively compensate material loss, leading to resolution enhancement when applied to metamaterial superlenses. More broadly, our results demonstrate that virtual gain stemming from tailored forms of excitation can tackle the impact of loss in metamaterials, opening promising avenues for a broad range of applications from acoustic to photonic technologies.

Quantum noise imposes a fundamental limitation on the sensitivity of interferometric gravitational-wave detectors like LIGO, manifesting as shot noise and quantum radiation pressure noise. Here, we present the first realization of frequency-dependent squeezing in full-scale gravitational-wave detectors, resulting in the reduction of both shot noise and quantum radiation pressure noise, with broadband detector enhancement from tens of hertz to several kilohertz. In the LIGO Hanford detector, squeezing reduced the detector noise amplitude by a factor of 1.6 (4.0 dB) near 1 kHz; in the Livingston detector, the noise reduction was a factor of 1.9 (5.8 dB). These improvements directly impact LIGO’s scientific output for high-frequency sources (e.g., binary neutron star postmerger physics). The improved low-frequency sensitivity, which boosted the detector range by 15%–18% with respect to no squeezing, corresponds to an increase in the astrophysical detection rate of up to 65%. Frequency-dependent squeezing was enabled by the addition of a 300-meter-long filter cavity to each detector as part of the LIGO $\mathrm{A}+$ upgrade.

Electronic Fabry-Pérot interferometry is a powerful method to probe quasiparticle charge and anyonic braiding statistics in the fractional quantum Hall regime. We extend this technique to the hierarchy $\nu =2/5$ fractional quantum Hall state, possessing two edge modes that in our device can be interfered independently. The outer edge mode exhibits interference similar to the behavior observed at the $\nu =1/3$ state, indicating that the outer edge mode at $\nu =2/5$ has properties similar to the single mode at $\nu =1/3$. The inner mode shows an oscillation pattern with a series of discrete phase jumps indicative of distinct anyonic braiding statistics. After taking into account the impact of bulk-edge coupling, we extract an interfering quasiparticle charge $e^{*}=0.17\pm 0.02$ and anyonic braiding phase ${\theta }_a=(-0.43\pm 0.05)\times 2\pi$, which serve as experimental verification of the theoretically predicted values of $e^{*}=\frac{1}{5}$ and ${\theta }_a=-(4\pi /5)$.

Turing proposed a reaction-diffusion (RD) process as the chemical basis of morphogenesis. Despite the elegance of this model, its relevance for the precise description of morphogenesis in real organisms is largely disputed. Here, we show that a simple RD system, predicting the cellular-automaton-like patterning of ocellated lizards’ skin into green and black labyrinthine chains of scales, additionally predicts unsuspected subtle color subclustering that correlates with the colors of the scales’ neighbors. Hyperspectral imaging indicates that color subclustering is present in real lizards, confirming the numerical model nontrivial prediction. In addition, extensive histological analyses show that melanophores’ spatial distribution correlates with scale neighborhood, confirming that color subclustering is associated to the underlying microscopic system of chromatophore interactions. We then show that the observed subclustering is efficiently captured by RD models, irrespective of their form, discretization, and spatial dimensionality. We also show that sets of values can be identified in the 12-dimensional RD parameter space to yield the correct direction of correlation (i.e., observed in real lizards) between green-scale blackness and their neighborhood configuration, hence instructing the mathematical model. More generally, our results show that subtle mesoscopic properties of biological dynamical systems, as well as some of the underlying microscopic features, are quantitatively captured by simple RD models without integrating the unmanageable profusion of variables at lower scales.

Thermodynamically induced length fluctuations of high-reflectivity mirror coatings put a fundamental limit on sensitivity and stability of precision optical interferometers like gravitational-wave detectors and ultrastable lasers. The main contribution—Brownian thermal noise—is related to the mechanical loss of the coating material. ${\mathrm{Al}}_{0.92}{\mathrm{Ga}}_{0.08}\mathrm{As}/\mathrm{GaAs}$ crystalline mirror coatings are expected to reduce this limit. The first measurements of cryogenic silicon cavities revealed the existence of additional noise contributions exceeding the expected Brownian thermal noise. We describe a novel, nonthermal, photoinduced effect in birefringence that is most likely related to the recently discovered birefringence noise. Our studies of the dynamics and power dependence are an important step toward uncovering the underlying mechanisms. Averaging the anticorrelated birefringent noise results in a residual noise that is shown to be substantially different from Brownian thermal noise. To this end, we develop a new method for analyzing the coating noise in higher-order transverse-cavity modes, which makes it possible for the first time to determine the contribution of Brownian thermal noise to the total cavity noise. The new noise contributions must be considered carefully in precision interferometry experiments using similar coatings based on semiconductor materials.

