We present the first experimental investigation of deuteron fusion at thermal energy performed underground. Using deuterated palladium targets, we measured spontaneous proton emission attributed to nuclear fusion reactions between deuterons. Protons with energies around 3 MeV, consistent with the expected signature of the deutron-deutron fusion reaction, were observed in palladium foils. Despite extensive efforts, we found no evidence for the predicted $0^{+}$ resonance near the reaction threshold.

We introduce graphene nanohelicoids, geometric analogs of graphene nanoribbons, in which the honeycomb lattice is embedded on a helicoidal surface. Starting from the three-dimensional helical structure, we construct effective one-dimensional lattice models with band structures characterized by a momentum-shifted particle-hole relation $E_v\left(k\right)=-E_c(k+\pi )$ that reflects an antichiral symmetry arising from the nonsymmorphic symmetry. A systematic investigation of graphene nanohelicoids using the tight-binding approximation reveals a number of trends upon varying width and edge orientation, for instance, alternating transitions between semiconducting and metallic regimes. As the structure width varies, the band gap periodically closes and reopens, accompanied by an alternating Zak phase that switches between trivial and nontrivial. Using an analytic tight-binding model with a continuous deformation of the graphene nanohelicoids, we explain the origin of width- and termination-dependent band inversion and alternating Zak phase, and derive the relationship between the termination-resolved index and the sublattice symmetry operator in one-dimensional nonsymmorphic systems.

Large optical coherent-state superpositions are essential to advance quantum sensing, quantum repeaters, and error-correction codes. We propose a deterministic feedforward protocol employing qubit-mode dispersive coupling, currently available in cavity quantum electrodynamics (QED). We show this single-mode protocol to outperform the advanced three-mode Gaussian-photon-number-resolving detector scheme in terms of both average fidelity and quantum non-Gaussian phase-space properties, and propose sensitivity to weak displacements of interference fringes as a feasible and conclusive witness of quantum interference. This approach combining QED with electro-optical feedforward is extendable to tailored states for applications and other platforms.

We report a combined microfocused angle-resolved photoemission spectroscopy and first-principles study of the rare-earth tetraborides ${R\mathrm{B}}_4$ $(R=\mathrm{Tb}, \mathrm{Gd})$, which host a Shastry-Sutherland lattice. We identify extended bulk nodal lines at the tetragonal Brillouin-zone boundaries, whose fourfold degeneracies are enforced by the nonsymmorphic glide-mirror symmetries even in the presence of spin-orbit coupling (SOC), unlike conventional nodal lines that SOC typically gaps. Systematically evolving Dirac-like dispersions resolved by momentum-distribution-curve analysis support this symmetry-enforced nodal line. We further identify a related nodal-line feature that disperses toward the Fermi level $\left(E_{\text{F}}\right)$; although the calculated SOC-induced gap for this feature (0.2–4.6 meV) lies below the experimental resolution, its proximity to $E_{\text{F}}$ offers a band-structure basis consistent with the emergence of large magnetoresistance. First-principles Wilson-loop calculations establish a nontrivial $\pi$ Berry phase for the bulk nodal line, and we observe a photon-energy-independent surface-derived feature whose dispersion is consistent with the calculated surface state. Our results identify ${R\mathrm{B}}_4$ as a platform for nonsymmorphic-symmetry-enforced nodal-line physics with potential relevance to large magnetoresistance and topological surface states.

We study the matter and entropy transport between two ultracold neutral Fermi-gas reservoirs linked by a quantum point contact under a chemical-potential gradient. We describe the two leads with a BCS mean-field model and derive the current-bias characteristics for both particle and entropy transport. We compute the out-of-equilibrium steady-state currents by using the Keldysh formalism. In accordance with previous works in the literature, we confirm the well-known behavior for the particle current and extend the computation to the entropy current in the BCS regime. The entropy current shows an oscillatory behavior at low voltage in the ballistic junction limit. We analyze the results for a wide range of values of the junction's transparency. We also compare our findings with experimental results in cold atomic gases in the unitary regime.

