We present a unified framework for multipartite entanglement characterization based on the conditional gradient (CG) method, incorporating both fast heuristic detection and rigorous witness construction with numerical error control. Our method enables entanglement certification in quantum systems of up to ten qubits and applies to arbitrary entanglement structures. We demonstrate its power by closing the gap between entanglement and separability bounds in white-noise robustness benchmarks for a class of bound entangled states. Furthermore, the framework extends to entanglement robustness under general quantum noise channels, providing accurate thresholds in cases beyond the reach of previous algorithmic methods. These results position CG methods as a powerful tool for practical and scalable entanglement analysis in realistic experimental settings.

We give a closed-form construction of the $n$-qubit elegant joint measurement (EJM) that we proposed previously [Phys. Rev. Lett. 136, 190201 (2026)] and show that it is part of a tunable family of measurements with tetrahedrally arranged Bloch vectors. The construction is based on the interference pattern implied by a single-phase polynomial built from the elementary symmetric functions. It realizes a regular tetrahedral measurement for every $n$, and the corresponding measurement unitary lies at level $n+1$ of the Clifford hierarchy. Starting from this measurement, we ask whether the size of the local tetrahedron—and hence the single-qubit-versus-rest entanglement of the basis—can be varied while preserving its symmetry. For every even $n$ the answer is yes, and remarkably the size follows the same one-parameter law that governs the known two-qubit family, interpolating down to a 1-uniform basis. For $n=3$ the EJM is locally isolated, while for odd $n\ge 5$ we do not know an analogous closed-form family. We also give an analogous construction, valid for every $n\ge 3$, with square local geometry.

We propose a method for producing dense ensembles of cold neutral atoms without the use of magnetic fields. The method, which we call an opto-optical trap (OOT), is similar to the commonly used magneto-optical trap (MOT) but replaces the quadrupole magnetic field with additional laser beams that produce an equivalent effective magnetic field. We find through simulation that equivalent performance between the OOT and MOT is achieved for ${}^{174}\mathrm{Yb}$. We present a theoretical description of this method, followed by detailed simulations for the level structure of ${}^{174}\mathrm{Yb}$, and we discuss the unique advantages and challenges of this scheme for atom cooling and trapping. This method may enable a variety of ultracold-atom experiments that were previously limited by the presence of a MOT.

Preserving multipartite entanglement in open many-body quantum systems is fundamentally limited by unavoidable environmental noise. We study the open-system dynamics of multipartite entanglement in an anisotropic XXZ spin chain interacting with a thermal spin bath, focusing on two states with distinct types of multipartite entanglement: the generalized Greenberger-Horne-Zeilinger state and the generalized $W$ state. Using a master-equation approach combined with the Bethe ansatz technique, we show analytically that robustness of multipartite entanglement at low temperatures can be enhanced by suitably tuning the anisotropy of the system. Our results highlight interaction-induced spectral control as a mechanism for stabilizing multipartite entanglement in quantum computing platforms.

Measurement incompatibility and the negativity of quasiprobability distributions both demonstrate the signature of nonclassicality. However, their relations largely remained qualitative, and no explicit operational connection has been established. We provide an operational link between measurement incompatibility and the Margenau-Hill (MH) quasiprobability distribution associated with two dichotomic observables. We first derive the joint measurability (measurement compatibility) condition for any pair of dichotomic observables in arbitrary finite dimension $d$. We then rigorously prove that for any pair of unsharp dichotomic measurements in dimension $d$, the positivity of the MH distribution is equivalent to joint measurability, i.e., the MH distribution is positive if and only if the measurements are jointly measurable. We further introduce the MH-like quasiprobability distribution for $n$ dichotomic unsharp observables in arbitrary finite dimension and derive a sufficient condition of joint measurability when the observables are mutually anticommuting. Finally, we propose an interferometric setup, inspired by quantum-switch architectures, that directly reconstructs MH quasiprobability which in turn provides a test of incompatibility.

Quantum repeater networks distribute entanglement over lossy links while many users share a limited pool of entangled pairs. Most existing routing schemes either always use a single best path or rely on global optimizations that are hard to run in real time. Here we propose and analyze a simple alternative: a stochastic multipath rule in which each entanglement request is sent at random along one of several edge-disjoint repeater paths, with a single parameter that controls the bias between shorter and longer routes. Using a distance-dependent lossy network model with finite per-link capacities and probabilistic entanglement swapping, we develop an analytic description of the resulting end-to-end entanglement rate as a function of this bias and validate it with large-scale numerical simulations. We find that an intermediate bias consistently outperforms both deterministic extremes across distances, traffic patterns, attenuation, swapping noise, and congestion, bringing the rate close to simple capacity upper bounds and making link usage more even across networks. These results identify stochastic multipath routing as a simple classical-control strategy for improving entanglement distribution in near-term quantum repeater networks.