The interplay between strong correlations and topology can lead to the emergence of intriguing quantum states of matter. One well-known example is the fractional quantum Hall effect, where exotic electron fluids with fractionally charged excitations form in partially filled Landau levels. The emergence of topological moiré flat bands provides exciting opportunities to realize the lattice analogs of both the integer and fractional quantum Hall effects without the need for an external magnetic field. These effects are known as the integer and fractional quantum anomalous Hall (IQAH and FQAH) effects. Here, we present direct transport evidence of the existence of both IQAH and FQAH effects in small-angle-twisted bilayer ${\mathrm{MoTe}}_2$. At zero magnetic field, we observe well-quantized Hall resistance of $h/e^2$ around moiré filling factor $\nu =-1$ (corresponding to one hole per moiré unit cell), and nearly quantized Hall resistance of $3h/2e^2$ around $\nu =-2/3$, respectively. Concomitantly, the longitudinal resistance exhibits distinct minima around $\nu =-1$ and $-2/3$. The application of an electric field induces topological quantum phase transition from the IQAH state to a charge transfer insulator at $\nu =-1$, and from the FQAH state to a topologically trivial correlated insulator, further transitioning to a metallic state at $\nu =-2/3$. Our study paves the way for the investigation of fractionally charged excitations and anyonic statistics at zero magnetic field based on semiconductor moiré materials.

The interaction between a mobile quantum impurity and a bosonic bath leads to the formation of quasiparticles, termed Bose polarons. The elementary properties of Bose polarons, such as their mutual interactions, can differ drastically from those of the bare impurities. Here, we explore Bose polaron physics in a two-dimensional nonequilibrium setting by injecting ${\sigma }^{-}$ polarized exciton-polariton impurities into a bath of coherent ${\sigma }^{+}$ polarized polaritons generated by resonant laser excitation of monolayer ${\mathrm{MoSe}}_2$ embedded in an optical cavity. By exploiting a biexciton Feshbach resonance between the impurity and the bath polaritons, we tune the interacting system to the strong-coupling regime and demonstrate the coexistence of two new quasiparticle branches. Using time-resolved pump-probe measurements, we observe how polaron dressing modifies the interaction between impurity polaritons. Remarkably, we find that the interactions between high-energy polaron quasiparticles, which are repulsive for small bath occupancy, can become attractive in the strong impurity-bath coupling regime. Our experiments provide the first direct measurement of Bose polaron-polaron interaction strength in any physical system and pave the way for exploration and control of many-body correlations in driven-dissipative settings.

A short superconducting segment can couple attached quantum dots via elastic cotunneling (ECT) and crossed Andreev reflection (CAR). Such coupled quantum dots can host Majorana bound states provided that the ratio between CAR and ECT can be controlled. Metallic superconductors have so far been shown to mediate such tunneling phenomena, albeit with limited tunability. Here, we show that Andreev bound states formed in semiconductor-superconductor heterostructures can mediate CAR and ECT over mesoscopic length scales. Andreev bound states possess both an electron and a hole component, giving rise to an intricate interference phenomenon that allows us to tune the ratio between CAR and ECT deterministically. We further show that the combination of intrinsic spin-orbit coupling in InSb nanowires and an applied magnetic field provides another efficient knob to tune the ratio between ECT and CAR and optimize the amount of coupling between neighboring quantum dots.

