Polarization-dependent dynamical properties of light such as the spin angular momentum (SAM), helicity, and chirality are conserved quantities in free space. Despite their similarities on account of their relationship with a circular state of polarization, SAM, helicity, and chirality emerge from distinct symmetries, which endows them with different physical meanings, properties, and practical applications. In this work we investigate the behavior of such quantities in time-varying media (TVM), i.e., how a temporal modulation impacts their symmetries and conservation laws. Our results demonstrate that the SAM is conserved for any time modulation, helicity is only preserved in impedance-matched time modulations, and chirality is not conserved. In addition, the continuity equations highlight the dependence of the chirality on the energy content of the fields. These results provide additional insights into the similarities and differences between SAM, helicity, and chirality, as well as their physical meaning. Furthermore, our theoretical framework provides an alternative perspective to analyze polarization-dependent light-matter interactions in TVM.

How to make a material antireflective without changing its high refraction index? Achieving antireflection in high-refractive-index materials poses challenges due to their high reflectivity (Fresnel equations). Based on theory with new boundary conditions, we propose modifying surface properties on a nanoscale to tackle this. Our study on weakly rough opaque surfaces reveals significant changes in specular and diffuse scattering, predicting antireflection where roughness matches light penetration depth. Experimental validation on nanoroughened Si films (at wavelengths 300 to 400 nm) supports our findings. We also analyze angular and polarization dependences of nanoroughness-induced haze, showing predominant $p$ polarization and minimal haze at nanoscale, yet impactful specular reflection reduction.

Hamiltonian simulation is one of the most promising applications of quantum computers, and the product formula is one of the most important methods for this purpose. Previous related work has mainly focused on the worst-case, average-case, or actual-case scenarios. In this work we consider the simulation error under a fixed observable. Specifically, errors that commute with this observable become less significant. To illustrate this point, we define the observation error as the expectation under the observable and provide a commutativity-based upper bound using the Baker-Campbell-Hausdorff formula. Furthermore, we observe that the evolution order plays a critical role in determining the observation error. By leveraging a simulated annealing algorithm, we design an evolution order optimization algorithm, to identify an order that enhances commutativity with the observable, where the observation error indicated by this upper bound can be significantly compressed. In the experiment with the Heisenberg model, the observation bound compresses the Trotter number by nearly half compared to recent commutator bounds. The experiment on the hydrogen molecule Hamiltonian demonstrates that optimizing the order can lead to nearly half the reduction in the Trotter number.

We construct a sequence of multisite gates which transform an easily constructed product state into an approximation to the superfluid ground state of the Bose-Hubbard model. The mapping is exact in the one-dimensional hard-core limit and for noninteracting particles in both one and two dimensions. The gate sequence has other applications, such as being used as part of a many-body interferometer which probes the existence of doublons.

The interaction of twisted photons with atoms and molecules has garnered significant interest in recent decades. It has been established that, in the case of randomly distributed targets, the cross sections do not depend on the orbital angular momentum of the twisted projectile, thus ruling out helical dichroism. However, examining the impact-parameter-independent and -dependent cross sections, as demonstrated in the twisted-photon-induced single ionization of the ${\mathrm{N}}_{2}1{\sigma }_g$ orbital, the findings suggest that helical dichroism can be primarily observed in the impact-parameter-dependent cross sections for the photoelectron emitted in twisted light propagation direction, for both the radial and angular components. This comprehensive study not only clarifies the mechanisms underlying helical dichroism but also enhances our understanding of the complexities of twisted-photon scatterings.

Recently, we have visually elucidated the dynamics of the high-order harmonic process of an asymmetric CO molecule with a few-cycle laser pulse using the Bohmian perspective and found that only one central trajectory, BT(P), whose initial start is near the C atom, principally contributes to the high-energy part of the harmonic spectrum. The role of the other central trajectory originating near the O atom, BT(N), remains a question of interest. The present study shows the non-negligible contribution of the BT(N) to cause a frequency shift in the high harmonic spectrum when using a laser pulse with more optical cycles. Indeed, when the molecule is oriented antiparallel to the laser's electric polarization, analyzing the acceleration profiles and harmonic spectra reveals that despite smaller weight contributing to the harmonic intensity, BT(N) is significant in reproducing the harmonic spectrum structure, especially in the cutoff-energy region. The BT(N) contribution modulates the dynamical phase at the emission time, altering the dynamical phase difference between two consecutive emission bursts. This modification leads to a blueshift of harmonic orders in the cutoff region compared to the scenarios without BT(N) contribution, bringing the harmonic spectrum from the combination BTs($\mathrm{P}+\mathrm{N}$) closer to the result of directly solving the time-dependent Schrödinger equation. This finding confirms the nonlocality of the quantum process via the Bohmian perspective that central trajectories contain all the essential dynamic information of high-order harmonic generation.

