Material defects give rise to parasitic two-level systems (TLS) that present a major source of decoherence in superconducting qubits. Here, we study a strongly coupled TLS that resides in the tunnel barrier of transmon qubit. We use multiphoton spectroscopy and TLS strain tuning to explore the rich spectrum of the interacting three-partite system consisting of TLS, qubit, and its readout resonator. This reveals a strong effective resonant coupling between the TLS and the qubit's readout resonator, which dresses the resonator states and results in a resonance frequency shift that spoils the readout signal. Our finding presents yet another way how material defects can interfere with qubit operation and hinder the realization of solid-state quantum processors.

Drawing inspiration from swarm intelligence, we show that short-range attractive interactions between thermally driven Brownian quasiparticles enable energy-efficient optimization. As quasiparticles can be generated directly within a material, the swarm size can be adjusted with minimal energy overhead. Using an optimization task defined by a spatially varying temperature landscape, we quantitatively show that interacting swarms reliably identify global optima and significantly outperform noninteracting searchers within a well-defined regime of interaction strength and swarm size. This improvement arises from emergent cooperative behavior, where local interactions guide the swarm toward high-quality solutions without central coordination. To link our physical model to experimental realizations, we coarse grain the quasiparticle dynamics onto a sensor lattice and generate trajectories emulating particle-tracking measurements. We further show that the interacting swarm adapts robustly to landscapes that evolve over time. These findings establish interacting Brownian quasiparticles as a physical platform for scalable and energy-efficient unconventional computing.

The Ti $L_{2,3}\text{−}\mathrm{edge}$ x-ray absorption spectra of various titanium oxides, including perovskite $\mathrm{SrTi}{\mathrm{O}}_3$, rutile and anatase $\mathrm{Ti}{\mathrm{O}}_2$, and ilmenite $\mathrm{CoTi}{\mathrm{O}}_3$, are analyzed with particular attention to the energy range beyond the near-edge/charge-transfer region and up to the oxygen $K$ edge. We found that the spectral structure varies among materials and can be described using density functional theory without including the multielectron effects indispensable for describing near-edge and charge-transfer structures. We term the structures in this energy range the middle-range-energy structure and show that the distinct features are determined by the local atomic geometry around the target Ti atoms and, essentially, by the partial density of states of those atoms. Here, we demonstrate how to extract information from middle-range-energy structures by comparing them with ab initio calculations, and we propose this energy-range analysis as a new method for studying local atomic geometry, free of parameters describing multielectron effects.

We study the electronic structure and dynamical correlations in antiferromagnetic ${\mathrm{BiFeO}}_3$, a prototypical room-temperature multiferroic, using a variety of static and dynamical first-principles methods. Conventional static Hubbard corrections ($\mathrm{DFT}+U, \mathrm{DFT}+U+V$) incorrectly predict a deep-valence Fe $3d$ peak (around $-7\text{eV}$) in antiferromagnetic ${\mathrm{BiFeO}}_3$, in contradiction with hard x-ray photoemission. We resolve this failure by using a recent generalization of $\mathrm{DFT}+U$ to include a frequency-dependent screening—$\mathrm{DFT}+U\left(\omega \right)$—or using a dynamical Hubbard functional. The screened Coulomb interaction $U\left(\omega \right)$, computed with spin-polarized random-phase approximation and projected onto maximally localized Fe $3d$ Wannier orbitals, is expressed as a sum over poles, yielding a self-energy that augments the Kohn-Sham Hamiltonian. This $\mathrm{DFT}+U\left(\omega \right)$ approach predicts a fundamental band gap of $1.53\text{eV}$, consistent with experiments, and completely eliminates the unphysical deep-valence peak. The resulting simulated hard x-ray photoelectron spectroscopy spectrum reproduces the experimental line shape with an accuracy comparable to state-of-the-art approaches. Our work highlights the critical nature of dynamical screening in complex oxides and of $\mathrm{DFT}+U\left(\omega \right)$ as a predictive and computationally efficient approach to address the electronic structure of correlated materials.

