We study single-photon ionization of aligned ${\mathrm{H}}_2^{+}$ in low-intensity near-circular laser fields with lower photon energy numerically and analytically. The photoelectron momentum distribution (PMD) within the laser polarization plane, obtained by numerical simulations, shows a remarkable offset angle, which changes with changing the internuclear distance and the laser frequency. This phenomenon is different from that observed in recent experiments [Science 370, 339 (2020)], which is related to the PMD along the propagation direction of the laser. This phenomenon holds even for ${\mathrm{H}}_2^{+}$ with short-range Coulomb potentials but disappears for atoms, different from that observed in attoclock experiments. We show that the molecular Coulomb potential near the two atomic centers plays an important role here, and theoretical models associated with a more accurate continuum wave function of the molecule are needed for reproducing this phenomenon. This phenomenon also appears for other molecules such as ${\mathrm{N}}_2$. It can be useful for ultrafast probing of molecules with a high resolution of several attoseconds or even zeptoseconds.

We describe a novel type of interaction between open-shell polar molecules at sub-millikelvin temperatures. This hyperfine van der Waals interaction occurs between two molecules in two rotational states that differ by one quantum. Normally, this induces resonant dipolar interactions that lead to rapid collisional loss. For specific hyperfine states, however, selection rules prevent this. One can effectively turn off the dipolar interaction by merely flipping a nuclear spin. The resulting van der Waals interaction can be repulsive and can suppress collisional loss. We focus on laser-coolable CaF, but show this effect occurs universally for open-shell molecules, including MgF, SrF, BaF and YO. We propose that this effect could be measured by merging molecules in optical tweezers, where flipping a spin in one of the tweezers enables tuning of collision rates by five orders of magnitude.

In recent years, high harmonic generation (HHG) from topological matter has attracted considerable interest, emerging as a promising tool for detecting the topological phase. This work incorporates dephasing effects in the theoretical simulations of HHG from topological insulators described by finite-size tight-binding models. This is done by formulating a density-matrix approach in both length and velocity gauges within dipole approximation, with a gauge-invariant treatment of dephasing properly introduced such that the HHG response of a sufficiently large solidlike system is consistent with the periodic limit obtained using semiconductor Bloch equations. Applying the approach to Su-Schrieffer-Heeger chains reveals how dephasing affects the impact of topological edge states on the HHG spectra. It is found that dephasing can either weaken or strengthen the spectral contrast between the topological and trivial phases, depending on which of the intra- and interband mechanisms is dominant for a specific harmonic in the trivial phase.

We extend the quench spectroscopy method to dissipative and isolated non-Hermitian quantum lattice models via the case study of the open Bose-Hubbard chain and the non-Hermitian transverse-field Ising chain, respectively. We first investigate theoretically the dynamics of the open Bose-Hubbard chain confined in the superfluid phase induced by a sudden global quench on the dissipations and the repulsive interactions using the equation-of-motion approach. Using the same analytical approach, we then discuss the applicability of the quench spectroscopy to non-Hermitian quantum lattice models by considering the sudden global quench dynamics of the non-Hermitian transverse-field Ising chain confined in the paramagnetic phase. We finally generalize this spectroscopy method to isolated Hermitian quantum lattice models characterized by a quadratic fermionic or bosonic Hamiltonian. For this purpose, we consider the case study of the Hermitian version of the latter one-dimensional lattice model. The investigation is performed analytically for the bosonic and fermionic reformulations while considering for each case the equation-of-motion and quasiparticle theoretical approaches.

We propose a theoretical framework for engineering wave-vector angles in nonlocal nonlinear Floquet lattices to modulate photonic spin-orbit coupling (SOC). By controlling polar and azimuthal angles of transverse wave vectors in orthogonally polarized beams, we achieve tunable SOC strength, which governs the formation and propagation dynamics of topological edge states. The nonlocal nonlinearity introduces a distinct threshold for edge state emergence while enhancing their scattering robustness. The helical lattice geometry enables dual-parameter control, linking edge state velocity and topological band-gap adjustment through a single structural parameter. This system provides a platform for investigating nonlinear topological phenomena, with potential applications in on-chip photonic devices and quantum information processing.

