We demonstrate an experimental approach to determine magneto-optical effects that combines x-ray magnetic circular dichroism (XMCD) with x-ray interferometry, based on the concepts of Young's canonical double slit. By covering one of two slits with a magnetic thin film and employing XMCD, we show that it is possible to determine both the real and the imaginary parts of the complex refractive index by measuring the fringe shifts that occur due to a change in the sample magnetization. Our hybrid spectroscopic-interferometric methodology provides a means to probe changes in the magnetic refractive index in terms of the electron spin moment.

Solving the many-electron problem, even approximately, is one of the most challenging and simultaneously most important problems in contemporary condensed matter physics with various connections to other fields. The standard approach is to follow a divide and conquer strategy that combines various numerical and analytical techniques. A crucial step in this strategy is the derivation of an effective model for a subset of degrees of freedom by a procedure called downfolding, which often corresponds to integrating out energy scales far away from the Fermi level. In this work, we present a rigorous formulation of this downfolding procedure, which complements the renormalization group picture put forward by Honerkamp [Phys. Rev. B 85, 195129 (2012)]. We derive an exact effective model in an arbitrarily chosen target space (e.g., low-energy degrees of freedom) by explicitly integrating out the rest space (e.g., high-energy degrees of freedom). Within this formalism, we state conditions that justify a perturbative truncation of the downfolded effective interactions to just a few low-order terms. Furthermore, we utilize the exact formalism to formally derive the widely used constrained random phase approximation, uncovering underlying approximations and highlighting relevant corrections in the process. Finally, we detail different contributions in the material examples of fcc nickel and the infinite-layer cuprate ${\mathrm{SrCuO}}_2$. Our results open up a pathway to obtain effective models in a controlled fashion and to judge whether a chosen target space is suitable.

We analyze a system of dipolar atoms confined in geometries of quasi low dimensionality. Due to the long-range and anisotropic nature of dipolar interactions, the system supports both stable solitons and quantum droplets. In quasi-one-dimensional geometries, the transition between these states is known to manifest either as a first-order phase transition, associated with bistability, or as a smooth crossover. We investigate this transition by calculating the structure factor and showing that the response of the breathing mode provides an experimentally accessible probe. In addition, we identify regions of both bistability and smooth crossover in quasi-two-dimensional geometries. Finally, we connect our findings to previous experimental results and delineate the conditions under which two-dimensional dipolar bright solitons can be realized.

Understanding the response of diamond abrasive grains to mechanical loading remains crucial for optimizing their performance in precision manufacturing. In that context, the role of the initial residual stress and crystallographic orientation of the grains is poorly understood. We investigate synthetic diamond grains in two different grit sizes (D126, D252) subjected to directional loading up to 100 N using x-ray diffraction and spatially resolved Raman spectroscopy. Small grains with preferential (111) orientation show an unexpected stress evolution under contact pressures up to 16 GPa, with Raman shifts increasing from 1331.3 to $1333.0{\mathrm{cm}}^{-1}$, indicating an enhanced local compressive stress state at the probed surface regions. Conversely, large (311)-oriented grains exhibit a heterogeneous stress development with Raman shifts varying from 1331.5 to $1332.6{\mathrm{cm}}^{-1}$, including regions that become more tensile (or less compressive) relative to their initial state. The relationship between the relative Raman shift and a spatially weighted contact pressure follows an empirical power law $\delta E\propto p_{\text{c}}^{\prime \alpha }$ with opposite, orientation-dependent exponents: $\alpha \approx +0.25$ for (111) grains showing progressive compression enhancement and $\alpha \approx -0.35$ for (311) grains exhibiting a trend toward tensile stress components with increasing load. Molecular dynamics simulations reveal that the Schmid factor governs this orientation-dependent response: The low Schmid factor (0.27) for [111] loading restricts dislocation glide, leading to stress retention with high elastic recovery, while the high Schmid factor (0.45) for [311] loading facilitates plastic flow and stress relaxation despite lower peak stress. These findings demonstrate that stress evolution in diamond under directional loading is controlled by the geometric relationship between loading direction and slip systems, providing mechanistic insights for diamond tool design.