We propose an alternative experimentally feasible approach to achieve high-efficiency ground-state cooling of a mechanical oscillator in an optomechanical system under the deeply unresolved sideband condition with the assistance of both intracavity and extracavity squeezing. In the scheme, a degenerate optical parametric amplifier is placed inside the optical cavity, generating the intracavity squeezing; in addition, the optical cavity is driven by the extracavity squeezed light, namely the extracavity squeezing. The quantum interference effect generated by intracavity squeezing and extracavity squeezing can completely suppress the nonresonant Stokes heating process while greatly enhancing the anti-Stokes cooling process. Therefore, the joint-squeezing scheme is capable of cooling the mechanical oscillators to their quantum ground state in a regime far away from the resolved sideband condition. Compared with other traditional optomechanical cooling schemes, the single-photon cooling rate in this joint-squeezing scheme can be tremendously enlarged by nearly three orders of magnitude. At the same time, the coupling strength required to achieve ground-state cooling can be significantly reduced. This scheme is promising for cooling large-mass and low-frequency mechanical oscillators, which provides a prerequisite for preparing and manipulating nonclassical states in macroscopic quantum systems and lays a significant foundation for quantum manipulation.

This paper explores the possibility of designing nanoantennas that operate effectively in a wide range of infrared frequencies. To achieve a constant input impedance, we propose self-complementary nanoantennas composed of a high-permittivity dielectric and plasmonic metal. First, we present an approach to extend the applicability of Babinet's principle to the considered materials. We design several self-complementary nanoantennas made of silicon and silver with an optimal thickness of 12.7 nm whose input impedance is close to half the vacuum impedance, at least for frequencies from 50 THz to 300 THz. This approach facilitates the design of broadband nanoantennas operating in infrared.

Variational quantum algorithms show potential in effectively operating on noisy intermediate-scale quantum devices. A variational approach to reinforcement learning has been recently proposed, incorporating linear-optical interferometers and a classical learning model known as projective simulation (PS). PS is a decision-making tool for reinforcement learning and can be classically represented as a random walk on a graph that describes the agent's memory. In its optical quantum version, this approach utilizes quantum walks of single photons on a mesh of tunable beamsplitters and phase shifters to select actions. In this work, we present the implementation of this algorithm on Ascella, a single-photon-based quantum computer from Quandela. The focus is drawn on solving a test bed task to showcase the potential of the quantum agent with respect to the classical agent.

This paper discusses the formation of ultracold YbAg molecules via photoassociation, following the proposal of using YbAg as a promising molecular candidate for electron electric dipole moment experiments [M. Verma et al. Phys. Rev. Lett. 125, 153201 (2020)]. Our study utilizes high-level ab initio calculations, encompassing both multireference configuration interaction, relativistic Fock-space coupled cluster, and Kramers-restricted configuration interaction methods, to investigate the electronic structures including potential energy curves, spectroscopic constant, vibrational energy levels, and associated transition dipole moment and Franck-Condon factors for 28 electronic states. By choosing (5)($\mathrm{\Omega }=3/2$) as the intermediate state, we discuss the feasibility of forming ultracold YbAg molecules through stimulated Raman adiabatic passage method.

In this study, we integrate experimental observations and theoretical models to elucidate the complex phenomena observed in the resonant S $K$-edge KLL Auger scattering spectra of the ${\mathrm{SF}}_6$ molecule. A two-dimensional spectral map, constructed of incident photon energy and kinetic energy of the emitted Auger electron, is shown to be a versatile tool for understanding a character of the core-excited potential energy surface and change of the molecular geometry. Our findings reveal how the distinct dispersion behavior of multiple spectral lines enables mapping of ultrafast dynamics within the short-lived core-excited states. Our results confirm the presence of nuclear dynamics in the $\mathrm{S}1s^{-1}6a_{1g}^1$ and $\mathrm{S}1s^{-1}6t_{1u}^1$ core-excited states, while dynamics is absent in the $\mathrm{S}1s^{-1}7t_{1u}^1$ state. Using a combination of ab initio analysis, simulations with Coulomb model potentials, and a simple analytical approximation, we qualitatively demonstrate how the varying characteristics of spectral dispersion—classified as Raman, non-Raman, and anti-Raman—mirror the relative gradients of the intermediate and final states in the resonant x-ray scattering process. This insight allows for the effective mapping of molecular potential energy curves, offering a prospective tool on the underlying mechanisms of resonant Auger scattering and its potential for probing molecular dynamics.