We study the radiative dynamics of coupled electric dipoles, modelled as Lorentz oscillators, in the presence of real-time mechanical oscillations. The dipoles are treated in a self-consistent way through a direct electromagnetic simulation approach that fully includes the dynamical movement of the charges, accounting for radiation reaction, emission and absorption. This allows for a powerful numerical solution of optomechanical resonances without any perturbative approximations for the mechanical motion. The scaled population (excitation) dynamics of the Lorentz oscillators are investigated as well as the emitted radiation and electromagnetic spectra, which demonstrates how the usual dipole-dipole resonances couple to the underlying Floquet states, yielding multiple spectral peaks that are separated from the superradiant and subradiant states by an integer number of the mechanical oscillation frequency. Moreover, we observe that when the mechanical amplitude and frequency are sufficiently large, these additional spectral peaks undergo further modification, including spectral splitting, spectral squeezing, or shifting. These observations are fully corroborated by a theoretical Floquet analysis conducted on two coupled harmonic oscillators.

In this work, we theoretically analyze the population and entanglement dynamics for two identical qubits interacting with a graphene nanodisk. We consider qubits with various free-space decay rates in order to study how the coupling strength influences the dynamics of our composite system, as well as their entanglement evolution as quantified by concurrence. We find that for relatively large free-space decay rates, the population dynamics of each qubit features Rabi oscillations, while for smaller decay rates it exhibits a complex behavior, which nevertheless can be understood by semianalytical expressions using the sub- and superradiant states of the system. Additionally, we observe phenomena, such as population and entanglement trapping, induced by the strong interaction of the qubits with the graphene nanodisk, with trapping values depending solely on the initial conditions of the two qubits. Lastly, we compare our results with those obtained in the case of the two qubits interacting independently with a graphene nanodisk.

The momentum of light in dielectric media has been a century-long controversy that continues to attract significant interest. In a linear dielectric medium with refractive index $n$, the momentum is predicted to be smaller by a factor of $n$ according to Abraham and larger by the same factor according to Minkowski. By studying the coupled dynamics of electromagnetic waves and dipoles in a dielectric medium, we show that the change in momentum of the dipole, expressed by the Lorentz force, corresponds to the Abraham momentum and is given by the expectation value of the spin-projected momentum vector. On the other hand, the Minkowski momentum is obtained as the magnitude of the spin-projected momentum vector from the energy-momentum dispersion relation derived by diagonalizing the coupled Hamiltonian and determines the direction of refraction in accordance with Snell's law. Our model also predicts a zitterbewegung-like oscillation due to helicity mixing between left- and right-handed wave components, mediated by dipole oscillation. These internal wave dynamics may be observable via wave-packet motion or polarization-sensitive measurements.

Quantum optics routinely uses beam splitters to generate entanglement, including in pioneering experiments conducted by Hanbury-Brown and Twiss and Hong, Ou, and Mandel. The quantum interference at beam splitters lies at the heart of what makes boson sampling hard to emulate by classical computers and is a vital component of quantum computation with light. Yet, despite overwhelming positive evidence, the conjecture that beam splitters with equal reflection and transmission probabilities generate the most entanglement for any state interfered with the vacuum has remained unproven for almost two decades [Asbóth et al., Phys. Rev. Lett. 94, 173602 (2005)]. We prove this conjecture for ubiquitous entanglement monotones including mixed-state generalizations of entanglement entropy and purity by uncovering monotonicity and convexity with respect to photon loss for these monotones. At the same time, we highlight an infinite class of lesser-used monotones for which the conjecture fails. Because beam splitters are so fundamental, our results yield numerous corollaries for quantum optics, including proof of a recent conjecture for the evolution of a measure of quantumness through loss and a more efficient computational strategy for optimizing entanglement generation over linear optics. These results justify the value of seeking mathematical rigor behind commonly accepted facts and the danger of trusting them unconditionally.

