The temporal modulation of material parameters enables optical amplification within linear media. Here, we consider a subwavelength metal nanoparticle, the fundamental building block of plasmonics, and study how temporal modulation alters the optical response of these frequency-dispersive, time-varying, nanostructured media. We show that periodic temporal modulation gives rise to Floquet replicas of the localized surface plasmon resonance of the nanoparticle, which can result in light amplification. We propose a model based on a pointlike dipole description of the time-varying frequency-dispersive nanoparticle that fully captures the radiative and amplifying properties of the system in the subwavelength regime. By comparing our simplified model to full Floquet-Mie scattering calculations, we demonstrate that the optical scattering by the nanoparticle is accurately described by an analytical two-band model. This formulation allows us to introduce an effective two-frequency polarizability that fully incorporates the properties of the localized surface plasmon and its amplifying replica, as well as their interaction. In addition, we analyze the emergence of parametric amplification in the modulated nanoparticle, showing that amplification can be obtained in a broad range of parameters.

Plasmons are bosonic wavelike charge oscillations in solids and the plasmon group velocity ($v_{\mathrm{g}}$), the first derivative of momentum ($q$)-dependent dispersions, depicts the many-body electron motions of critical electronic importance. The profound characteristics of $v_{\mathrm{g}}$ in either three-dimensional (3D) or two-dimensional (2D) electron systems are nonetheless short of quantitative scrutiny. Using $q$-resolved electron energy loss spectroscopy, we tackle the $q$-dependent $v_{\mathrm{g}}$ of π and π + σ plasmons in 3D-bulk and 2D-monolayer (ML) $\mathrm{Mo}{\mathrm{S}}_2$ semiconductors, with the 2D $\mathrm{Mo}{\mathrm{S}}_2$ being the model transition-metal dichalcogenide (TMD) for emergent atomically thin electronics. $v_{\mathrm{g}}$ along with the underlining electronic parameters of the charge density, effective mass, and screening length in 2D for the plasmon dispersions is quantitatively elaborated. 2D $v_{\mathrm{g}}$ is further compared to those evaluated from metallic ML-TMD $\mathrm{Ta}{\mathrm{S}}_2$ and graphene, and the scaling over the single-particle Fermi velocity ($v_{\mathrm{F}}$) unveils a $v_{\mathrm{g}}/v_{\mathrm{F}}$ function generally obeyed by the semiconducting and metallic TMD and graphene of distinctly different massive and relativistic characters, respectively. Beyond the pertinent critical $q$ (on the order of ${10}^{-2}{\AA }^{-1}$) where one observes $v_{\mathrm{g}}=v_{\mathrm{F}}$, electric-field lines connecting the oscillating 2D charges would turn from vacuum into the atomically thin matters, concomitant with the increasing plasmon damping and reducing $v_{\mathrm{g}}$ ($v_{\mathrm{g}}<v_{\mathrm{F}}$). Long-wavelength 2D plasmons below the critical $q$ characterize the field lines largely in vacuum and are persistent and fast ($v_{\mathrm{g}}>v_{\mathrm{F}}$), with high-speed application merits. Conversely, 3D plasmons in bulk $\mathrm{Mo}{\mathrm{S}}_2$ never exceed $v_{\mathrm{F}}$.

We develop a non-Gaussian variational approach that enables us to study both equilibrium and far-from-equilibrium physics of the two-dimensional Fermi polaron. This method provides an unbiased analysis of the polaron-to-molecule phase transition without relying on truncations in the total number of particle-hole excitations. Our results—which include the ground-state energy and quasiparticle residue—are in qualitative agreement with the known Monte Carlo calculations. The main advantage of the non-Gaussian states compared to conventional numerical methods is that they enable us to explore long-time polaron evolution and, in particular, study various spectral properties accessible to both solid-state and ultracold atom experiments. We design two types of radiofrequency spectroscopies to measure polaronic and molecular spectral functions. Depending on the parameter regime, we find that these spectral functions and fermionic density profiles near the impurity either display long-lived oscillations between the repulsive and attractive polaron branches or exhibit fast relaxational dynamics to the molecular state.

We investigate the Nagaoka-Thouless ferromagnetic instability in the strongly interacting $t\text{−}{t}^{\prime }$ Hubbard model by continuously breaking particle-hole symmetry on a tunable square-triangular lattice geometry. We use an analytic approach to show that the fully spin-polarized state becomes unstable to a metastable spin polaron when the kinetic frustration $t^{\prime }/t$ exceeds a critical, dimension-dependent value. Large-scale density matrix renormalization group simulations reveal a quantum phase transition from the Nagaoka ferromagnet to a spiral spin-density wave, which evolves continuously into the Haerter-Shastry antiferromagnet in the large-frustration limit. Remarkably, this transition remains robust at low but finite hole density, making it accessible in cold-atom and moiré Hubbard platforms under strong interactions. A variational analysis further captures the instability mechanism at finite hole density via frustration-induced magnon band deformation.