We use spin dynamics simulations to determine the origin of the unusual correlated diffuse scattering, characterized by half-moon shapes bridging the magnetic Bragg peaks, observed in the polarized elastic neutron scattering from manganese tungstate, ${\mathrm{MnWO}}_4$. We first fit a Heisenberg Hamiltonian with 12 nearest-neighbor exchange interactions and single-ion anisotropy to the experimental ground-state magnon dispersion. We then show via spin dynamics simulations that our model Hamiltonian both reproduces the experimentally observed half-moon features and captures their persistence into the paramagnetic regime. Moreover, we identify the three-dimensional, competing antiferromagnetic interactions driving this behavior. Our work complements earlier studies of half-moon-shaped signatures in pyrochlore and triangular structures, by providing insight into their origin and showing that the half moons in ${\mathrm{MnWO}}_4$ result from three-dimensional competing exchange interactions, in the absence of the spin-liquid behavior with which they are usually associated.

We obtain an exact solution for the spectral function for one-dimensional Bose-Bose and Fermi-Fermi mixtures with strong repulsive interactions, valid in arbitrary confining potentials and at all frequency scales. For the case of harmonic confinement, we show that, on top of the ladder structure of the density excitations imposed by the external confinement, spin excitations emerge as sideband peaks, with dispersion related to the one of ferromagnetic or antiferromagnetic spin chains and a width fundamentally larger for fermionic mixtures than for bosonic ones, as determined by the different symmetry of spin-excited states. The observation of spin excitation branches can provide a univocal probe of interaction-induced magnetism in ultracold atoms.

Altermagnets are a novel class of magnetic systems characterized by their momentum-dependent spin splitting without net magnetization. In this work, we extend established Euclidean tight-binding models of altermagnets to regular hyperbolic lattices in two spatial dimensions defined on a discretized Poincaré disk. Using hyperbolic crystallography and Abelian hyperbolic band theory, we show that the inclusion of next-nearest-neighbor hopping is sufficient to induce spin splitting in minimal tight-binding models of bipartite hyperbolic lattices. While certain families and special cases of hyperbolic lattices remain antiferromagnetic, we identify an entire family and a special case that generically permit spin splitting in this framework. Hence, altermagnetism is inherent to certain hyperbolic lattices. Since Abelian hyperbolic band theory yields a momentum space that is at least four dimensional, we classify the leading spin-splitting harmonics using four-dimensional atomic orbitals. As an outlook, we apply non-Abelian hyperbolic band theory to the $\{10,5\}$ lattice. Although its Abelian spectrum is spin degenerate, two selected higher-genus supercells exhibit spin splitting. This finding suggests that spin degeneracy does not necessarily persist within all translation representation sectors.

End-to-end pumps utilizing edge-localized states offer a promising route to operate as connecting buses, supplying efficient and robust connectivity between non-neighboring elements in a network. Here, we investigate a finite quasiperiodic Fibonacci-type photonic chain and demonstrate its ability for end-to-end pumping, with only small and simple changes to the system. First, we use a tight-binding formalism to numerically show that a localized pumping state can be transferred between opposite ends of the system, with only a small structural change to the chain. Then, we experimentally implement this end-to-end pump in an array of coupled optical waveguides, where light propagation is effectively described by the tight-binding model under the paraxial approximation, enabling direct correspondence between theory and experiment. We numerically simulate and experimentally demonstrate pumping by injecting light into a single waveguide at one end of the setup, which activates a localized pumping state. As the light propagates along the waveguide array, it is also pumped to the other end. We further show that pumping remains robust against structural deformation, such as controlled defects in the waveguide array. Our results establish that quasiperiodic Fibonacci-type photonic lattices are a robust and experimentally viable platform for disorder-resilient state transfer.

Liquid-liquid phase separation underlies phenomena ranging from protein condensate formation to the phase coexistence of synthetic polymers. Although the random phase approximation (RPA) is widely used to predict such phase behavior, its quantitative accuracy for binodals of polymer solutions, particularly outside the high-density regime, remains incompletely characterized. Here, we develop a field-theoretic loop expansion in homopolymer systems by identifying the inverse polymer density ${\rho }^{-1}$ as the Planck constant $\hslash$ in quantum field theory. We calculate the leading-order and next-to-leading-order corrections to the RPA free energy, denoted as $\mathrm{RPA}+$ and $\mathrm{RPA}++$, respectively. Testing the binodal predicted by the $\mathrm{RPA}+$ against molecular dynamics simulations of bead-spring chains with Gaussian pair interactions, we find that the $\mathrm{RPA}+$ qualitatively improves the dilute-phase coexistence density over the RPA, while the critical point error remains comparable to that of the RPA. Our results establish the loop expansion as a systematic route for refining the RPA-based binodal predictions for polymer phase separation.