We experimentally show that an electric dipole moment of more than 1 Debye can be induced in the dysprosium (Dy) atom, in a long-lived state that is about $17513{\mathrm{cm}}^{-1}$ above the ground state. This metastable state is part of a strongly coupled opposite-parity doublet. Using optically detected microwave spectroscopy in an atomic beam, we determine the approximately $1.12{\mathrm{cm}}^{-1}$ doublet spacing for the five stable bosonic isotopes of Dy with kilohertz-level accuracy. From the shift of the microwave transition frequency in low electric fields (below 150 V/cm) and from optical spectra in high electric fields (up to 150 kV/cm), a reduced transition dipole moment of 7.65 $\pm$ 0.05 Debye between the doublet states is extracted. In high electric fields the doublet interacts with a third state at $17727{\mathrm{cm}}^{-1}$ that connects to the ground state via an electric-dipole transition. The three-state Stark interaction enables preparation of Dy atoms in the metastable state via single-photon excitation from the ground state. Our work experimentally validates predicted characteristics of the opposite-parity doublet and provides an effective route to the first doubly polar quantum gas of atoms.

We develop a general optimization framework for high-efficiency quantum cycles implemented with a trapped Bose-Einstein condensate, whose control parameters are the trap stiffness and the interaction strength, the latter tuned via Feshbach resonance. Combining a variational description of the condensate dynamics with Nelson's stochastic quantization, we map the quantum evolution onto an effective classical Ornstein-Uhlenbeck process, enabling the systematic optimization of each cycle stroke. The optimal protocol is obtained by minimizing a user-defined cost functional that selects the best trade-off between protocol duration and arbitrary physical constraints (such as the expended work or the proximity to an adiabatic evolution). The resulting protocols remain remarkably stable over repeated cycles, demonstrating the robustness of the optimization strategy. More generally, our framework provides a systematic route to the optimal control of nonlinear Schrödinger equations, with potential applications to quantum fluids, nonlinear optics, and quantum plasmas.

Vortex electrons, characterized by a helical phase front, offer unique advantages for probing material structures. Such electrons can be generated via tunneling ionization in strong laser fields. In this Letter, we investigate the rescattering dynamics of vortex photoelectrons by the parent ion. Specifically, we introduce vortex photoelectron holography, extending conventional strong-field photoelectron holography (SFPH) from plane-wave to vortex rescattering. By solving the time-dependent Schrödinger equation, we extract the vortex scattering phase from the SFPH fringes in the photoelectron momentum distribution. The result is in excellent agreement with scattering calculations, providing direct access to the vortex electron scattering phase. Our work establishes a basis for extending SFPH to molecular structure imaging with vortex photoelectrons.

We propose a general method to characterize classical stochastic noise causing qubit dephasing through repetitive Ramsey interferometry measurements (RIMs) on the qubit. Compared to filter-function-based spectroscopy, our method with simpler pulse control is less constrained by probe coherence time and can directly detect arbitrary-order correlation functions of quasistatic noise processes. We show that each RIM with a short evolution time and suitably chosen control pulses directly samples the noise field, and the $n$-point correlations of the RIM outcomes are proportional to the $n$-point correlation functions of the noise processes. We demonstrate the method numerically for two representative cases: an Ornstein-Uhlenbeck Gaussian process and a non-Gaussian ensemble of two-level fluctuators. While practical constraints such as readout contrast and sampling cost persist, our method offers a direct route to quasistatic classical noise spectroscopy across diverse platforms.

Radio-frequency dimer-projection spectroscopy has recently emerged as a powerful probe of strongly interacting Fermi gases, yet its frequency-resolved spectrum remains largely unexplored. Here we show that the spectrum exhibits two qualitatively distinct features: a broad quasiparticle continuum governed by fermionic pairing and a sharp pair-condensation peak arising from the coherent projection of condensed Cooper pairs onto the final-state dimer. To reveal this physics, we develop a point-dimer approximation that exploits the separation between the molecular and many-body length scales and expresses the radio-frequency response directly in terms of pair correlations in the initial many-body state. Within the BCS mean-field theory, we derive the frequency-dependent spectrum, identify the microscopic transfer processes underlying its structure, and show that the continuum possesses a threshold determined by the superfluid gap. Our theory establishes radio-frequency dimer-projection spectroscopy as a unified probe of short-range correlations, fermionic pairing, and long-range coherence in strongly interacting Fermi gases.

The non-Hermitian skin effect (NHSE) represents one of the most distinctive phenomena in non-Hermitian physics. Here, we uncover a new drag-induced NHSE mechanism in interacting Bose-Fermi mixtures where only bosons, but not fermions, experience asymmetric hopping. We show that strong Bose-Fermi interactions enable fermions to inherit boundary accumulation through correlated bound states. The interplay of interactions, quantum statistics, and non-Hermitian dynamics gives rise to an interaction-induced blockade mechanism, leading to highly asymmetric fermionic transport. We demonstrate that the drag-induced NHSE is dynamically stable and propose a feasible realization in ultracold Bose-Fermi mixtures with Floquet-engineered asymmetric tunneling. Our results establish a qualitatively distinct route to the NHSE, where non-Hermitian localization is not generated by direct nonreciprocal hopping of the localized particles themselves, but emerges through the interaction-mediated transfer of non-Hermitian dynamics between different quantum species. This mechanism further provides a potential route toward species-selective control of localization and transport in hybrid quantum matter.