In addition to the traditional two-level system, the three-level system serves as another important elemental building block for the manipulation of qubits. However, the quantum information processing in the three-level system is also subject to the decoherence induced by the interaction between the quantum system and its environment or by the crosstalk between different qutrits. In this work, we construct a sequence of physically feasible dynamical decoupling operators for the three-level system to mitigate not only the transverse dephasing between the excited state and ground states, but also the longitudinal relaxation among them. Combining the Hamiltonian engineering and our constructed dynamical decoupling sequence, we further realize the dynamical decoupling protection of qutrit-based quantum gates. Our scheme can effectively enhance the fidelity of three-level-based quantum gates through filtering out the environmental noises, which may provide a new horizon to improve the accuracy of three-level-based quantum manipulation.

We report measurements of the Landé $g$ factors for the $5d6s{}^3{D}_2$ hyperfine levels of ${}^{176}\mathrm{Lu}^{+}$ to a fractional inaccuracy of $5\times {10}^{-7}$. Combining these measurements with theoretical calculations allows us to estimate hyperfine-mediated modifications to the quadrupole moments for each state and infer a value of $\delta \mathrm{\Theta }=1.59\left(34\right)\times {10}^{-4}e{a}_0^2$ for the residual quadrupole moment of the ${}^1{S}_0\leftrightarrow {}^3{D}_2$ hyperfine-averaged clock transition.

While the adiabatic exchange of Majorana zero modes (MZMs) enables a nonuniversal set of geometrically protected gates, realizing an experimental implementation of MZM braiding remains challenging. In an alternative proposal, charge-parity measurement of two neighboring MZMs supports braiding by teleportation. Moreover, owing to the lack of definitive evidence of MZMs in semiconducting systems, there have been several simulations of MZMs on noisy intermediate-scale quantum devices which more naturally lend themselves to braiding. In this work, measurement-based braiding about MZM Y junctions is simulated by multiqubit parity measurements of a logical qubit. Logical single-qubit geometric $S^{(†)}$ and entangling two-qubit braiding operations are shown using two-physical-qubit joint measurements alone, while $T^{(†)}$ gates corresponding to a kind of partial-braiding operation require at least one three-qubit joint measurement. These relatively small-scale circuits demonstrate potential applications of both measurement-based geometric gates and a measurement-based demonstration of quantum Hamiltonian simulation.

We show that the average of the maximum teleportation fidelities between all pairs of nodes in a large quantum repeater network is a measure of the resourcefulness of the network as a whole. It can be used to rank networks of arbitrary topologies, with and without loops. For demonstration purposes, we use simple Werner state-based models to characterize some fundamental topologies (the star, the chain, some trees, and also the ring and the complete graph) with this measure in three (semi)realistic scenarios. Most of our results are analytic and apply to arbitrary network sizes. We identify the parameter ranges where these networks can achieve quantum advantages and show the large-$N$ behaviors.

Controlling both the magnitude and directionality of light scattering by subwavelength objects plays a crucial role in enhancing light-matter interactions and has great potential in antenna design, sensing, and optical displays. Superscattering, induced by degenerate resonances, allows the scattering cross section of subwavelength structures to surpass the fundamental single-channel limit. However, most existing superscattering techniques depend on complex multilayered structures and primarily aim to enhance scattering magnitudes. In this work, we propose a single-layer plasmonic core-shell nanoparticle that achieves superdirectional scattering without relying on high-permittivity materials and magnetic resonances. We demonstrate that for nanoparticles with a thin plasmonic nanoshell, both dielectric dipolar and quadrupolar resonances occur at nearly the same frequency, where the permittivity of the plasmonic shell approaches zero (degenerate epsilon-near-zero (ENZ) resonances), enabling superscattering in this simple nanoparticle. Furthermore, by tuning the amplitudes of these ENZ resonances, we show that both zero-backward and super-forward scattering can be realized. This approach, relying solely on pure electric ENZ modes in a simple core-shell nanoparticle, offers a new pathway for achieving superdirectional scattering and holds significant potential for applications in photovoltaic devices, biosensors, and nanoantennas.

