Neutron-rich boron isotopes provide a valuable testing ground for threshold-driven structure and reaction phenomena, including halo formation and exotic decay modes. In particular, the structure of ${}^{17}\mathrm{B}$ and its relation to unbound ${}^{16}\mathrm{B}$ are of special interest. The ${}^{16}\mathrm{B}$ nucleus is slightly unbound by approximately 50 keV, while ${}^{17}\mathrm{B}$ is bound with a neutron separation energy of about 1.4–1.6 MeV. The observation of a 1640 keV $\gamma$ ray in ${}^{17}\mathrm{B}$, which we argue originates from a $1/2^{-}$ excited state, points to a remarkable situation in which $\gamma$ decay and two-neutron decay can compete. We analyze and identify the main reasons for the competition: $L=2$ emission of the neutron pair and structural realignment driven by the proximity of the one-body threshold, in particular the nearby $s$-wave neutron decay channel. The decay is a unique near-threshold $L=2$ process in which multiple structural components contribute, each with coexisting direct and virtual sequential amplitudes whose interference governs the observables. Because threshold dynamics, continuum coupling, and interference of multiple quantum pathways are universal, closely related scenarios arise in ultracold atoms near Feshbach resonances, few-body atomic and molecular breakups, mesoscopic and photonic open systems, and other areas where open-quantum-system effects impact observables. We employ advanced theoretical models to study this first-of-its-kind case and provide a coherent theoretical perspective based on configuration interaction and complex-energy formalisms that incorporate both reaction continuum and structural effects near threshold.

Quantum magic, which accounts for the nonstabilizer content of a state, is essential for universal quantum computation beyond classically simulable resources. However, the way magic builds up during structured unitary dynamics remains largely open. Here, we investigate the generation and evolution of quantum magic in discrete-time quantum walks (DTQWs)—a simple, tunable unitary model realizable on a wide range of architectures. We use stabilizer Rényi entropy as a measure of quantum magic and investigate single- and two-walker quantum walks on a one-dimensional lattice, considering a wide range of initial coin states. Our results reveal that DTQWs can dynamically generate significant magic, with the amount and structure dependent on the initial state of the coin. In the case of a single walker, we found a nontrivial and complementary relationship between magic and entanglement at long times. In the two-walker setting, even states close to stabilizer form can evolve into highly magical states when subjected to quantum walk protocols. The generation of magic can occur independently of entanglement growth, emphasizing its distinct role as a quantum resource. We further show that the dynamical magic generation is robust under realistic noise—specifically, decoherence in the coin degree of freedom—demonstrating that this process persists across noisy settings. Finally, we discuss an experimentally feasible scheme to measure magic using current technology. Our findings position DTQWs as accessible and controllable platforms for producing quantum magic, offering a fresh perspective on their role in quantum information processing and reliable quantum computation.

Building on the standard hierarchy of pure states (HOPS) approach, we construct a generalized formulation suitable for open quantum systems interacting with nonstationary Gaussian baths, potentially extending its applicability to nonequilibrium baths. This is achieved by extending the conventional exponential decomposition of a bath-correlation function (BCF) for nonstationary cases. Using our formulation of HOPS, we derive the corresponding hierarchy of master equations and, when each term in the BCF expansion can be associated with an independent physical bath, we show how the formalism connects to the well-known pseudomode representation. We demonstrate the method's performance on two examples of nonstationary squeezed reservoirs generated via uniform squeezing and degenerate parametric amplification in a one-sided cavity. Benchmarking against the hierarchy of master equations shows that HOPS is more efficient under hierarchy truncation. The pseudomode representation is shown to be more efficient in the strongly non-Markovian regime. Our results highlight HOPS as a versatile and powerful tool for simulating open quantum systems in nonstationary baths, with potential applications ranging from squeezed light-matter interactions to driven-quantum materials and dissipative phase transitions.