The kagome superconductor family $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ ($A=\mathrm{Cs}$, K, Rb) emerged as an exciting platform to study exotic Fermi surface instabilities. Here, we use spectroscopic-imaging scanning tunneling microscopy (SI-STM) and angle-resolved photoemission spectroscopy (ARPES) to reveal how the surprising cascade of higher- and lower-dimensional density waves in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ is intimately tied to a set of small reconstructed Fermi pockets. ARPES measurements visualize the formation of these pockets generated by a 3D charge density wave transition. The pockets are connected by dispersive $q^{*}$ wave vectors observed in Fourier transforms of STM differential conductance maps. As the additional 1D charge order emerges at a lower temperature, $q^{*}$ wave vectors become substantially renormalized, signaling further reconstruction of the Fermi pockets. Remarkably, in the superconducting state, the superconducting gap modulations give rise to an in-plane Cooper pair density wave at the same $q^{*}$ wave vectors. Our work demonstrates the intrinsic origin of the charge stripes and the pair density wave in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ and their relationship to the Fermi pockets. These experiments uncover a unique scenario of how Fermi pockets generated by a parent charge density wave state can provide a favorable platform for the emergence of additional density waves.

Most animal brains present two mirror-symmetric sides, but closer inspection reveals a range of asymmetries (in shape and function) that seem more salient in more cognitively complex species. Sustaining symmetric, redundant neural circuitry has associated metabolic costs, but it might aid in implementing computations within noisy environments or with faulty pieces. It has been suggested that the complexity of a computational task might play a role in breaking bilaterally symmetric circuits into fully lateralized ones; however, a rigorous, mathematically grounded theory of how this mechanism might work is missing. Here, we provide such a mathematical framework, starting with the simplest assumptions but extending our results to a comprehensive range of biologically relevant scenarios. We show mathematically that only fully lateralized or bilateral solutions are relevant within our framework (dismissing configurations in which circuits are only partially engaged). We provide maps that show when each configuration is preferred depending on costs, fitness contributed, circuit reliability, and task complexity. We discuss evolutionary paths leading from bilateral to lateralized configurations and other possible outcomes. The implications of these results for evolution, development, and rehabilitation of damaged or aging brains is discussed. Our work constitutes a limit case that should constrain and underlie similar mappings when other aspects (besides task complexity and circuit reliability) are considered.

In this work, we lay down the ab initio many-body quantum theory of electrons and phonons in equilibrium as well as in steady-state or time-varying settings. Our focus is on the harmonic approximation, but the developed tools can readily incorporate anharmonic effects. We begin by showing the necessity of determining the ab initio Hamiltonian in a self-consistent manner to ensure the existence of an equilibrium state. We then identify the correct partitioning into a “noninteracting” and an “interacting” part to carry out diagrammatic expansions in terms of dressed propagators and screened interactions. The final outcome is the finite-temperature nonequilibrium extension of the Hedin equations, showcasing the emergence of the coupling between electrons and coherent phonons through the time-local Ehrenfest diagram. The Hedin equations have limited practical utility for real-time simulations of systems driven out of equilibrium by external fields. To overcome this limitation, we leverage the versatility of the diagrammatic approach to generate a closed system of differential equations for the dressed propagators and nuclear displacements. These are the Kadanoff-Baym equations for electrons and phonons. The formalism naturally merges with the theory of conserving approximations, which guarantee the satisfaction of the continuity equation and the conservation of total energy during time evolution. As an example, we show that the popular Born-Oppenheimer approximation is not conserving whereas its dynamical extension is conserving, provided that the electrons are treated in the Fan-Migdal approximation with a dynamically screened electron-phonon coupling. We also derive the formal solution of the Kadanoff-Baym equations for nonequilibrium steady states, which is useful for studies in photovoltaics and optoelectronics. Interestingly, the expansion of the phononic Green’s function around the quasiphonon energies points to a correlation-induced splitting of the phonon dispersion in materials with no time-reversal invariance.