We introduce a new mean-field equation for modeling Fabry-Perot resonators filled with a dispersive medium exhibiting both Brillouin and Kerr nonlinearities, e.g., an optical fiber. This model is derived from a unified framework that accounts for Brillouin scattering and four-wave mixing. It involves two coupled nonlinear Schrödinger equations for the forward and backward propagating fields, alongside a single equation governing the acoustic oscillation. Under the standard assumptions for the mean-field approach (high finesse, weak nonlinearity, and weak dispersion) we demonstrate that our model closely matches the original system. The simplified and elegant mathematical structure of our equation provides valuable physical insights. As a key example, we derive an expression for the growth rate of harmonic perturbations to the steady states. Additionally, our model facilitates fast and accurate numerical simulations using standard Fourier split-step methods. We highlight the effectiveness of this approach by simulating frequency comb generation in state-of-the-art high-Q fiber Fabry-Perot resonators.

Long-range optical pulling is highly desired for nanoscale manipulation, including biomolecules and functional particles. However, its realization in a homogeneous medium remains challenging due to the absence of strong scattering asymmetry. Here, we introduce an ingenious mechanism to obtain optical pulling and pushing forces using a metasurface-engineered optical field with a tailored longitudinal chirality gradient. This approach exploits parity-asymmetric interactions between chiral particles and the metasurface-engineered needle-like optical field, eliminating the need for complex background structures. Leveraging the field manipulation versatility of spin-decoupled metasurfaces, we demonstrate enantiomer separation across thousands of particle diameters—exceeding previous works by an order of magnitude in terms of particle-scale displacement. Furthermore, by tuning the chirality density of the field, directional control of particle motion can be achieved, underscoring its potential for large-scale chiral sorting and enantioselective drug purification.

Non-Hermitian photonics has attracted significant interest and influences several key areas such as optical metamaterials, laser physics, and nonlinear optics. While non-Hermitian effects have been widely addressed in two-dimensional (2D) systems, we focus on realistic three-dimensional devices. To this end we generalize established phase-space methods from mesoscopic optics and introduce Husimi functions for three-dimensional systems that deepen the insight and access to the mode morphology and their dynamics. We illustrate that four-dimensional Husimi functions can be represented using a specific projection on two dimensions and illustrate it for (conical) cylindrical cavities. The non-Hermitian character of the intrinsically open photonic systems is in particular revealed when examining the transverse electric and transverse magnetic polarization character of the resonance modes. Unlike the 2D case, polarization is not conserved in three-dimensional cavities, and we use generalized Husimi function to represent the interaction of polarization modes. We find their dynamics to be ruled by a network of exceptional points in the parameter space spanned by the refractive index and the cavity geometry tilt angle. This approach not only enhances our understanding of cavity modes but also aids in the design of more efficient photonic devices and systems.

Traditionally, observation of optical interference in intensity requires the balance of the paths of the two interfering fields within the coherence length of the optical fields. With intensity correlation fourth-order measurement between two detectors, such a requirement can be relaxed. Here, we report the observation of interference in a path-unbalanced Mach-Zehnder interferometer by mixing the output field with a weak coherence reference field before making a fourth-order intensity correlation measurement. Detailed theoretical analysis is made and is consistent with the experimental observation. As a side product of the study, when the coherent reference field is not present, the path-unbalanced interferometer realizes a Hong-Ou-Mandel interference effect that can be used to measure the coherence time of the input field with $g^{\left(2\right)}=1$. Such a technique of recovering interference, which is otherwise absent with the traditional observation method, should find wide applications in optical sensing by extending the applicable range.