In nonparaxial monochromatic light, the electric and magnetic fields generally have different energy densities, different singularities, and different polarization structures. This means that, whereas the nonparaxial topology of the electric and magnetic fields are individually well-studied, it is less obvious how to appreciate the relationship between the two fields and the way that this relationship varies over space. This requires understanding how nonparaxial light locally breaks fundamental symmetries (parity, duality, time-reversal) and offers a more complete picture of the topology of electromagnetic waves. With this work an electromagnetic ellipse that mixes electric and magnetic fields is introduced, residing not in real space, but in electric-magnetic (EM) space, whose geometry depends on such broken symmetries. The EM ellipse has circular and linear polarization singularities and may be organized into particlelike textures, even in common focused beams of light. Here, a second-order EM ellipse meron (a half skyrmion) is numerically demonstrated in a linearly polarized vortex beam.

Straight dark solitons in two-dimensional (2D) quantum fluids usually decay by transverse modulational instability, with no intrinsic suppression in contact-interacting Bose-Einstein condensates (BECs). We theoretically show that anisotropic long-range interactions in a quasi-2D dipolar BEC stabilize an embedded straight soliton, with spontaneous stripe order providing stronger pinning. The excitation spectra show that the lowest transverse solitonic branch remains gapped, while stripe-supersolid density modulation further hardens this branch and increases the soliton bending stiffness, penalizing transverse deformation. Accessible in current ${}^{166}\mathrm{Er}$ and ${}^{164}\mathrm{Dy}$ platforms, these results establish interaction-driven protection for straight dark solitons in structured quantum fluids.

We study synchronization in the XX qubit chain subject to local or multilocal amplitude-damping noise. We show that generic stable synchronization of the edge qubits occurs if and only if the decoherence-free subspace (DFS) supports exactly one single-excitation eigenstate. Analyzing the DFS structure of the model, we show that it is completely determined by a simple number-theoretic function involving the noise sites and the chain length. We further show that this same condition also guarantees constant asymptotic entanglement between the edge qubits, so that generic stable synchronization and constant asymptotic entanglement necessarily coexist. By contrast, when the DFS supports multiple single-excitation eigenstates, synchronization becomes initial state dependent and may be entirely absent, even though stable oscillatory entanglement can persist indefinitely. Our analysis can be extended to any excitation-conserving qubit chain mappable to free fermions and is directly testable on platforms with site-selective dissipation.

A single operational protocol based on free evolution and projective measurements yields inequivalent quantum time distributions through distinct postprocessing procedures. We construct an activity-based time-of-flow (TF) distribution and a presence-based quantum stroboscopic (QS) distribution, providing complementary operational notions of time. Applied to tunneling through a rectangular barrier, the regional QS mean saturates as the barrier width increases, whereas the TF mean first decreases and eventually grows for larger widths. These contrasting behaviors provide an operational interpretation of the Hartman effect, the apparent saturation of tunneling delay with increasing barrier width, in terms of quantum time distributions associated with flow through the exit region and occupation within the barrier, capturing the roles of early penetration, dominant reflection, and spectrally filtered transmission.

Neutral-atom arrays offer a promising path for quantum simulation, yet the potential of fermionic ${}^{40}\mathrm{K}$ remains largely constrained by state-dependent light shifts that degrade cooling and detection fidelities. This problem can be resolved by working at a magic wavelength, where the differential light shift vanishes. We report the first experimental determination of the magic wavelength for the $D_1$ transition in fermionic ${}^{40}\mathrm{K}$ at 1227.54(4) nm. Using in-trap loss spectroscopy in a wavelength-tunable optical tweezer, we map the differential ac Stark shift across a range of trapping powers and wavelengths. By converting these shifts to differential scalar polarizabilities, we find excellent agreement with relativistic all-order calculations. Benchmark measurements at 1064.49 nm further quantify the intensity-sampling systematics inherent to standard trapping wavelengths, contrasting with the “mechanically clean” environment provided by the magic condition. Our results provide an important step toward high-fidelity in-trap $D_1$ cooling, fluorescence imaging, and light-assisted loading, establishing a robust path toward scaling fermionic neutral-atom arrays for quantum information science.

Common belief, confirmed by existing experiments, is that arbitrarily weak disorder should lead to spatial localization of eigenmodes of scalar wave equations when wave propagation is two dimensional (2D). We predict that, contrary to this belief, a localization-delocalization transition can take place for light scattered by two-level atoms placed at random positions in the middle plane of a parallel-plate 2D waveguide fed by its fundamental transverse-magnetic mode (electric field polarized perpendicular to the waveguide and to the atomic plane). This transition, driven by near-field dipole-dipole interactions between atoms, occurs upon increasing the areal number density of atoms beyond some critical value. A finite-size scaling analysis of the transition yields an estimate of its critical exponent $\nu =1.4\pm 0.2$.