Optical systems breaking Lorentz reciprocity have attracted broad attention due to their intriguing physics and applications. Nonreciprocal metasurfaces can enable one-way light transmission and reflection with essential applications in optical communication. Conventional nonreciprocal metasurfaces rely on using magneto-optic or nonlinear materials to induce nonreciprocal optical properties. Here we propose and demonstrate an alternative mechanism for realizing nonreciprocal metasurfaces based on the relativistic effect of a moving medium. The metasurface is composed of periodic spinning dielectric cylinders located above a dielectric substrate. The spinning motion breaks the time-reversal symmetry and induces bi-anisotropic Tellegen-type response of the meta-atoms. We show that the metasurface can realize both asymmetric and nonreciprocal manipulations of the incident plane wave. The underlying mechanism is attributed to the Sagnac effect associated with the chiral multipole modes of the coupled spinning cylinders. By introducing dielectric pillars to modulate the phase profile, the metasurface can enable nonreciprocal wavefront manipulations. Our work offers a mechanism for realizing nonreciprocal light manipulation in free space. The proposed metasurface can serve as a platform to explore the interesting physics of nonreciprocal optics, non-Hermitian optics, and topological photonics.

Generalized eigenvalue equations describe the band structures of various metamaterials, where complex bands can emerge even if the involved matrices are Hermitian. In this paper, we provide a geometrical understanding of the real-complex transition of the band structures. Specifically, our analysis, based on auxiliary eigenvalues, clarifies the correspondence between the real-complex transition of the generalized eigenvalue equations and the Lifshitz transition in electron systems. Furthermore, we demonstrate that real (complex) bands of a photonic system correspond to the Fermi surfaces of type-II (type-I) Dirac cones in electron systems when the permittivity $\varepsilon$ and the permeability $\mu$ are independent of frequency. In addition, our analysis reveals that exceptional points are induced by the frequency dependence of permittivity $\varepsilon$ and permeability $\mu$ in our photonic system.

The coupling among plasmonic excitations of the nanoparticle complex plays an important role in the responses of optical nanocircuits with multifunction in signal processing. We develop an equivalent circuit model based on the loop matrix method to explore the coupling effects in the complex of nanorods. Our analytical results supported by finite-difference time-domain simulations not only give the resonance characters of (screening) bonding mode, antibonding mode, and charge-transfer plasmon (CTP) mode simultaneously, but also reveal the physics picture of the screening bonding dipole plasmon (BDP) and CTP with common origin (the remnants of multipole plasmonic modes). It is found that the resonance wavelength of the CTP depends sensitively on the length of the conductive bridge connecting the nanorods, showing factor 10 enhancement of measurement (of the interparticle gap size) sensitivity as a nanoruler compared with that based on the BDP, while with changing the bridge width there is a switch of the mode nature with associated change of far-field scattering patterns. In addition, interparticle coupling induced Rabi splitting, Fano effect, and dual CTPs have been found. Our studies provide a new analytical perspective on the electromagnetic coupling mechanism of nanocomposites and establish a foundation for the design of nanocircuits and micro-nano-optical devices.

In this work, we experimentally demonstrate the quantum interference of force effect using pairs of entangled photons. Although photons are massless particles, they have linear momentum, and our experiments show that the quantum superposition of a positive momentum transfer with a null momentum transfer may result in a negative momentum transfer to an ensemble of quantum particles (photons), a behavior with no classical analog. The momentum transfer to each photon is defined by the result of a polarization measurement performed in a second photon, initially entangled with it.

We propose a framework for simulating the real-time dynamics of quantum field theories using continuous-variable quantum computing (CVQC). Focusing on ($1+1$)-dimensional ${\phi }^4$ scalar field theory, the approach employs the Hamiltonian formalism to map the theory onto a spatial lattice, with fields represented as quantum harmonic oscillators. Using measurement-based quantum computing, we implement non-Gaussian operations for CQVC platforms. The study introduces methods for preparing initial states with specific momenta and simulating their evolution under the ${\phi }^4$ Hamiltonian. Key quantum objects, such as two-point correlation functions, validate the framework against analytical solutions. Scattering simulations further illustrate how mass and coupling strength influence field dynamics and energy redistribution. Thus, we demonstrate CVQC's scalability for larger lattice systems and its potential for simulating more complex field theories.