Hole-spin qubits enable fast, all-electrical spin manipulation through electric-dipole spin resonance (EDSR), arising from two microscopic mechanisms rooted in their intrinsically strong spin-orbit interaction. Depending on how the electric field acts on the quantum dot, the spin can be driven either by a modulation of its $g$ factor or by a displacement of the wavefunction. Here, we demonstrate in situ control over the dominant EDSR driving mechanism of a hole-spin qubit in a silicon fin field-effect transistor by applying microwave signals to two different gate electrodes, thereby tuning the orientation of the local electric field. We measure the effective $g$ factor, its electrical tunability, and the Rabi frequency as functions of magnetic-field orientation. Their distinct angular dependencies, analyzed using a $g$-matrix formalism, allow us to identify the underlying driving processes and track their relative contributions for different drive configurations. By selecting the drive electrode, we can switch from a regime dominated by $g$-factor modulation to one with a strong contribution from wavefunction displacement. This in situ tunability provides direct experimental access to both spin-driving mechanisms and offers a route toward optimized spin-qubit performance.

Photoinduced phase transition (PIPT) involves substantial changes in both electronic and crystallographic structures caused by electron excitations. Because PIPT is ultrafast and exhibits inhomogeneous behavior, its fundamental processes, in particular, how the ultrafast dynamics of photoexcited electrons trigger lattice deformation and the timescales involved, remain poorly understood. In this study, phase transition and its spatial separation in organic charge-transfer complexes was investigated using photoemission electron microscopy with femtosecond pulsed laser excitation. First, the thermally induced phase transition was confirmed by imaging the morphology change and also by observing the change of spectral shape around the Fermi level. Second, the escape time of photoexcited electrons or the heat generated by the laser pulses is estimated by observing the morphology change depending on the laser repetition rate. Finally, the dynamics of the photoexcited electrons and the subsequent morphology change are directly visualized. The results show that an anisotropic morphology change is initiated following the accumulation of electrons in unoccupied states over approximately a picosecond.

We show that anisotropic spin interactions do not merely break spin-space group (SSG) symmetries, but instead twist them through cohomology invariants, yielding symmetry classes beyond subgroups of $\mathrm{O}\left(3\right)\times Isom\left({\mathbb{R}}^3\right)$. This requires redefining the spin-only group ${\mathcal{S}}_0$ in terms of proper spin rotations. Based on this unitary ${\mathcal{S}}_0$, we formulate a twisted SSG (tSSG) theory that captures the complete set of spin-space symmetries. We then study a spin-1 model with tSSG symmetry using linear flavor wave theory and find ${\mathbb{Z}}_2$ topological quadrupolar excitations defined on a spin Brillouin Klein bottle. Specifically, the quadrupolar excitations possess a momentum-space glide-reflection symmetry and the edge states exhibit a nonlocal momentum twist. These results establish the symmetry language required for interacting spin systems, whether realized in magnetic materials or on programmable quantum simulators, and open a route to unconventional magnetism.

Efficient optomechanical cooling typically requires high photon occupancy to maximize cooling power, a constraint that generally limits the degree of coherent quantum control available in the few-photon regime. Here, we investigate this trade-off by considering a strongly nonlinear cavity operated as a discrete quantum system. In the weak-coupling limit, we derive a general connection between the optomechanical damping rate and the cavity's dressed-state manifold. This framework reveals that the damping rate (determined by the population imbalance across dressed states) is directly tunable via the coherent manipulation tools, which are standard in circuit quantum electrodynamics. We illustrate this framework using a Josephson photonics architecture, where a dc-biased junction induces a photon blockade that truncates the cavity to an $N$-level system. By sacrificing raw cooling (or heating) power, this platform enables full quantum mechanical control over optomechanical properties, offering a versatile avenue for the quantum manipulation of mechanical modes.

We uncover a previously unrecognized hierarchical algebraic structure in the Bose-Hubbard model that enables a systematic construction of its spectrum without relying on integrability. We develop a recursive framework in which, within each fixed particle-number sector, the eigenproblem of a $p$-site system is reduced to a closed set of algebraic relations determined entirely by the eigenpairs and single-particle transfer amplitudes of the $(p-1)$-site subsystem. This reduction yields two complementary sets of Bethe-type equations whose solutions exhaust the spectrum. The underlying structure originates from the locality of the Hamiltonian, which constrains the coupling between subsystems and gives rise to an emergent sparse, near-tridiagonal representation of the many-body problem. As an explicit demonstration, we construct the complete spectrum of the three-site Bose-Hubbard model from that of the two-site system for particle numbers $n\le 3$, obtaining exact agreement with direct diagonalization. The resulting formulation substantially reduces computational cost and reveals a form of hierarchical solvability in a nonintegrable quantum many-body system. More broadly, our results suggest that recursive algebraic constructions may provide a general framework for analyzing lattice models beyond the conventional integrable paradigm.