We study the transport of active Brownian particles (ABPs) in three-dimensional (3D) spatially periodic oscillatory geometries. We establish a generalized Fick-Jacobs approach that reduces a 3D system to an effective one-dimensional (1D) system, assuming that particles quickly reach a steady state in the transverse directions of the geometry. The resulting 1D framework connects passive, static, and pulsating limits and provides robust predictions. The transport characteristics of ABPs are computed semianalytically and corroborated by numerical simulations. At the optimal frequency of the geometry oscillation, particles exhibit higher average velocity $\langle v\rangle$ and effective diffusion coefficient $D_{\text{eff}}$, resembling the phenomena of stochastic resonance. This effect is further enhanced by the self-propelled velocity of ABPs and the amplitude of geometry oscillations. These findings have significant implications for the development of micro- and nanofluidic devices with enhanced control over particle transport and precise manipulation of small-scale biomedical devices.

Friction is ubiquitous in daily life, from nanoscale machines to large engineering components. By probing the intricate interplay between system parameters and frictional behavior, scientists seek to unveil the underlying mechanisms that enable prediction and control of friction—an essential step toward carbon neutrality. Yet, reproducing frictional behavior in experiments is notoriously difficult. Here, we experimentally show that this challenge stems from the extreme sensitivity of tribological systems to tiny variations, e.g., in surface topography, typically presumed well controlled. Even after meticulous surface preparation to semiconductor industry standards and curtailing misalignment-induced oscillations, subtle variations remain and interact. In turn, such minute initial differences lead to statistically significant variations in friction and wear, giving rise to system-level chaotic behavior. Yet, by leveraging mid-scale features of surface topography and misalignment-induced oscillations—information often filtered out or overlooked—we established a predictive framework for high-friction regions under vastly different lubrication scenarios. While no single identified descriptor robustly predicts high friction, their combined occurrence provides strong predictive ability, which is further enhanced by machine learning.

We present a quantitative investigation of one- and two-body light-mediated processes that occur to few erbium atoms in an optical tweezer, when exposed to near-resonant light. In order to study the intertwined effects of recoil heating, cooling, and light-assisted collisions, we develop a first-principles Monte Carlo algorithm that solves the coupled dynamics of both the internal and external degrees of freedom of the atoms. After validating our theoretical model against experimental data, we use the predictive power of our code to guide our experiment and, in particular, we explore the performance of different transitions of erbium for light-assisted collisions in terms of their efficiency and fidelity for single-atom preparation.

Wigner's Friend-type paradoxes challenge the assumption that events are absolute—that when we measure a system, we obtain a single result, which is not relative to anything or anyone else. These paradoxes highlight the tension between quantum theory and our intuitions about reality being observer independent. Building on a recent result that developed these paradoxes into a no-go theorem, namely, the Local Friendliness theorem, we introduce the Causal Time-Symmetric Friendliness Paradox, a time-ordered analog of it. In this framework, we replace the usual locality assumption with Axiological Time Symmetry and show that, when combined with the assumptions of Absoluteness of Observed Events (AOE), No Retrocausality, and Screening via Pseudo Events, we obtain a Causal Time-Symmetric Friendliness inequality. We then show that quantum mechanics violates this inequality and is therefore incompatible with at least one of these assumptions. To probe which assumption might be incompatible, we then examine whether AOE in its entirety is essential for this no-go result. We propose a weaker, operational form of AOE that still leads to inequalities that quantum mechanics violates. This result shows that even under relaxed assumptions, quantum theory resists reconciliation with classical notions of absolute events, reinforcing the foundational significance of Wigner's Friend-type paradoxes in timelike scenarios.

Quantum gravity effects are expected to resolve the black hole singularity and the effects may deform the region near but outside the horizon. Applying AdS/CFT correspondence, we see their signatures from the viewpoint of dual conformal field theory. As a regularized geometry, we consider AdS gravastar constructed by gluing AdS-Schwarzschild and de Sitter spacetime. The retarded Green's functions of dual conformal field theory have bulk-cone singularities associated with null trajectories in the bulk and we obtain the singularities specific to a horizonless geometry. We also observe echoes coming from waves reflected behind the photon sphere. The existence of echoes implies the modification of geometry inside the photon sphere.

