The efficacy of a communication network hinges upon both its physical architecture and the protocols that are employed within it. In the context of quantum communications, there exists a fundamental rate-loss trade-off for point-to-point quantum channels such that the rate for distributing entanglement, secret keys, or quantum states decays exponentially with respect to transmission distance. Quantum networks are the solution to overcome point-to-point limitations, but they simultaneously invite a challenging open question: How should quantum networks be designed to effectively and efficiently guarantee high rates? Now that performance and physical topology are inexorably linked, this question is not easy, but the answer is essential for a future quantum internet to be successful. In this work, we offer crucial insight into this open question for complex optical-fiber quantum networks. Using realistic descriptions of quantum networks via random network models and practical end-to-end routing protocols, we reveal critical phenomena associated with large-scale quantum networks. Our work reveals the weaknesses of applying single-path routing protocols within quantum networks, observing an inability to achieve reliable rates over long distances. Adapting algorithms for multipath routing, we employ an efficient and practical multipath routing algorithm capable of boosting performance while minimizing costly quantum resources.

A 20-nm-wide (100)-oriented HgTe quantum well (QW) hosts a two-dimensional (2D) semimetal comprising both electrons and holes. In this study, we report that in addition to the previously observed quadratic temperature dependence of resistance, the system also displays an unexpected linear temperature dependence within specific top-gate voltage ranges. To account for this behavior, we extend the existing theoretical framework for temperature-dependent resistance in HgTe QW-based 2D semimetals with a focus on electron-hole scattering at low temperatures. Using the Boltzmann transport equation, we investigate the role of electron-hole interactions in this 2D semimetal. Our calculations reproduce a resistivity temperature dependence that aligns closely with experimental data. These findings establish this system as a robust platform for exploring interaction-limited transport regimes in a two-component plasma, particularly in the presence of disorder.

An important goal for swarming research is to create methods for predicting, controlling, and designing swarms, which produce collective dynamics that solve a problem through emergent and stable pattern formation, without the need for constant intervention and with a minimal number of parameters and controls. One such problem involves a swarm collectively producing a desired (target) density through local sensing, motion, and interactions in a domain. Here, we take a statistical physics perspective and develop and analyze a model wherein agents move in a stochastic walk over a networked domain, so as to reduce the error between the swarm density and the target, based on local, random, and uncertain measurements of the current density by the swarming agents. Using a combination of mean-field, small-fluctuation, and finite-number analysis, we are able to quantify how close and how fast a swarm comes to producing a target as a function of sensing uncertainty, stochastic collision rates, numbers of agents, and spatial variation of the target.

Models of spontaneous wavefunction collapse explain the quantum-to-classical transition without invoking the von Neumann measurement postulate. Prominent frameworks, such as the Diósi-Penrose (DP) and continuous spontaneous localization (CSL) models, propose a continuous, spontaneous measurement of the mass density field of quantized matter. We show that this mechanism could link both models—not just DP—to fundamental uncertainties in Newtonian gravity. Despite their nonrelativistic nature, these models suggest an induced uncertainty in the flow of time due to fluctuations in the Newtonian potential. We calculate the ultimate limit on time uncertainty and demonstrate that the resulting clock-time uncertainty remains negligible for all contemporary timekeeping devices, including atomic clocks.

Motivated by a putative model of black holes as quantum objects, we consider what types of operators would have a corresponding spectrum. We find that there are indeed such operators, but of a rather unusual type, and for which the wave functions are only barely localized. We point out a tension between such almost delocalized states and black holes as compact objects.

Based on an established relation that relates the integrated correlation functions for a trapped system to the infinite volume scattering phase shifts through a weighted integral, we propose to extract the infinite volume scattering phase shifts through quantum simulation of the integrated correlation functions of trapped two-particle systems on quantum computers. The integrated correlation function can be computed by an ancilla-based algorithm. The proposal is demonstrated with a simple contact interaction fermion model.

High-order harmonic generation via single-slit diffraction of relativistic laser pulses is investigated. Using fully kinetic two-dimensional (2D) and three-dimensional (3D) particle-in-cell simulations, we show that interesting optical phenomena emerge, including the generation of harmonic beams that are anomalously polarized orthongal to the driver, harmonic spectrum variation depending on the incident laser polarization, and a deflection of transmitted lights that leads to a tilted harmonic intensity pattern due to total angular momentum conservation. It is shown that these anomalous effects are associated with complex peripheral electron dynamics on the plasma vacuum interface. To account for these effects, a new theoretical model is developed that can calculate harmonic fields from arbitrary 2D electron motion within the diffraction plane based on the “relativistic oscillating window” mechanism; the results agree well with the simulations. Our model indicates that the optical properties of the harmonic beams are determined by the 2D in-plane electron motion, which can be leveraged to provide immense opportunities for manipulating light-matter interaction at relativistic intensities.