We present a comprehensive first-principles investigation of carbon self-interstitial defects in diamond, ranging from mono- to hexa-interstitial complexes. By density functional theory, empowered by interatomic potential models, we efficiently sample the complex configurational landscape and identify both known and previously unreported defect geometries. Our results reveal a pronounced energetic driving force for aggregation: The formation energy per interstitial decreases systematically from isolated split interstitials to compact multi-interstitial clusters, with the tetra-interstitial platelet emerging as a particularly stable structural motif. Additionally, charge analysis indicates that the predominantly covalent bonding in diamond becomes more polar within the defect centers. Analysis of defect energy levels shows that only the investigated mono-, di-, penta-, and hexa-interstitial complexes introduce in-gap electronic states, whereas the tri- and tetra-interstitial clusters are electronically inert. Vibrational spectroscopies further reveal that self-interstitials generate characteristic signatures. Short carbon-carbon bonds inside the defect cores give rise to high-frequency vibrational modes between 1375 and ${1925\mathrm{cm}}^{-1}$, which are strongly infrared active but exhibit weak Raman activity. Through a systematic analysis of metastable configurations, we identify the 3H defect center as a neutral di-interstitial defect. Based on this identification, we further suggest that the TR12 center may arise from a 3H-containing defect like a metastable hexa-interstitial configuration. Taken together, these findings provide a coherent picture of the structural, electronic, and vibrational characteristics of carbon self-interstitials and establish a robust framework for their experimental identification.

The ability to tune interparticle interactions is one of the main advantages of using ultracold quantum gases for quantum simulation of many-body physics. Current experiments with ultracold polar molecules employ shielding with microwave or static electric fields to prevent destructive collisional losses. The interaction potential of microwave-shielded molecules can be tuned by using microwaves of two different polarizations, while for static-field-shielded molecules the tunability of interactions is more limited and depends on the particular species. In this work, we propose a general method to tune the interactions between static-field-shielded molecules by applying a microwave field. We carry out coupled-channel scattering calculations in a field-dressed basis set to determine loss rate coefficients and scattering lengths. We find that both the s-wave scattering length and the dipole length can be widely tuned by changing the parameters of the microwave field, while maintaining strong suppression of lossy collisions.

The dead zones of atomic magnetometers bring great challenges for the mobile applications in high-sensitivity magnetic field measurement. To solve this fundamental problem, we present a dead-zone-free orientation-based atomic magnetometer employing free-induction-decay (FID) scheme. A modulation scheme combining synchronous optical pumping and radio frequency pulse manipulation is utilized to achieve the free precession of spin polarization in all magnetic field orientations, and the FID signals are detected in two directions with an orthogonal pump-probe light configuration. We perform a comprehensive theoretical analysis of spin polarization evolution for arbitrary magnetic field orientations, and both simulation and experimental results demonstrate that the fusion of information from the pump and probe beams enables the dead-zone-free measurement of the magnetometer, with the sensor exhibiting a sensitivity in the range of $0.6–1.4\mathrm{pT}/{\mathrm{Hz}}^{1/2}$ across all directions. The proposed scheme is of great significance for the advancement of pulsed atomic magnetometers and their various applications in mobile platforms.

Adaptive control in biological systems, such as intestinal immunity, remains poorly understood despite detailed knowledge of underlying regulatory networks. We propose an alternative framework based on stochastic martingale turnover, in which cells proliferate through mutual competition and decay without cell-type-specific regulation. Through stochastic simulations and mathematical analysis, we show that this process autonomously generates balanced population compositions associated with low-decay probabilities. The compositional dynamics can be described as a random walk whose step lengths decrease in low-decay regions. Reduced decay leads to larger total population sizes and an increase in the number of compatible microscopic states, which in turn shapes the distribution of compositions under fluctuating conditions. More generally, the dynamics follow a modified Langevin equation, in which constant mass is replaced by a fitness-dependent effective mass proportional to the total population size. Thus, biological systems regulate resistance to change, not merely direction, in shaping their macroscopic behavior.