The method of effective modes is used for quantifying the dynamics of energy redistribution between different kinds of motions in water clusters upon their excitation within the long-wavelength infrared range $<2000 \mathrm{c}{\mathrm{m}}^{-1}$. Three kinds of vibrations were considered, namely, radial and angular distortions of H bonds and bending vibrations of the molecules. Dynamics of the clusters (described in the Born-Oppenheimer approximation with the electronic problem solved at the MP2 level) was promoted by the initial excitation of particular kinds of motions or their combinations with the total activation energy per molecule in a range of 1.2–4.6 kcal/mol. Gross contributions of the different kinds of motion to the leading effective modes of clusters were determined as functions of time, which made it possible to estimate the dynamic coupling. The coupling of motions depends on the number of water molecules as well as on the activation energy and its initial distribution over particular degrees of freedom. The energy initially concentrated on radial distortions can be transferred directly to the angular distortions, and the corresponding mean dynamic coupling parameter reaches a maximum of $5.0\times {10}^{11}$ to $6.0\times {10}^{11}{\mathrm{s}}^{-1}$ at the initial kinetic energy per molecule ∼3.2–3.5 kcal/mol. It decreases with an increase in the flexibility of the cluster. When the energy is initially concentrated on the angular distortion modes, its relaxation toward the lower-frequency radial modes is usually indirect and requires the mediating role of bending vibrations whose temporary contribution to the dynamics can be as high as 25–30%. The angular-to-radial distortion coupling parameter is lower by nearly half than the radial-to-angular one. When angular distortions are initially activated concurrently with the bending vibrations, the prevailing energy relaxation channel is the activation of radial distortions. Upon the initial excitation of bending vibrations, the energy can be kept by the modes with no noticeable redistribution for up to 2 or 3 ps, being later redistributed in a cascade process at first to angular and then to radial distortions.

A rigorous treatment of light-matter interactions typically requires an interacting quantum field theory. However, most applications of interest are handled using classical or semiclassical models, which are valid only when quantum-field fluctuations can be neglected. This approximation breaks down in scenarios involving large light intensities or degenerate matter, where additional quantum effects become significant. In this work, we address these limitations by developing a quantum kinetic framework that treats both light and matter fields on equal footing, naturally incorporating both linear and nonlinear interactions. To accurately account for light fluctuations, we introduce a photon distribution function that, together with the classical electromagnetic fields, provides a better description of the photon fluid. From this formalism, we derive kinetic equations from first principles that recover classical electrodynamical results while revealing couplings that are absent in the corresponding classical theory. Furthermore, by addressing the Coulomb interaction in the Hartree-Fock approximation, we include the role of fermionic exchange exactly in both kinetic and fluid regimes through a generalized Fock potential. The latter provides corrections not only to the electrostatic forces but also to the plasma velocity fields, which become significant in degenerate conditions.

We study the thermal effects of the multiphoton Jaynes-Cummings model (JCM) using a thermofield dynamics (TFD) method. Letting the initial state of the whole system for the multiphoton JCM be a product of the ground state of an atom and a coherent state of a cavity field at finite temperature, we compute its time evolution. We evaluate a period of the collapse and revival of the Rabi oscillations and the relative entropy of coherence of the atom up to the second-order perturbation of the low-temperature expansion. We show that an intuitive estimation of the period matches the result of the perturbation theory of TFD well. In particular, we see that the period of the two-photon JCM hardly depends on the amplitude of the coherent state of the cavity field or the temperature. Numerical calculations suggest that the relative entropy of coherence of the two-photon JCM does not decay even for nonzero-temperature cases as time proceeds. By contrast, the relative entropies of coherence for single-, three-, and four-photon JCMs decay as time proceeds for zero- and finite-temperature cases.