State-selective single- and double-electron capture in collisions of ${\mathrm{N}}^{4+}$ ions with He atoms have been studied at projectile energies in the range of 20–80 keV. The state-selective single- and double-electron capture cross sections and projectile scattering angle distributions were obtained using cold-target recoil-ion momentum spectroscopy. For single-electron capture, the experimentally obtained state-selective cross sections show an obvious discrepancy with the calculated results by molecular orbital close-coupling methods and are in good agreement at a projectile energy of 20 keV with other experiments. The angular distributions are compared with calculations from the multichannel Landau-Zener model. For double-electron capture, electrons captured into $2l2l^{\prime }$ states of the ${\mathrm{N}}^{4+}$ projectile are dominant. The angular distributions are explained by a two-step model combining the classical deflection function.

We investigate the transfer of longitudinal orbital angular momentum (OAM) from a twisted light beam to an electron through the photoionization of a hydrogen atom. Our theoretical analysis employs an asymptotic Laguerre-Gaussian (LG) beam, a form of LG beam with a higher radial index, whose spatial complex field amplitude closely resembles that of an ideal Bessel beam. We show that the outgoing electron acquires a well-defined OAM projection when the hydrogen atom is located along the propagation axis of the twisted photon. Additionally, we find that the transverse spatial structure of the outgoing electron mirrors the higher-order Bessel profile, characterized by an intensity null at the center and multiple off-axis rings. Our findings offer a practical and experimentally feasible approach for generating Bessel electron vortex beams, providing a significant advancement in this area of research.

In this work we present a model for the paraxial propagation of linearly polarized vector beams. Of particular importance is the appearance of a transverse momentum term proportional to the linear polarization angle gradient imparted to the beam during the beam preparation process. The model predicts that during propagation, this momentum will be exchanged for classical transverse momentum, thereby causing the beam to accelerate. We observe the momentum exchange in experiment by designing the polarization profile in such a way to cause the beam centroid to follow a parabolic path through free space.

We introduce the conformally invariant scalar product, originally devised for radiation fields, to the study of the modes of optical resonators. This scalar product allows one to normalize and compare resonant modes using their corresponding radiation fields. Such fields are polychromatic fields free of divergences, which are determined from the complex frequencies and the modal fields on the surface of the resonator. The scalar product is expressed as surface integrals involving the modal fields, multiplied by closed-form factors incorporating the complex frequencies. In a practical application, we study the modes of disk-shaped whispering gallery resonators and show that the proposed scalar product accurately predicts the geometry-dependent anticrossings between modes.

Spontaneous collapse models aim to solve the long-standing measurement problem in quantum mechanics by modifying the theory's dynamics to include objective wave-function collapses. These collapses occur randomly in space, bridging the gap between quantum and classical behavior. A central feature of these models is their dependence on mass density, which directly influences how and when collapse events occur. In this work, we explore a generalized framework in which the collapse dynamics depend on arbitrary functions of the mass density, extending previous models. We analyze the theoretical consistency of these generalizations, investigate their predictions, and compare them with experimental data. Our findings show that only a limited range of mass-dependence functions are viable, with significant implications for the future development and empirical testability of collapse-based models. Importantly, they also indicate that a well-justified model denoted here as PSL shows much more resilience to experimental falsification than standard collapse models.

Embezzlement of entanglement is the counterintuitive process in which entanglement is extracted from a resource system using local unitary operations, with almost no detectable change in the resource's state. It was recently argued that any state of a relativistic quantum field theory can serve as a resource for perfect embezzlement. We study the circuit complexity of embezzlement using sequences of states that enable arbitrary precision for the process, commonly called universal embezzling families. In addition, we argue that this approach provides a well-defined model for the complexity of embezzlement from quantum field theories. Under fairly general assumptions, we establish a generic lower bound on the complexity, which increases with the precision of the process or the amount of embezzled entanglement, and diverges as either becomes infinite. As an example, we consider a one-dimensional critical system as the resource and derive an exponentially growing lower bound on the complexity. Consequently, the findings imply that circuit complexity acts as a physical obstruction to perfect embezzlement. Supplementary to the main results, we derive lower bounds for common models of circuit complexity for state preparation based on the difference between the Schatten norms of the initial and final states.

In this paper, we will show how finite-temperature corrections and spin-dependent/independent noise will affect the contrast in a matter-wave interferometer, especially with massive objects and large spatial superposition sizes. Typically, spin is embedded in a nanoparticle as a defect, which can be manipulated by the external magnetic field to create a macroscopic quantum superposition. These massive matter-wave interferometers are the cornerstone for many new fundamental advancements in physics; particularly, macroscopic quantum superposition can use entanglement features to, e.g., test physics beyond the Standard Model, test the equivalence principle, improve quantum sensors, and test the quantum nature of spacetime in a laboratory. We will consider a Stern-Gerlach-type apparatus to create macroscopic quantum superposition in a harmonic oscillator trap, and figure out the spin contrast loss due to linear spin-independent and spin-dependent noise in a single interferometer. We will show that spin contrast loss due to spin-independent noise does not depend on the initial thermal state of the matter wave function. However, spin contrast loss due to spin-dependent fluctuations is dependent on the initial thermal occupation of the quantum state. We will keep our discussion general as far as the noise parameters are concerned.