Optical interference usually requires two interfering paths to be balanced within the coherence length. For the case of unbalanced paths, interference effects can be recovered in the frequency-domain analysis of the superposed resultant optical field because optical frequency filtering in the spectral analysis of the optical field lengthens the coherence length to overcome the path imbalance. However, since optical detection usually is intensity measurement that loses the phase information of the detected optical field, the output photocurrent of intensity measurement cannot recover the lost interference effect in the postprocessing of the data such as electronic spectral analysis. On the other hand, if amplitude measurement can be used to measure the resultant optical field from the path-unbalanced superposition of two fields, the output photocurrent carries complete information of two fields and can restore interference in postdetection processing, even though no interference shows up in direct intensity measurement. In this paper, we use homodyne detection method for amplitude measurement to analyze the output of a path-unbalanced interferometer in the spectral domain. Since complete information about the superposed optical field is contained in the photocurrent, spectral analysis shows interference fringes in frequency that reveal information about the path imbalance. It is found that shot noise is the limiting factor in the visibility of interference but can be reduced with a squeezed state input in the unused port of the unbalanced interferometer. This approach is a different paradigm from the traditional one for studying the coherence between optical fields and should find wide application in remote sensing and precision measurement.

Quantum nonlocality in networks featuring multiple independent sources underpins large-scale quantum communication and poses fundamental challenges for its characterization. In this work, we construct a family of explicit nonlinear Bell inequalities to verify the nonlocality across the general multi-input quantum networks. The construction of these inequalities relies on the number of leaf nodes, a network parameter that can be identified by a linear-time algorithm. Our approach establishes a structural connection between bipartite full-correlation Bell inequalities and network Bell inequalities, enabling the analytical derivation of optimal quantum violations and the conditions under which they occur. We further quantify the upper bound on maximal violations achievable by arbitrary two-qubit mixed states in such networks, under separable measurements, and evaluate the noise robustness of the proposed inequalities via the visibilities of noisy states. Finally, we demonstrate that these inequalities can, in a device-independent manner, distinguish between network topologies of equal size that differ in the number of leaf nodes.

Instabilities of fluid-fluid interfaces occur in many forms within passive soft matter. Adding activity to one of the fluids can dramatically change the stability of the interface. Triggering active flows externally offers a unique opportunity to study the linear growth of the instability and quantitatively compare experiment and theory. We investigate the interfacial instability of a deformable three-dimensional active nematic liquid crystal droplet confined between two parallel plates. Spontaneous active flows drive the growth of undulations along the active/passive interface, with the mode number of the fastest-growing mode increasing with droplet radius and decreasing with gap height. Applying the lubrication approximation to a minimal nematohydrodynamic model reveals that the growth rates of the interfacial modes are determined by the active timescale and the relaxation timescales associated with liquid crystalline order as well as capillary and viscous stresses. We find multiple points of agreement between experiment and theory, including the shape evolution of individual droplets, the growth rates of unstable modes averaged across many droplets, and the extensional shear flows observed within droplets.

For high-intensity photon pair generation via spontaneous parametric down-conversion, phase matching or quasi-phase-matching must be realized. The most common method is to use periodically poled crystals, where quasi-phase-matching is achieved through the periodic modulation of the nonlinear susceptibility. In contrast to solid-state materials typically employed, an alternative approach is demonstrated here by using chiral ferroelectric nematic liquid crystals (FNLCs). It involves the spontaneous formation of a twisted periodic arrangement of liquid crystal molecules that depends only on the concentration of chiral dopants. This enables the rapid and scalable fabrication of nonlinear optical media with a tunable periodicity of the structure. We show that within only $20\mu \mathrm{m}$, we can enhance the signal by 2 orders of magnitude compared to the maximal achievable rate for the non-phase-matched case. This process enables us to achieve a significantly enhanced photon pair generation rate of over 1200 Hz/mW in a very short interaction length while simultaneously maintaining a high degree of polarization entanglement. These results establish chiral FNLCs as a versatile, reconfigurable, and low-cost platform for nonlinear and quantum photonics.