Light possesses both spin and orbital angular momentum. In spatially inhomogeneous optical fields, which are characterized by a finite distribution of wave vectors in $k$ space, these properties undergo spontaneous coupling, referred to as optical spin-orbit coupling. The study of the coupling has recently become central in modern optics due to its substantial applications in communications, sensing, and quantum control. A key challenge is to clarify the relationship between the origins of spatially inhomogeneous optical fields and the resulting spin-orbit coupling. Current research focuses on materials and configurations exhibiting spatial inhomogeneity, such as focusing lenses, interfaces, inhomogeneous media, and metasurfaces. However, Maxwell’s equations indicate that matter can introduce both spatial inhomogeneity and temporal asymmetry into optical fields. For instance, magnetic ordering breaks the time-reversal symmetry of interacting optical fields via the magneto-optic effect, introducing nonreciprocity in the resulting optical phenomena. Despite the importance, optical phenomena involving both spatially inhomogeneous and temporally asymmetric optical fields remain unexplored. Here, we demonstrate that combining temporal asymmetry and spatial inhomogeneity through magnons and light focusing, respectively, transforms an input Gaussian beam into a specific optical vortex beam in a nonreciprocal manner. This phenomenon is quantitatively explained by integrating the physics of magnon-induced Brillouin light scattering with optical spin-orbit coupling. The observed conservation of total angular momentum, encompassing both magnons and photons, further indicates that magnons can control both spin and orbital angular momentum of light. Finally, we outline future research directions enabled by optical fields exhibiting both spatial inhomogeneity and temporal asymmetry.

We introduce an experimental technique for achieving an unprecedented energy resolution in attosecond interferometry. Using a second-harmonic bandwidth compressor, we create narrow-band ($<1\mathrm{nm}$), tunable femtosecond pulses that generate high harmonics with a bandwidth of 50–73 meV, achieving the highest energy resolution in any attosecond time-resolved measurement, sufficient to resolve the spin-orbit splitting of the ${}^2\mathrm{P}$ ground state of ${\mathrm{Ar}}^{+}$. The fine tunability of these pulses resolves a 10-as variation of the spin-orbit photoionization delay across the [Ne]$3{\mathit{s}}^{1}3{\mathit{p}}^{6}5\mathit{p}$ resonance of neutral Ar. Calculations based on the relativistic random-phase approximation with exchange, with qualitative inclusion of shakeup configurations, reveal the importance of spin-orbit and electron-correlation effects to accurately reproduce and interpret photoionization delays.

We obtain the exact many-body density operator of a boundary-driven XXZ quantum circuit via a spatially inhomogeneous matrix product ansatz. The ansatz has formally infinite bond dimension and generalizes authors’ previous construction [Popkov and Prosen, Phys. Rev. Lett. 135, 070401 (2025)] for the XXZ interactions. The boundary qubits are coupled to reset quantum channels that project them toward arbitrary pure target states. We find and describe a family of relatively robust separable chiral nonequilibrium steady states, which are elliptic analogs of spin helices for the circuit, and which are particularly attractive from an experimental perspective.

Strong coupling between atomic ensembles and high-quality optical cavities enables collective and nonlinear phenomena that are central to cavity quantum electrodynamics (cQED). Many experiments have been performed on this topic, with most of them focusing on cold atoms. Here, we experimentally demonstrate collective strong coupling between thermal rubidium vapor and high-quality silicon nitride microring resonators (MRRs) on an integrated photonic chip. We observe cavity-mode splitting, with a measured collective coupling strength of $g_N/2\pi \approx 1\mathrm{G}\mathrm{Hz}$ and a collective cooperativity of $C_N\approx 2$ at $110{}^{\circ }\mathrm{C}$, indicating coherent energy exchange between the atomic ensemble and the cavity mode despite rapid decoherence in the thermal vapor system. We infer an average of 20 atoms effectively participating in the collective interaction, yielding a single-atom cooperativity of $C_0=0.1$ and approaching the single-atom strong-coupling regime. Our results establish the integrated thermal vapor MRR platform as a robust, compact, and scalable system for studying collective and nonlinear phenomena in cQED.