Quantum information scrambling (QIS) describes the rapid spread of initially localized information across an entire quantum many-body system through entanglement generation. Once scrambled, the original local information becomes encoded globally, inaccessible from any single subsystem. In this work, we introduce a circuit-based decoding protocol. By utilizing the concept of postselected closed timelike curves (PCTCs), we demonstrate how postselection allows us to interpret an ordinary quantum experiment as an example of a paradox-free trajectory, simulating a consistent time loop and reliable information recovery. Specifically, when conditioned on a final postselected outcome, this experiment can be interpreted as decoding the scrambled information even before the original information is generated. Furthermore, the success probability of the PCTC is governed by out-of-time-ordered correlations, which is a standard measure of QIS. We experimentally implement our protocol on cloud-based Quantinuum and IBM quantum processors. Our approach illuminates a unique quantum task under postselection: the causally consistent simulation of future-to-past scrambled information retrieval.

In this work, we propose performing key operations in quantum computation and communication using room-temperature atoms moving across a grid of high-quality-factor, small-mode-volume cavities. These cavities enable high-cooperativity interactions with single atoms to be achieved with a characteristic timescale much shorter than the atomic transit time, allowing multiple coherent operations to take place. We study scenarios where we can drive a Raman transition to generate photons with specific temporal shapes and to absorb, and hence detect, single photons. The strong atom-cavity interaction can also be used to implement the atom-photon controlled-phase gate, which can then be used to construct photon-photon gates, create photonic cluster states, and perform nondemolition detection of single photons. We provide numerics validating our methods and discuss the implications of our results for several applications.

The electromagnetic response of matter is governed by three fundamental multipole families: electric, magnetic, and toroidal. While the electric and magnetic are cornerstones of physics, the toroidal dipole (TD) has eluded direct, quantitative measurement for over 60 yr. Its far-field signature is masked by the electric dipole, and its behavior in the quantum regime remains largely unexplored. We address this long-standing problem by presenting a complete quantum-mechanical formalism for the TD in a nanostructure and proposing a spectroscopic method for its direct measurement. Focusing on a particle confined to a toroidal manifold—a geometry physically realized in systems such as carbon nanotube tori and topological insulator nanorings—we analyze the spectral response to an external toroidal current. We demonstrate that the resulting Aharonov-Bohm-like energy shifts are directly proportional to the expectation value of the TD operator. The transition energies exhibit a linear dependence on this current, with a quantized slope that directly reveals the change in the TD quantum number between eigenstates. This provides a clear experimental blueprint to unveil, measure, and characterize this elusive third multipole moment and its quantum nature, opening avenues in quantum metamaterials, nanoscience, and the study of fundamental symmetries.

Propagation of intense laser pulses in underdense plasma always involves nonlinear evolution of the laser envelope, which leads to large deviations from the initial Gaussian intensity profile. The modulations in the intensity envelope have strong influence not only on the formation of the wakefield, but also in the process of electron injection; thus, it defines the final spectral and angular distribution of the accelerated electrons. Better understanding of the laser pulse evolution is crucial for the correct interpretation of the experimental results, especially in the highly relativistic regime. We developed a simple numerical tool, which adequately models the evolution of the laser envelope up to the point when the spectral broadening becomes significant. Our numerical modeling sheds light on the asymmetric wakefield generation and consequent off-axis injection of electrons, observed in experiments and particle-in-cell simulations.

The intermediate valence of Ce in ${\mathrm{CeCo}}_5$ challenges standard density functional theory (DFT) and static $\mathrm{DFT}+U$ approaches, which fail to capture its magnetic properties. By combining $\mathrm{DFT}+U$ with exact diagonalization of the Anderson impurity model for the Ce $4f$ shell, we find a substantial reduction of Ce spin and orbital moments, consistent with $\mathrm{DFT}+\mathrm{DMFT}$ (dynamical mean-field theory), arising from ${\mathrm{Ce}}^{4+}-{\mathrm{Ce}}^{3+}$ valence fluctuations. The total magnetic moment of 6.70 ${\mu }_B$ agrees with experiment, and the calculated $4f$ density of states reproduces photoemission and bremsstrahlung isochromat spectra. The uniaxial magnetic anisotropy energy reaches 4.8 meV/f.u. when Coulomb correlations on both Ce $4f$ and Co $3d$ shells are included, in very good agreement with experimental data. These results highlight the importance of dynamical correlations and provide guidance for exploring high-performance, low-rare-earth-content permanent magnets.