Pathological morphological changes in tumor tissue enable collective cancer cell unjamming, a cellular motility transition. However, fundamental questions remain: Is unjamming essential for tumor progression? Which different unjamming states can be found in patients? Here, vital cell tracking in patient-derived solid tumor explants ($N=16$) reveals that states of cell unjamming can be recognized by elongated cell and nucleus shape (CeNuS) and low nucleus number density. These static variables serve as a morphodynamic link to map the broad range of morphologies and associated motility states found in histological slides of 1380 breast cancer patients to generate a comprehensive state diagram of cancer cell unjamming. An increase in predicted cell motility in primary tumors through unjamming significantly correlates with distant metastases that may even occur a decade later. Patient risk groups are quantified via a decision boundary in the state space found by machine learning. The resulting clinical prognostic potential is evaluated using a range of quantifiers, including Harrel’s concordance index. Using multivariable Cox models, we find that cell unjamming as a prognostic parameter adds a 26% information gain in the concordance index when combined with the established prognostic criteria (tumor diameter, tumor grade, lymph node status) used in the Nottingham index. Unjamming complements the information on affected lymph nodes in patients regarding metastatic risk. The derived state diagram of cancer cell unjamming reconciles conflicting observations regarding shape- or density-induced unjamming and stresses the nuclei’s mechanical importance, which is not considered in current theories of cell unjamming. We conclude that cancer cell unjamming is part of the metastatic cascade; thus, an emergent physical phenomenon contributes to tumor progression.

We demonstrate a superconducting artificial atom with strong unidirectional coupling to a microwave photonic waveguide. Our artificial atom is realized by coupling a transmon qubit to the waveguide at two spatially separated points with time-modulated interactions. Direction-sensitive interference arising from the parametric couplings in our scheme results in a nonreciprocal response, where we measure a forward/backward ratio of spontaneous emission exceeding 100. We verify the quantum nonlinear behavior of this artificial chiral atom by measuring the resonance fluorescence spectrum under a strong resonant drive and observing well-resolved Mollow triplets. Further, we demonstrate chirality for the second transition energy of the artificial atom and control it with a pulse sequence to realize a qubit-state-dependent nonreciprocal phase on itinerant photons. Our demonstration puts forth a superconducting hardware platform for the scalable realization of several key functionalities pursued within the paradigm of chiral quantum optics, including quantum networks with all-to-all connectivity, driven-dissipative stabilization of many-body entanglement, and the generation of complex nonclassical states of light.

Gravitational-wave observations of extreme mass ratio inspirals (EMRIs) offer the opportunity to probe the environments of active galactic nuclei (AGN) through the torques that accretion disks induce on the binary. Within a Bayesian framework, we study how well such environmental effects can be measured using gravitational wave observations from the Laser Interferometer Space Antenna (LISA). We focus on the torque induced by planetary-type migration on quasicircular inspirals and use different prescriptions for geometrically thin and radiatively efficient disks. We find that LISA could detect migration for a wide range of disk viscosities and accretion rates, for both $\alpha$ and $\beta$ disk prescriptions. For a typical EMRI with masses $50M_{\odot }+{10}^6{M}_{\odot }$, we find that LISA could distinguish between migration in $\alpha$ and $\beta$ disks and measure the torque amplitude with $\sim 20\%$ relative precision. Provided an accurate torque model, we also show how to turn gravitational-wave measurements of the torque into constraints on the disk properties. Furthermore, we show that, if an electromagnetic counterpart is identified, the multimessenger observations of the AGN EMRI system will yield direct measurements of the disk viscosity. Finally, we investigate the impact of neglecting environmental effects in the analysis of the gravitational-wave signal, finding $3\sigma$ biases in the primary mass and spin, and showing that ignoring such effects can lead to false detection of a deviation from general relativity. This work demonstrates the scientific potential of gravitational observations as probes of accretion-disk physics, accessible so far through electromagnetic observations only.

In 1935, Einstein, Podolsky, and Rosen (EPR) conceived a gedanken experiment which became a cornerstone of quantum technology and still challenges our understanding of reality and locality today. While the experiment has been realized with small quantum systems, a demonstration of the EPR paradox with massive many-particle systems remains an important challenge, as such systems are particularly closely tied to the concept of local realism in our everyday experience and may serve as probes for new physics at the quantum-to-classical transition. In this work we report an EPR experiment with two spatially separated Bose-Einstein condensates, each containing about 700 rubidium atoms. Entanglement between the condensates results in strong correlations of their collective spins, allowing us to demonstrate the EPR paradox between them. Our results represent the first observation of the EPR paradox with spatially separated, massive many-particle systems. They show that the conflict between quantum mechanics and local realism does not disappear as the system size increases to more than a thousand massive particles. Furthermore, EPR entanglement in conjunction with individual manipulation of the two condensates on the quantum level, as we demonstrate here, constitutes an important resource for quantum metrology and information processing with many-particle systems.