Topological phases in one-dimensional lattices are usually described by fixed, frequency-independent Hamiltonians, where topology is determined solely by structural parameters. However, in many wave-based systems with internal resonances, effective couplings become intrinsically dispersive and depend on the eigenfrequency itself. Here, we develop an analytical theory of such frequency-dependent topology using a trimer (SSH3) mass-spring lattice as a minimal model. By exactly eliminating the internal sublattice, the three-band SSH3 dynamics are mapped onto an effective two-sublattice Hamiltonian with frequency-dependent inertial and coupling terms. Because the effective parameters depend explicitly on the eigenfrequency, the resulting eigenvalue problem is nonlinear in $\omega$ and self-consistently reproduces the full three-band spectrum despite the two-level representation. This mapping reveals that the resonant effective coupling $G_2\left(\omega \right)$ acts as a bifurcation parameter controlling band inversion, redistribution of integer winding numbers, and the emergence of edge-localized modes. We show that a sign reversal of $G_2\left(\omega \right)$ induces a frequency-selective topological transition accompanied by a winding redistribution $({\nu }_1,{\nu }_2,{\nu }_3)=(-1,2,-1)$ and analytically predictable in-gap edge states governed by closed-form localization criteria. Within this framework, the bulk-edge correspondence is not determined by a fixed Hamiltonian but by the effective Hamiltonian evaluated self-consistently along the bulk dispersion relation. The formulation is further extended to adiabatically modulated lattices, where locally nontrivial Berry curvature and alternating topological charges emerge on the $(q,t)$ torus, while the global Chern number remains neutral. Because dispersive renormalization arising from internal degrees of freedom is ubiquitous in phononic, photonic, and other wave-based lattice systems, the present theory establishes a general analytical framework for topological phases in dispersive multisublattice media beyond conventional static tight-binding descriptions.

Active optical clocks based on collective atomic emission promise narrow lasing linewidths as well as reduced sensitivity to cavity fluctuations, yet residual frequency pulling limits their ultimate precision. Here, we propose a laser scheme that simultaneously achieves vanishing frequency pulling and ultranarrow linewidths by exploiting symmetry in collective superradiant emission. Atoms in a dense beam traversing a bad cavity are prepared in controlled superposition states using a pump laser with a sinusoidally modulated Rabi frequency ${\mathrm{\Omega }}_{\mathrm{m}}$. The resulting emission spectrum consists of a central lasing peak at the atomic resonance and two superradiant sidebands at symmetric detunings $\pm {\mathrm{\Omega }}_{\mathrm{m}}$. Owing to their symmetric interaction, the central peak is protected against cavity-induced frequency shifts over detunings comparable to the cavity linewidth. As the atom number increases, its linewidth narrows far beyond the conventional gain-narrowing limit, reaching values as small as one millionth of the cavity linewidth. Small pump detunings break the symmetry of the sideband intensities, providing a robust error signal to stabilize the pump frequency without an external reference cavity. These results establish a symmetry-driven route toward ultrastable active optical clocks and collective-radiation sources with exceptional frequency stability.

Encoding classical data in a quantum state is a key prerequisite of many quantum algorithms. Recently, matrix product state (MPS) methods emerged as the most promising approach for constructing shallow quantum circuits approximating input functions, including probability distributions, with only linear number of gates. We derive rigorous asymptotic expansions for the decay of entanglement across bonds in the MPS representation depending on the smoothness of the input function, real or complex. We also consider the dependence of the entanglement on localization properties and function support. Based on these analytical results, we construct an improved MPS-based algorithm yielding shallow and accurate encoding quantum circuits. By using tensor cross interpolation, we are able to construct utility-scale quantum circuits in a compute- and memory-efficient way. We validate our methods by loading heavy-tailed distributions, including Lévy, important in finance, but they apply to any smooth function inputs. We test the performance of the resulting quantum circuits by executing and sampling from them on IBM quantum devices, for up to 156 qubits.