Coupled angular-momentum eigenstates are widely used in atomic and nuclear physics calculations and are building blocks for spin networks and the Schur transform. To combine two angular momenta ${\mathbf{J}}_1$ and ${\mathbf{J}}_2$, forming eigenstates of their total angular momentum $\mathbf{J}={\mathbf{J}}_1+{\mathbf{J}}_2$, we develop a quantum-walk scheme that does not require inputting $O\left(j^3\right)$ nonzero Clebsch–Gordan (CG) coefficients classically. In fact, our scheme may be regarded as a unitary method for computing CG coefficients on quantum computers with a typical complexity of $O\left(j\right)$ and a worst-case complexity of $O\left(j^3\right)$. Equivalently, our scheme provides decompositions of the dense CG unitary into sparser unitary operations. Our scheme prepares angular-momentum eigenstates using a sequence of Hamiltonians to move an initial state deterministically to desired final states, which are usually highly entangled states in the computational basis. In contrast with usual quantum walks, whose Hamiltonians are prescribed, we engineer the Hamiltonians in $\text{su}\left(2\right)\times \text{su}\left(2\right)$, which are inspired by, but different from, Hamiltonians that govern magnetic resonances and dipole interactions. To achieve a deterministic preparation of both ket and bra states, we use projection and destructive interference to double pinch the quantum walks, such that each step is a unit-probability population transfer within a two-level system. We test our state preparation scheme on classical computers, reproducing tables of CG coefficients. We also implement small test problems on current quantum hardware.

In this paper, we propose two uncertainty relations that reveal a previously unnoticed complementarity in quantum uncertainty not captured by the conventional Robertson and Schrödinger relations, particularly in the case of mixed quantum states. These relations are formulated based on the state-dependent norm of the commutator, generalizing the Böttcher-Wenzel inequality. Furthermore, we compare our results with the Luo-Park uncertainty relation and demonstrate that our bound outperforms their bound for mutually unbiased observables.

We study restrictions of two-body correlations in three-qubit states, using three local-unitarily invariant coordinates based on the Bloch vector lengths of the marginal states. First, we find tight nonlinear bounds satisfied by all pure states and extend this result by including the three-body correlations. Second, we consider mixed states and conjecture a tight nonlinear bound for all three-qubit states. Finally, within the created framework, we give criteria to detect different types of multipartite entanglement as well as characterize the rank of the quantum state.

As the demand for quantum networks and communication grows, identifying quantum nonlocality in these networks has become a crucial and challenging task. The nonconvex nature of the network local set makes traditional Bell-type inequalities inadequate for detection. Machine learning algorithms have emerged as a promising approach to address this issue. In this study we introduce a quantifier for nonlocality in chain-shaped quantum networks and employ deep-learning algorithms for its detection. We validate this method using the trilocal network, adopting an ensemble learning strategy called the stacking method, which combines four distinct deep neural networks to train a linear regression model. Our results show that machine learning effectively quantifies nonlocality in chain networks and exhibits strong generalization capabilities for Werner states.

We present two protocols for realizing deterministic nonlocal multiqubit quantum gates on qubits coupled to a common cavity mode. The protocols rely only on a classical drive of the cavity mode, while no external drive of the qubits is required. Applied to just two qubits, both protocols provide a universal gate set for quantum computing, together with single-qubit gates. In the first protocol, the state of the cavity follows a closed trajectory in phase space and accumulates a geometric phase depending on the state of the qubits. This geometric phase gate can be used together with global single-qubit gates to generate high-fidelity Greenberger–Horne–Zeilinger (GHZ) states. The second protocol uses an adiabatic evolution of the combined qubit-cavity system to accumulate a dynamical phase. Repeated applications of this protocol allow for the realization of a family of phase gates with arbitrary phases, e.g., phase-rotation gates and multi-controlled-Z gates. For both protocols, we provide analytic solutions for the error rates, which scale as $\sim N/\sqrt{C}$ in the presence of relevant losses, with $C$ the cooperativity and $N$ the qubit number. Our protocols are applicable to a variety of systems and can be generalized by replacing the cavity by a different bosonic mode, such as a phononic mode. We provide estimates of gate fidelities and durations for atomic and molecular qubits as well as superconducting fluxonium qubits coupled to optical or microwave cavities, and we outline implications for quantum error correction.