The nonlinear dynamics of quantum droplets in a quasi-one-dimensional BEC loaded in a two-core trap potential are investigated. The cases of standing and moving quantum droplets are considered. The frequencies of the Josephson oscillations and the condition for self-trapping are found. An analytical description is based on the variational approach to a system of coupled extended Gross-Pitaevskii (EGP) equations, including Lee-Huang-Yang correction terms. In the case of moving droplets, the system of equations describing the coupling of the relative motion of droplets in two cores with the dynamics of the relative phase and population imbalance (Josephson currents) is derived. Different regimes of droplet dynamics are found, including attraction and repulsion in dependence on the relative phase evolution. These phenomena are the realization of the Andreev-Bashkin effect for superfluids in a two-core trap potential. Analytical predictions of the model are confirmed by full numerical simulations of the coupled extended Gross-Pitaevskii equations.

We discuss the progress on exactly solvable multistate Landau-Zener models from a perspective of their application to competing reactions of particle creation from a false vacuum. Such models generally predict that, even with identical initial conditions, and for nearly the same other particle parameters, a quantum coherent evolution results in a final particle distribution with significant asymmetry. We use an exact solution of the driven bosonic Tavis-Cummings model for two reaction pathways in order to quantify this effect, reveal a corresponding phase transition, and identify its universality class.

Within the framework of optical Dirac theory, we present a field-theoretical model of spin-orbit interaction and photonic spin and orbital Hall effects. Our approach reformulates light propagation along helical paths as solving the Maxwell equations in a ray-based curvilinear coordinate system. This system can alternatively be interpreted as a spin-degenerate medium with antisymmetric elements in the dielectric tensor, corresponding to the spin-1 excitation mode characterized by a rotational dipole vector. We show that, at leading order, the resulting effective Hamiltonian is equivalent to the Maxwell theory in a uniformly rotating frame, incorporating both spin-rotation and orbit-rotation coupling. This rotation arises from the torsion of helical paths, manifesting as extrinsic orbital angular momentum (EOAM) of photons. Notably, the spin angular momentum of the photon and its intrinsic orbital angular momentum contribute jointly to the geometric phase. In the Heisenberg picture, the spin and orbital Hall effects naturally emerge from interaction terms in the ray equations. Furthermore, we find that the transverse spin of evanescent waves couples with EOAM, revealing that the geometric phase of elliptically polarized light differs from that of circularly polarized light. This distinction underscores the role of spin-orbit coupling in modifying phase accumulation.

Quantum optics plays a crucial role in developing quantum computers on different platforms. In photonics, precise control over light's degrees of freedom—including discrete variables (polarization, photon number, orbital angular momentum) and continuous variables (phase, amplitude quadratures, frequency)—is fundamental. Our model manipulates photonic systems to encode and process quantum information via the photon's spatial degree of freedom, employing polarization as an auxiliary qubit. We propose a programmable photonic circuit that simulates quantum channels, including phase-damping, amplitude-damping, and bit-flip channels, through adjustable interferometric parameters. Furthermore, the interferometer extends to more complex channels, such as the squeezed generalized amplitude damping. This work contributes to advancing quantum simulation techniques and serves as a foundation for exploring quantum computing applications, while highlighting pathways for their practical implementation.

Molecular polaritons are becoming one of the leading directions to control a multitude of chemical and physical processes, such as charge transfer, selective bond breaking, and excited-state dynamics. Accurately and efficiently simulating polariton properties under the collective-coupling regimes (between $N$ molecules and the cavity mode) remains a central theoretical challenge. In this work, we use a stochastic resolution of the identity approach coupled with a Chebyshev expansion to compute various polariton photophysical properties, with a substantially reduced computational effort than would be needed for a direct diagonalization of the same Hamiltonian, which is often the bottleneck for such large dimensionality. Such quantities of interest are the total density of states (the eigenspectrum of the Hamiltonian) and the transmission spectrum (a probe of the photonic degrees of freedom), the latter of which is a direct observable in the experiment. We simulate the linear spectroscopy of molecule-cavity hybrid systems, specifically exploring the effects of the distribution and magnitude of molecular disorder for one, few, and many coupled molecules. We compare our numerical results to recent work, which formulated analytic expressions in the large-$N$ limit for the spectroscopic signals. We find that our results match those of the analytic results when $N=100$, at which point we find that the collective effects for linear spectroscopy are converged.