Epidemic spreading over population networks has been an important subject of research for several decades, especially during the Covid-19 pandemic. Most epidemic outbreaks are likely to create multiple mutations during their spreading over the population. In this paper, we study the evolution of a pathogen that can mutate continuously during the epidemic spreading. We consider pathogens whose mutating parameter is the mortality mean time and study the evolution of this parameter over the spreading process. We use analytical methods to compute the dynamic equation of the epidemic and the conditions for it to spread. We also use numerical simulations to study the pathogen flow in this case and to understand the mutation phenomena. We show that the natural selection leads to less violent pathogens becoming predominant in the population. We discuss a wide range of network structures and show how different effects are manifested in each case. We also applied our theory in the context of the Covid-19 pandemic, using relevant epidemiological data collected for this outbreak. We provided insights for the variants spreading processes observed throughout this pandemic.

Brownian circuits perform computations using stochastic transitions driven by thermal fluctuations. While the energetic costs of such fluctuation-driven computation have been extensively studied within stochastic thermodynamics, much less is known about its computational complexity, in particular, how computation time scales with circuit size. In this work, the computation time for explicitly designed Brownian circuits is numerically investigated via the first-passage time to a completed state. For arithmetic circuits such as adders, varying the forward transition rate induces a sharp change in the scaling behavior of the mean computation time with circuit size, from linear to exponential. This change can be interpreted as an easy-hard transition in computational time complexity. The transition suggests that, for meaningful computational tasks, achieving efficient polynomial-time computation generally requires a finite forward bias corresponding to a nonzero energy input. As a counterexample, we show that arbitrary logical operations can be reduced to an effective one-dimensional stochastic process in which the zero-bias limit lies within the computationally efficient (easy) regime. However, achieving such a one-dimensional normal form unavoidably leads to an exponential increase in circuit size. These results reveal a fundamental trade-off between computation time, circuit size, and energy input in Brownian circuits and demonstrate that phase transitions in time complexity provide a natural framework for characterizing the cost of fluctuation-driven computation.

Direct experimental access to orbital states in strongly correlated materials remains a major challenge, despite their central role in driving coupled structural and magnetic phase transitions. In systems where electronic correlations, electron-lattice coupling, and relativistic spin-orbit interactions compete on comparable energy scales, first-principles calculations often yield multiple metastable solutions, hindering the unambiguous identification of the ground state. Here, we demonstrate that the orbital states of the spinel oxide ${\mathrm{FeV}}_2{\mathrm{O}}_4$, which possesses active orbital degrees of freedom on both Fe and V ions, are uniquely resolved by combining valence electron density (VED) analysis based on state-of-the-art synchrotron x-ray diffraction with spin-polarized density-functional-theory calculations. Our results reveal that temperature-dependent rearrangements of orbital occupations drive successive structural transitions that accompany collinear and noncoplanar ferrimagnetic ordering, establishing a direct correspondence between orbital anisotropy and spin structure. This work shows that experimentally determined VED provides a decisive real-space constraint on competing theoretical solutions, offering a powerful and broadly applicable framework for elucidating the microscopic mechanisms of complex phase transitions in strongly correlated electron systems.