Strong light-matter coupling in Fabry-Pérot cavities can modify ground-state molecular reactivity, charge, and energy transport, while modifications to single-molecule properties have not been observed experimentally. The mechanisms and reproducibility of such effects remain contested, with conflicting theoretical predictions driven by differences in Hamiltonian choice and quantum state representation. Here, we clarify these theoretical ambiguities in the treatment of cavity-coupled molecular ensembles, by performing numerically exact quantum simulations with the ab initio light-matter Hamiltonian, treating electrons, nuclei, and cavity photons on equal footing. We investigate ensembles of the rotational-vibrational-electronic Shin-Metiu model using variational tree-tensor network quantum dynamics, capturing rovibronic couplings and anharmonicity. Embedding ensembles in a cavity induces local modifications of rotational, nuclear, and—more weakly—electronic observables in individual molecules. The extent of these modifications depends only on the per-molecule coupling strength up until each molecule reaches the ultrastrong coupling regime, which remains unattainable in practical Fabry-Pérot setups. Increasing ensemble size toward the thermodynamic limit causes these local modifications to vanish regardless of dipole self-energy inclusion. Nonetheless, global ground-state observables, such as light-matter coupling energy contributions (affecting overall polarizability) and cavity field displacement fluctuations, depend crucially on proper treatment of intermolecular and light-matter correlations, whereas intramolecular observables remain largely insensitive. These insights are crucial for guiding future investigations using approximate quantum treatments, and for the interpretation of experimental results in polaritonic chemistry.

In this work, we map noisy intermediate-scale quantum (NISQ)-friendly implementations of the noninteracting quantum cellular automata (QCA) to a circuit quantum electrodynamics (cQED) hardware. We perform both noiseless and noisy simulations of the QCA one-particle sector, namely, the quantum walk, on $N$-cycles and $N\times N$ torus graphs. Moreover, within this framework, we also investigate the search problem and present a circuit for preparing the W state (i.e., the Dicke state with Hamming weight 1) using only N − 1 $\sqrt{\text{iSWAP}}$ gates and no ancilla qubits. The noiseless simulations are conducted with the Qiskit Aer simulator, while the noisy simulations with C12 Quantum Electronics’ in-house noisy emulator, Callisto. We benchmark the performance of our implementations by analyzing the simulations via relevant metrics and quantities such as the state count distributions, the Hellinger fidelity, the ${\ell }^1$ distance, the hitting time, and the success probability. Our results demonstrate that the QCA framework, in combination with cQED processors, holds promise as an effective platform for early NISQ implementations of quantum walk and quantum walk search algorithms.

We propose a physical framework for ant navigation of chemical trails. For this, we use controlled experiments in which individuals follow narrow pheromone trails, for which ants display oscillatory motion, as previously reported in the literature. We model this behavior by treating chemotaxis as an effective magnetic interaction between the ants’ velocity and the local chemical gradient. Under suitable approximations, the model yields an analytical expression for the velocity correlations in the direction perpendicular to the trail, predicting an underdamped oscillatory decay. This theoretical prediction is in qualitative agreement with our experimental measurements, indicating that the model captures the essential dynamical features of ant trail following. We fit the model parameters to individual trajectories in order to assess the consistency of the underlying assumptions, finding the same parameter relationship in both theory and experiment. Our results contribute to the characterization of chemotactic navigation in ants and illustrate how physical modeling can provide mechanistic insights into complex biological dynamics.

Although spatial resolution in fluorescence microscopy and related fields has advanced to the nanometer scale, time resolution has remained essentially unchanged and is set by the camera system’s imaging time. Yet adequate time resolution is crucial for information acquisition about, for instance, dynamical processes in cells. This acquisition typically proceeds by analyzing biomolecular trajectories from single-particle tracking experiments, in terms of a standard discrete-time hidden Markov model. This type of analysis assumes, however, that subsampling time events that happen during imaging time can be neglected, which is rarely the case. To remedy this, we here introduce an algorithm that efficiently calculates the exact contribution of state switches to the likelihood of observed trajectories. This is made possible by our analytic derivation of generalized transition probabilities—which we call transition-accretion probabilities—that probabilistically capture unseen switching behavior during data acquisition. We do in-silico Bayesian model selection and parameter inference, and demonstrate that our subsampling time hidden Markov model approach outperforms the standard variant (applicable to slow kinetics). Our method and associated free-to-use software opens up for precise and reliable parameter estimation across a variety of single-molecule experiments, irrespective of the temporal resolution of the setup.