Symmetry is fundamental to physical laws across different scales—from spacetime structure in general relativity to particle interactions in quantum field theory. Local symmetries, described by gauge theories, are central to phenomena such as superconductivity, topological phases, and the Standard Model of particle physics. Emerging simulation techniques using tensor network states or quantum computers offer exciting possibilities of exploring the physics of these gauge theories, but require careful implementation of gauge symmetry and charge-neutrality constraints. This is especially challenging for non-Abelian gauge theories such as quantum chromodynamics (QCD), which governs the strong interaction between quarks and gluons. In a recent article (Than et al., arXiv:2501.00579), we introduced “charge-singlet measurements” for quantum simulations, consisting of a projection-based technique from group representation theory that allowed us to probe for the first time the phase diagram of ($1+1$)-dimensional QCD on a quantum computer. In this article, we show more broadly how to apply charge-singlet measurements as a flexible tool for both classical and quantum simulations of discrete and continuous gauge theories. Our approach extends the use of charge-singlet measurements beyond state preparation in the charge neutral (charge-singlet) sector to include noise mitigation in symmetry-preserving time-evolution circuits. We further demonstrate how this method enables the computation of thermodynamic observables—such as entropy—within the charge-singlet subspace, providing a tool for exploring the connection between quantum thermodynamics and gauge symmetry.

Exchange-only (EO) qubits, implemented in triple-quantum-dot systems, offer a compelling platform for scalable semiconductor-based quantum computing by enabling universal control through purely exchange interactions. While high-fidelity single- and two-qubit gates have been demonstrated, the synthesis of efficient multiqubit operations—such as the Toffoli gate—remains a key bottleneck. Conventional gate decompositions into elementary operations lead to prohibitively long and error-prone pulse sequences, limiting practical deployment. In this work, we introduce a gradient-based optimization algorithm, Jenga-Krotov (JK), tailored to discover compact, high-fidelity EO gate sequences. Applying JK to the Toffoli gate, we reduce the number of required exchange unitaries from 216 (in direct decomposition) to 92, and compress the time steps required from 162 to 50, all while maintaining target fidelity. Under realistic noise, the accumulated gate error from our optimized sequence is an order of magnitude lower than that of conventional approaches. We have also applied the JK algorithm to other multiqubit gates and algorithm. For the Fredkin gate, it reduces the number of time steps from 200 to 104 and the number of exchange unitaries from 276 to 172. For the quantum Fourier transform, it compresses the sequence from 180 to 80 time steps and from 237 to 202 exchange unitaries. These results demonstrate that the JK algorithm is a general and scalable strategy for multiqubit gate synthesis in EO architectures, potentially facilitating realization of multiqubit algorithms on semiconductor platforms.

We present a shortcuts-to-adiabaticity protocol to load a spin-polarized ultracold Fermi gas from the ground ($s$) band into the first excited ($p$) band of a one-dimensional optical lattice. In contrast to a Bose-Einstein condensate in a shallow lattice—whose narrow quasimomentum distribution admits uniform lattice modulation—a noninteracting Fermi gas occupies the entire first Brillouin zone, rendering high-efficiency transfer across all momentum classes exceptionally challenging. To address this, we cast the loading process as a global, multiparameter optimization problem: We jointly optimize the timing of lattice-depth pulses and the corresponding phase shifts to maximize the ensemble-averaged transfer fidelity over all quasimomentum states. We demonstrate that fine phase tuning dramatically enhances loading efficiency, though the mean fidelity systematically decreases as more quasimomentum modes are occupied. Finally, we benchmark our shortcuts-to-adiabaticity protocol against established high-band-loading methods, underscoring its minimal hardware requirements and submillisecond timescales. Our work provides a practical path for rapid, high-fidelity preparation of Fermi gases in excited lattice orbitals, opening avenues for exploring orbital dynamics, anisotropic interactions, and many-body phenomena.

The collective-flow-assisted nuclear shape-imaging method in ultrarelativistic heavy-ion collisions (UHICs) has recently been used to characterize nuclear collective states. In this paper, we assess the foundations of the shape-imaging technique employed in these studies. We argue that some current UHIC nuclear imaging techniques neglect fundamental aspects of spontaneous symmetry breaking and symmetry restoration in colliding ions and incorrectly infer one-body multipole moments from studies of nucleonic correlations. Therefore, the impact of this approach on nuclear structure research has been overstated. Conversely, efforts to incorporate existing knowledge on nuclear shapes into analysis pipelines can be beneficial for benchmarking tools and calibrating models used to extract information from ultrarelativistic heavy-ion experiments.

We study a class of bifurcations generically occurring in dynamical systems with nonmutual couplings ranging from models of coupled neurons to predator-prey systems and nonlinear oscillators. In these bifurcations, extended attractors such as limit cycles, limit tori, and strange attractors merge and split in a similar way as fixed points in a pitchfork bifurcation. We show that this merging and splitting coincide with the coalescence of covariant Lyapunov vectors with vanishing Lyapunov exponents, a feature that generalizes the exceptional points that can exist in families of non-Hermitian matrices or operators. We distinguish two classes of bifurcations associated with generalized exceptional points, corresponding respectively to continuous and discontinuous behaviors of the covariant Lyapunov vectors at the transition depending on the presence of a ${\mathbb{Z}}_2$ symmetry. We outline some physical consequences of this class of theories exhibiting generalized exceptional points, including nonreciprocal responses, the destruction of isochrons, and anomalous noise effects. In particular, we show that the effective diffusion coefficient on the attractor can stay finite or even diverge when the noise strength vanishes. We illustrate our results with concrete examples from neuroscience, ecology, and physics.