Geometric phases play an enormous role in optics and are generally associated with the evolution of light's polarization state on the Poincaré sphere, or its spin on the sphere of spin directions. Here, we put forward an optical geometric phase that appears exclusively in nonparaxial light, resulting from cyclic changes to the relative amplitude and phase between the electric and magnetic fields. This phase is naturally represented on a recently introduced “electric-magnetic” sphere.

We introduce a plasma wakefield acceleration scheme capable of boosting initially subrelativistic particles to relativistic velocities within millimeter-scale distances. A subluminal light pulse drives a wake whose velocity is continuously matched to the beam speed through a tailored plasma density, thereby extending the dephasing length. We develop a theoretical model that is generalizable across particle mass, initial velocity, and the particular accelerating bucket being used, and we verify its accuracy with particle-in-cell simulations using laser drivers with energies in the joule range.

We introduce a quasiclassical Green's function approach describing the unitary yet irreversible dynamics of quantum systems effectively acting as their own environment. Combining a variety of concepts of quantum many-body theory, notably the nonlinear $\sigma$ model of disordered systems, the $G\mathrm{\Sigma }$ formalism for strong correlations, and real-time path integration, the theory is capable of describing a wide range of system classes and disorder models. It extends previous work beyond perturbation theory (in inverse Hilbert-space dimensions), enabling a description of thermalization dynamics from short scattering times, through the onset of ergodicity at an effective “Thouless time,” up to the many-body Heisenberg time. We illustrate the approach with two case studies: (1) a brickwork model of unitarily coupled quantum circuits with and without conserved symmetries and (2) an array of capacitively coupled quantum dots. Using the spectral form factor as a test observable, we find good agreement with numerical simulations. We present our formalism in a self-contained and pedagogical manner, aiming to provide a transferable toolbox for the first-principles description of many-body chaotic quantum systems in regimes of strong entanglement.

In non-Markovian systems, the current state of the system depends on the full or partial history of its past evolution. Owing to these time correlations, non-Markovian noise violates common assumptions in gate characterization protocols such as randomized benchmarking and gate-set tomography. Here, we perform a case study of the effects of a quantum non-Markovian bath on qubit randomized benchmarking experiments. We consider a model consisting of qubits coupled to a multimode bosonic bath. We apply unitary operations on the qubits, interspersed with brief interactions with the environment governed by a Hamiltonian. Allowing for non-Markovianity in the interactions leads to clear differences in the randomized benchmarking decay curves in this model, which we analyze in detail. The Markovian model’s decay is exponential as expected, whereas the model with non-Markovian interactions displays a much slower, almost polynomial, decay. We develop efficient numerical methods for this problem that we use to support our theoretical results. These results inform efforts on incorporating quantum non-Markovian noise in the characterization and benchmarking of quantum devices.

We show that a single non-Hermitian defect embedded in an otherwise Hermitian topological lattice can anomalously relocate an edge state into the bulk without altering the topology. Using one- and two-dimensional models, including the Su-Schrieffer-Heeger chain and honeycomb lattices, we demonstrate that tuning an asymmetric coupling or a local parity-time-symmetric perturbation shifts the edge mode to the defect site, where it becomes strongly localized. In two dimensions, the defect further acts as a momentum-bandpass filter, selectively relocating a narrow subset of edge modes from the continuum of boundary states. This relocation is distinct from the non-Hermitian skin effect, which drives collective bulk accumulation, and from trivial defect-induced modes, which lack topological origin. The effect is robust against disorder and system size, enabling programmable, on-demand positioning of topological states for applications in photonic routing, switching, and robust sensing.