We introduce the concept of entanglement halos, a set of strongly entangled distant sites within the ground state of a quantum many-body system. Such halos emerge in starlike systems with exponentially decaying couplings, as we show using both free fermions and the spin-1/2 antiferromagnetic Heisenberg model. Depending on the central connectivity, entanglement halos may exhibit trivial and nontrivial symmetry-protected topological features. Our findings highlight how geometry and connectivity can generate complex entanglement structures with rich physical content, which can be experimentally accessible via state-of-the-art technologies.

We study the evolution of the kinetic energy (or gradient norm) of an incident linearly polarized monochromatic wave propagating in correlated random media. We explore the optical flux transverse to the mean Poynting flux at the paraxial-nonparaxial (vectorial) transition along with vortex counting. Here, by paraxial-nonparaxial transition we mean a gradual loss of validity of the paraxial approximation such that it is necessary to solve Maxwell-consistently employing the dyadic Green’s function. The vortex number appears to increase approximately with a cubic root of the propagation distance for sufficiently small correlation length. Furthermore, a kink appears in nucleation rate at the position of maximum scintillation upon increasing correlation length. A driven steady state is reached due to the filtering of evanescent waves upon propagation. Finally, we present the spectrum of the incompressible kinetic energy and how it evolves from the paraxial case to that of a (nonparaxial) random field.

We show that two Yukawa-SYK models with a weak tunneling contact can have an exotic hybrid superconducting thermofield-double-like state that is holographically dual to a traversable wormhole connecting two black holes with charged scalar hair. The hybrid superconducting thermofield-double/wormhole (TFD/WH) state is distinguishable by anomalous scaling of revival oscillations in the fermionic Green's function, but also in a unique Andreev revival in the anomalous Green's function. The existence of this TFD/WH state surprisingly shows that some quantum critical effects can survive the phase transition to superconductivity. This Andreev revival is in principle an accessible signature of the transition to the TFD/WH phase detectable in the ac Josephson current.

Accurate noise characterization is essential for reliable quantum computation. Effective Pauli noise models have emerged as powerful tools, offering a detailed description of the error processes with a manageable number of parameters, which guarantees the scalability of the characterization procedure. However, a fundamental limitation in the learnability of Pauli eigenvalues impedes a full high-accuracy characterization of both general and effective Pauli noise models, thereby restricting, e.g., the performance of noise-aware error mitigation techniques. We introduce multilayer cycle benchmarking (MLCB), an enhanced characterization protocol that improves the learnability associated with effective Pauli noise models by jointly analyzing multiple layers of Clifford gates. We show a simple experimental implementation and demonstrate that, in realistic scenarios, MLCB can reduce unlearnable noise degrees of freedom by up to $75\%$, improving the accuracy of sparse Pauli-Lindblad noise models and boosting the performance of error mitigation techniques like probabilistic error cancellation. Our results highlight MLCB as a scalable, practical tool for precise noise characterization and improved quantum computation.

We introduce a general approach for probing nonlinear x-ray propagation by imaging secondary fluorescence emitted transverse to the driving field. When a short, intense x-ray pulse excites a deep $1s$ core orbital, subsequent $\mathrm{K}\alpha$ emission from spin-orbit-split $2p$ states can undergo stimulated amplification. This nonlinear process reshapes the relative populations of the $2p_{1/2}$ and $2p_{3/2}$ levels along the propagation path, leaving distinct signatures in the delayed L-edge fluorescence. By solving the coupled density-matrix and Maxwell equations, we show that these fluorescence signals provide a direct and experimentally accessible probe of x-ray amplification dynamics. We demonstrate the concept for argon atoms and extend it to molecular systems containing third-row elements, where competing effects of lifetimes, transition intensities, and nonresonant absorption determine the efficiency of stimulated emission. Our results establish L-edge fluorescence as a broadly applicable diagnostic of nonlinear x-ray phenomena, opening opportunities for studying light-matter interactions in regimes where direct detection of amplified x-ray signals is technically challenging.