In $s$-wave superconductors with a small concentration of magnetic impurities, the only electronic excitations that remain available at low temperatures are the excitations of the system of localized spins. We discuss a mechanism of interaction between electromagnetic waves and the localized spins in disordered superconductors. A supercurrent induces randomly distributed spin density of the itinerant electrons, which couples to the impurity spins by exchange interaction. Acceleration of the Cooper pair condensate by the external $\text{ac}$ electric field of frequency $\omega$ creates a strong, time-dependent exchange field acting on the localized spins, which is inversely proportional to $\omega$. As a result, at low frequencies the dissipative conductivity saturates to a nonzero value. We also predict that, in the presence of a $\text{dc}$ magnetic field parallel to the superconducting film, the system exhibits a large positive magnetoconductance. Using the fluctuation-dissipation theorem, we evaluate the spectrum of equilibrium current fluctuations induced by the spin fluctuations.

Governed by the Nielsen-Ninomiya theorem, Weyl points (WPs) function as topological monopoles that cannot exist in isolation but must form charge-neutral assemblies in the momentum space of crystals. While these WPs are locally characterized by quantized chiral charges, the finite generating family governing their global assembly into a Weyl semimetal (WSM) phase remains undiscovered. Here, we resolve this by identifying “irreducible Weyl molecules” (IWMs) as the elementary, charge-neutral topological building blocks of WSMs. By rigorously imposing the constraints of 1651 magnetic space groups on minimal zero-sum chiral-charge sequences, we obtain exactly 16 crystallographically realizable IWMs. We establish a universal linear-combination principle, demonstrating that any crystallographically realizable charge-neutral chiral-node configuration $Y$ within $\left|C\right|\le 4$ is constructed from a linear superposition of these 16 generators $X_i$ with non-negative integer coefficients $n_i$, governed by $Y={\sum }_{i=1}^{16}{n}_i{X}_i$. Utilizing first-principles calculations on a predicted family of boron allotropes, we reveal that this superposition principle organizes the bulk nodal configurations and constrains the admissible end point connectivity of Fermi arcs, while the realized surface geometry remains dependent on termination, energy, and allowed inter-IWM reconstruction. Our work establishes a “periodic table” for WSMs, offering a general theoretical framework for the classification and rational design of Weyl complexes.

We develop the semiconductor Wannier equations (SWEs), a real-time, real-space formulation of ultrafast light-matter dynamics in crystals, by deriving the equations of motion for the electronic reduced density matrix in a localized Wannier basis. Working in real space removes the structure-gauge ambiguities that hinder reciprocal-space semiconductor Bloch equations. Electron-electron interactions are included at the time-dependent Hartree plus static screened-exchange level. Decoherence is modeled with three complementary channels: pure dephasing, population relaxation, and distance-dependent real-space dephasing, providing physically grounded damping for strong-field phenomena such as high-harmonic generation. Conceptually, the SWEs bridge real-space semiclassical intuition with many-body solid-state optics, offering a numerically robust and gauge-clean alternative to reciprocal-space approaches for nonlinear optical response and attosecond spectroscopy in solids.

We present a general framework for extracting conformal data from critical two-dimensional classical lattice models using finite-size tensor-network flow. The central idea is to identify, from transfer-matrix spectra, a self-consistent finite-size window together with a crossover scale that separates the finite-size-scaling regime from the finite-entanglement-scaling regime induced by bond-dimension truncation. Within this window, the central charge, scaling dimensions, and conformal spins can be estimated without requiring a unique critical fixed-point tensor or detailed prior knowledge of the underlying conformal field theory. We benchmark the framework using three tensor-network renormalization schemes for the critical two-dimensional Ising and three-state clock models. Across schemes, we find robust universal behavior below the crossover scale, enabling accurate extraction of conformal data up to relatively high conformal levels. The analysis also yields a natural operational definition of entanglement scaling for classical tensor-network calculations and, in turn, a complementary estimator of the central charge.