Entrainment refers to the unidirectional synchronization of an oscillator system to external periodic forcing, with phase-locking regions forming Arnold tongues. In some specific models, the hysteresis phenomenon of Arnold tongue has been observed, but methods to actively induce it across models are still lacking. In this study, we show that adaptive responses to periodic forcing can induce explosive entrainment, a phenomenon of sudden locking to an external frequency accompanied by significant hysteresis. In contrast to explosive synchronization, where synchronization emerges suddenly due to internal coupling, explosive entrainment describes the sudden locking to a given frequency caused by external forcing. Therefore, explosive entrainment is more likely to occur in systems where internal couplings are weak or difficult to estimate, but external forcing can be applied. Furthermore, we demonstrate the universal emergence of explosive entrainment in the Kuramoto model, Poincaré model, chaotic Rössler model, and complex Ginzburg-Landau equation. Theoretical hysteresis bounds in the Kuramoto model are determined based on analytical results of the Ott-Antonsen reduction method. This study provides ideas for actively inducing hysteresis through external forcing.

This paper presents a detailed numerical investigation of the deformation dynamics of spherical tin (Sn) microdroplets under the action of laser prepulses, which is an essential process for optimizing extreme ultraviolet (EUV) lithography targets. A hybrid simulation method is developed, combining a single-fluid radiation hydrodynamics model for laser-produced plasmas with a two-phase flow model that incorporates surface tension effects. Two distinct scenarios are analyzed using this hybrid approach: nanosecond and picosecond prepulses, each characterized by markedly different energy deposition and deformation mechanisms. The simulations capture the full deformation process from initial laser impact to the capillary timescale, reproducing target morphologies that show good agreement with experimental observations. Detailed quantitative analyses of droplet expansion rates and geometries are also provided. Finally, the impact of the predeformed targets on EUV emission performance is evaluated by simulating the interaction of a $\mathrm{C}{\mathrm{O}}_2$ main pulse with the deformed structures. This study offers significant insights into laser-droplet interactions and contributes to the development of precise control strategies for optimizing EUV target shaping.

Active matter systems serve as a paradigm for diverse nonequilibrium phenomena. Macroscopic realizations of active particles may exhibit inelastic collisions. We study the restitution coefficient dependence of the pressure exerted by a single bristlebot, a type of macroscopic driven particle with hopping dynamics. The finite hopping time allows for low- and high-drag parameter regimes. For low drag, the bristlebot pushes the wall with a momentum transfer rate $\dot{I}$ that satisfies $\dot{I}\simeq F$, where $F$ is the active force, in agreement with results for soft (elastic) walls. In the high-drag regime, we find $\dot{I}\propto (1+r)F$, showing dependence on the coefficient of restitution $r$. This behavior can be understood analytically by studying the periodic solutions of a simple one-dimensional model. Numerical simulations show that the transition between two regimes also exists for highly active two-dimensional particles.

A healthy brain exhibits a rich dynamical repertoire, with flexible spatiotemporal patterns replaying on both microscopic and macroscopic scales. We hypothesize that the observed relationship between empirical structure and functional patterns is best explained when the microscopic neuronal dynamics is close to a critical regime. Using a modular spiking neuronal network model based on empirical connectomes, we posit that multiple stored functional patterns can transiently reoccur when the system operates near a critical regime, generating realistic brain dynamics and structural-functional relationships. The connections in the model are chosen so as to force the network to learn and propagate suited modular spatiotemporal patterns. To test our hypothesis, we employ magnetoencephalography and tractography data from five healthy individuals. We show that the extended critical region of the model maximizes the structure-function correlation and generates realistic features, demonstrating the relevance of near-critical regimes for physiological brain activity.

High-dimensional (HD) quantum entanglement expands the Hilbert space, offering a robust framework for quantum information processing with enhanced capacity and error resilience. In this work, we present an HD frequency-domain entangled state, the hybrid frequency-entangled qudit (HFEQ), generated via Hong-Ou-Mandel (HOM) interference, exhibiting both discrete-variable (DV) and continuous-variable (CV) characteristics in the frequency domain. By tuning HOM interference, we generate and control HFEQs with dimensions $D=5,7,9,$ and 11, confirming their DV nature. Franson interferometry verifies global frequency correlations with a visibility of $97.6\pm 0.6\%$ and CV entanglement within individual frequency modes with a visibility exceeding $95\%$. Furthermore, based on the developed theoretical model, the generated HFEQs exhibit a Schmidt number that exceeds the upper bound $D$ of conventional frequency-entangled qudits, certifying additional entanglement inherent to the hybrid structure. Our findings provide deeper insight into the physical nature of frequency-entangled qudits generated by quantum interference and introduce a resource for HD time-frequency quantum information processing.