Superconducting (SC) pairing mechanism, origin of high $T_c$, and symmetry of SC order parameter in Fe-based superconductors are among the important unsolved problems in condensed matter and materials physics. We study the SC properties of ThFeAsN, an Fe-based high-$T_c$ superconductor, by ab initio superconducting density functional theory calculations with electron-phonon coupling, screened static and dynamic electron-electron Coulomb repulsion, and spin fluctuation (SF)-mediated pair interaction fully taken into account. Our calculations reveal that ThFeAsN is an SF-mediated multiband superconductor with the calculated $T_c$ of 22.4 K and the $d_{xy}$-wave SC order parameter with different signs on different Fermi surface sheets, consistent with most experiments. We also present distinct SC properties such as quasiparticle density of states and ultrasonic attenuation coefficient, which can be immediately verified by experiments.

We present a hardware-native gadget framework for solving constraint-satisfaction problems on Rydberg quantum computing architectures. Our approach introduces a compact ${\text{xor}}_1$ gadget that enforces exactly-one constraints, ubiquitous in combinatorial optimization, directly through geometric embedding and blockade interactions. A key advantage of the ${\text{xor}}_1$ gadget is its fixed, problem-size-independent detuning requirements: Enforcing constraints through blockade interactions eliminates the need for large penalty terms, thereby substantially reducing the detuning range compared to quadratic unconstrained binary optimization (QUBO) formulations and improving experimental feasibility. By tailoring the construction to the geometric connectivity of Rydberg-atom arrays, the framework bypasses the all-to-all physical couplings often assumed in logical encodings. This enables embeddings compatible with planar layouts and avoids highly connected arrangements. We develop scalable implementations that reduce atom count and connectivity overhead while avoiding extensive classical preprocessing, making them compatible with near-term neutral-atom hardware. As illustrations, we apply our framework to the gate-assignment and $N$-queen problems, highlighting its practicality, resource efficiency, and hardware compatibility. In these examples, we observe reductions in detuning range of up to $99\%$ and savings in atom count and connectivity overhead of up to $54\%$ compared to the QUBO method. These results establish a route toward implementing large-scale combinatorial optimization on Rydberg platforms beyond the limits of existing encodings.

Remote synchronization, in which indirectly connected nodes synchronize while the mediating hub remains desynchronized, is a counterintuitive form of collective dynamics in complex networks. Most previous studies have treated each node as a single oscillator, whereas nodes in realistic systems often represent populations of interacting dynamical units. Here, we study remote synchronization in a star network whose nodes are Kuramoto oscillator populations. Each node contains many internally coupled oscillators with coupling strength $K$, and different nodes interact through an internode coupling strength $L$. We show that remote synchronization emerges only at an intermediate level of internal synchrony: The leaf nodes become strongly synchronized with each other, while the hub remains weakly synchronized with them, when the internal order parameter is neither close to zero nor close to one. Increasing $K$ further causes an abrupt breakdown of the remote-synchronized state. Detrended fluctuation analysis reveals enhanced scaling behavior and critical-like long-range temporal correlations near this breakdown boundary. A two-parameter scan in the $(L,K)$ plane confirms that the remote-synchronized regime occupies a finite region associated with intermediate internal order and relatively low detrended fluctuation analysis exponent. We further provide a phenomenological effective-phase interpretation, showing that internal coupling controls the coherence, susceptibility, and stability of each oscillator population. These results demonstrate that internal population dynamics can regulate both the emergence and critical-like breakdown of remote synchronization.

Earthquake diffusion is commonly interpreted either as the migration of fluids or as the propagation of triggering cascades within branching processes. In the latter framework, anomalous diffusion emerges naturally from the long-memory kernels of epidemic-type aftershock sequence (ETAS) models. Here, we introduce a swarm-informed ETAS (SIETAS) model designed to describe volcanic seismic swarms. The model combines a temporally truncated power-law triggering kernel with a spatially localized logistic kernel, thereby introducing intrinsic temporal and spatial scales into the triggering process. Using an AI earthquake catalog from the ongoing Campi Flegrei unrest, we show that SIETAS provides a substantially better description of seismicity than the standard ETAS formulation. We further demonstrate that earthquake diffusion exhibits clear multiscaling behavior characterized by three effective scaling regimes. Analytical arguments based on branching-process theory and continuous-time random walks indicate that the SIETAS kernels generate a crossover from transient anomalous diffusion to an effectively normal-diffusive regime, followed by saturation due to finite subcriticality. We discuss how the observed multiscaling behavior may emerge from the interplay between short-time triggering, finite temporal memory, finite spatial localization, and secondary components of the triggering kernel. These results establish a connection between swarm-informed earthquake triggering and multiscale diffusion phenomena in volcanic environments.