Interfaces between topological insulators and superconductors (SCs) are promising platforms for realizing Majorana zero modes (MZMs) via the superconducting proximity effect. We introduce a bilayer model consisting of the surface states of a three-dimensional topological insulator (3DTI) coupled to an $s$-wave superconductor and systematically study the role of interlayer tunneling strength ($t_{\perp }$) motivated by the recent growth of the $\mathrm{Fe}\left(\mathrm{Te},\mathrm{Se}\right)/{\mathrm{Bi}}_2{\mathrm{Te}}_3$ heterostructure. We find that increasing $t_{\perp }$ shifts the proximity-induced (PrI) gap minimum away from the $\mathrm{\Gamma }$ point, giving rise to momentum-selective interference patterns that manifest as spatial oscillations in the in-gap states. We introduce an antidot with a magnetic vortex in the model and investigate the resulting in-gap states, including MZMs and Caroli–de Gennes–Matricon (CdGM) modes. With increasing hybridization strength, the energy separation between MZMs and CdGM states increases, enhancing the isolation of MZMs. Importantly, in the strong hybridization limit, the leading CdGM separation remains large in spite of the decrease in the PrI gap. Spin- and spatially resolved wavefunction analysis reveals angular momentum asymmetries absent in conventional $s$-wave systems. A direct comparison with a standalone $s$-wave superconductor confirms the emergence of distinct $p$-wave-like features in the bilayer geometry. Our results provide experimentally relevant predictions for tuning the stability of MZMs and their differentiation from the CdGM modes in SC-3DTI heterostructures and offer a theoretical framework for probing unconventional superconductivity in engineered topological systems.

Theoretical and computational studies predict topological charge separation at active-passive interfaces in active nematics, but reliable experimental validation has been lacking. We utilize a synthetic acoustically energized liquid crystal to experimentally investigate the dynamics of topological defects across an active-passive interface. The interference pattern induced by the acoustic wave inside the experimental cell creates a spatial distribution of activity, resulting in the formation of active-passive interfaces with the liquid-crystalline director field aligned parallel to those interfaces. The activity gradient drives the reorientation of positively charged topological defects along its direction, causing them to migrate into the passive zone and form a layer with net topological charge. That layer “discharges” upon cessation of activity through annihilation of positive and negative topological charges, resembling the discharge of a capacitor.

The quantum error correction threshold is closely related to the Nishimori physics of random statistical models. We extend quantum information measures such as coherent information beyond the Nishimori line and establish them as sharp indicators of phase transitions over the full $p\text{−}T$ plane. These generalized measures admit a natural operational interpretation as diagnostics of inference mismatch for decoders operating at an effective temperature. We derive exact inequalities for several generalized measures, demonstrating that each attains its extremum along the Nishimori line. As a direct application, we study these measures in the 2d $\pm J$ random-bond Ising model—corresponding to a surface code under bit-flip noise—and revisit the Nishimori multicritical point. Among all indicators, coherent information exhibits the weakest finite-size effects, enabling a high-precision estimate $p_c=0.1092212\left(4\right)$ and the associated critical exponents.

Understanding how spin-orbit coupling shapes ultrafast electron dynamics remains a central challenge across atomic, molecular, and condensed-matter systems. Here, we demonstrate that spin-orbit splitting in krypton naturally separates two distinct regimes of attosecond interferometry: a conventional above-threshold process involving interference between continuum pathways and an under-threshold regime in which discrete and continuum intermediate states coexist and interfere. Using spin-orbit and angle-resolved measurements with attosecond precision, supported by ab initio time-dependent simulations, we reveal that the under-threshold channel exhibits dramatic phase and delay variations—up to several hundred attoseconds—highly sensitive to photon energy and emission direction. In contrast, the conventional above-threshold channel shows smooth, featureless behavior. This duality exposes the strong influence of metastable resonances, establishing spin-orbit splitting as a built-in control knob for accessing structured continua. Beyond krypton, our results provide a broadly applicable framework for probing and controlling coupled spin, orbital, and many-body correlation dynamics at the attosecond timescale.

We introduce an active-space embedding framework for core-level spectroscopies that connects localized atomic multiplets to continuum resonances within a plane-wave density functional theory/projector augmented-wave description. The approach is complementary to widely used core-level Bethe-Salpeter implementations based on a two-particle (core-exciton) picture with typically static screening: Here, a correlated multiplet manifold of the absorber (including the core hole and open-shell configurations) is coherently coupled to a plane-wave photoelectron, enabling a unified treatment of localized multiplet structure and continuum lineshapes. Spectra are computed in a general time-domain formulation equivalent to Fermi's golden rule: A transition operator tailored to the specific spectroscopy technique is applied to the correlated ground state to generate an excited wave packet, and the corresponding wave packet autocorrelation function is evaluated without explicit real-time propagation, using Lanczos tridiagonalization or the kernel polynomial method; the spectral intensity follows from its Fourier representation. We validate the method at the Ce $N_{4,5}$ edges, reproducing in quantitative agreement with experiment both high-$Q$ multiplet features and the low-$Q$ giant dipole resonance continuum, including a characteristic low-energy shoulder relevant for robust Ce valence assignments. The implementation is available open source within the quantum espresso xspectra package (xspectruplet mode), together with reproducible inputs and scripts.