Gaussian baths are widely used to model non-Markovian environments, yet the cost of accurate simulation at long times remains poorly understood, especially when spectral densities exhibit nonanalytic behavior as in a range of realistic models. We rigorously bound the complexity of representing bath correlation functions on a time interval $[0,T]$ by sums of complex exponentials, as employed in recent variants of pseudomode and hierarchical equations of motion methods. These bounds make explicit the dependence on the maximal simulation time $T$, inverse temperature $\beta$, and the type and strength of singularities in an effective spectral density. For a broad class of spectral densities, the required number of exponentials is bounded independently of $T$, achieving time-uniform complexity. The $T$ dependence emerges only as polylogarithmic factors for spectral densities with strong singularities, such as step discontinuities and inverse power-law divergences. The temperature dependence is mild for bosonic environments and disappears entirely for fermionic environments. Thus, the main bottleneck for long-time simulation is the presence of sharp nonanalytic features in the bath spectrum. Our results are instructive both for long-time simulation of non-Markovian open quantum systems and for Markovian embeddings of classical generalized Langevin equations with memory kernels.

Dynamical instabilities can amplify small perturbations into measurable signals, offering a route to quantum-enhanced sensing. This mechanism was experimentally demonstrated in a collective spin system with quadratic interactions, described by a twist-and-turn Hamiltonian, where quantum evolution near an unstable point leads to exponential growth of spin fluctuations, enabling metrological gain beyond the standard quantum limit. Here, we show that a quartic extension of this Hamiltonian substantially increases the amplification. This additional nonlinear term reshapes the phase-space structure, generating new unstable fixed points with larger local Lyapunov exponents and therefore faster signal amplification at shorter evolution times. Remarkably, even for the same instability rate (equal Lyapunov exponent), collective multibody interactions outperform the quadratic case, demonstrating that metrological gain is not determined by the Lyapunov exponent alone. We show analytically that the finite-time growth of the gain is governed also by the local phase-space curvature around the unstable point. Only for a symmetric unstable point, as in the quadratic case, is the finite-time gain described by the Lyapunov exponent alone. Our results identify local phase-space curvature as an additional resource for optimizing the speed and performance of quantum sensors.

Bubble-shaped Bose-Einstein condensates (BECs) constitute a unique class of quantum fluids with a hollow, thin-shell geometry that supports a wide variety of phenomena distinct from those of compact condensates. Numerical simulation of such systems is particularly challenging due to their inherently three-dimensional structure and extreme aspect ratios. We present an efficient finite-difference simulation framework for solving partial differential equations in nontrivial topologies, with a focus on the static and dynamical modeling of bubble-shaped BECs. By employing selective spatial sampling on a semistructured grid, our method substantially reduces memory usage and achieves more than an order-of-magnitude improvement in computational performance compared with conventional split-step Fourier solvers. The algorithm is naturally extendable to highly parallel execution on graphics processing units (GPUs), enabling large-scale, time-dependent simulations of thin-shell condensates. We apply this framework to simulate the formation of bubble BECs through a controlled hollowing-out protocol using ab initio trapping potentials relevant to the Cold Atom Laboratory aboard the International Space Station. From these simulations, we identify characteristic timescales and parameter ramps required to achieve adiabatic evolution, thereby assessing the feasibility of experimentally realizing bubble-shaped condensates in microgravity environments.