We theoretically propose the realization of a three-dimensional (3D) spin Hall effect (SHE) of light by tightly focusing a linearly polarized light. Owing to the spin-orbital interaction in focusing, the left and right circularly polarized components of light are partly converted into each other, acquiring opposite vortex phases. As the superposition of the vortex and the initial vortex-free light, the two polarized components exhibit spiral intensity patterns which rotate oppositely around the propagation axis. Consequently, the two spin components are distributed alternatively in both the azimuthal and the longitudinal directions, leading to a 3D array of split spin components, and the transverse intensity is also spit asynchronously. Moreover, that array is rotatable by the incident polarization, and the longitudinal spacing in the array can be controlled by the numerical aperture of the lens. The 3D SHE of light finds an additional degree of freedom available to control the spin state of the photon, which may be valuable in optical manipulation and quantum information.

An approach to quantization of the damped harmonic oscillator (DHO) is developed on the basis of a modified Bateman Lagrangian (MBL); thereby some quantum mechanical aspects of the DHO are clarified. We treat the energy operator for the DHO, in addition to the Hamiltonian operator that is determined from the MBL and corresponds to the total energy of the system. It is demonstrated that the energy eigenvalues of the DHO exponentially decrease with time and that transitions between the energy eigenstates occur in accordance with the Schrödinger equation. Also, it is pointed out that a new critical parameter discriminates different behaviors of transition probabilities.

We derive a trade-off relation between accuracy of implementing a desired unitary evolution using a restricted set of free unitaries and the size of the assisting system, in terms of the resource generating and losing capacity of the target unitary. In particular, this relation implies that, for any theory equipped with a resource measure satisfying lenient conditions, any resource changing unitary cannot be perfectly implemented by a free unitary applied to a system and an environment if the environment has finite dimensions. Our results are applicable to a wide class of resources including energy, asymmetry, coherence, entanglement, and magic, imposing ultimate limitations inherent in such important physical settings, as well as providing insights into operational restrictions in general resource theories.

We study the creation process of an electron-positron pair as a result of the collision between two incoming photons with full spatial and temporal resolution. The dynamics of the four involved particles is described by a simplified model based on a Yukawa Hamiltonian in one spatial dimension. This quantum field theoretical approach permits us to go beyond the usual external field approximation and to study the depletion of the two colliding photon wave packets due to the back reaction of the created electron-positron pair. If the spatial extension of the incoming photons is sufficiently narrow, we predict an interesting blueshift with regard to the optimum incoming photon momentum that can maximize the pair-creation yield close to the threshold momentum.

We present results on the accurate one-dimensional (1D) modeling of simple atomic and molecular systems excited by strong laser fields. We use atomic model potentials that we derive from the corrections proposed earlier using the reduced ground-state density of a three-dimensional (3D) single-active electron atom. The correction involves a change of the asymptotics of the 1D Coulomb model potentials while maintaining the correct ground-state energy. We present three different applications of this method: we construct correct 1D models of the hydrogen molecular ion, the helium atom, and the hydrogen molecule using improved parameters of existing soft-core Coulomb potential forms. We test these 1D models by comparing the corresponding numerical simulation results with their 3D counterparts in typical strong-field physics scenarios with near- and mid-infrared laser pulses, having peak intensities in the ${10}^{14}-{10}^{15}\mathrm{W}/{\mathrm{cm}}^2$ range, and we find an impressively increased accuracy in the dynamics of the most important atomic quantities on the time scale of the excitation. We also present the high-order harmonic spectra of the He atom, computed using our 1D atomic model potentials. They show a very good match with the structure and phase obtained from the 3D simulations in an experimentally important range of excitation amplitudes.

When the molecules with degenerate current-carrying orbitals are exposed to the bichromatic counterrotating circularly polarized (BCCP) laser fields, the destructive interference between high harmonics from these orbitals results in a strong suppression of harmonic emission with the selected helicity. As a result, there are large intensity differences between the high harmonics with opposite helicities in a wide spectral range. This interference effect is related to the noncylindrical symmetry of the molecular current-carrying orbitals and therefore depends on the relative orientation between the molecule and the driving laser fields. Furthermore, our results show that this interference can be controlled by adjusting the relative intensity ratio of the BCCP field. Finally, we show that highly elliptically polarized attosecond pulses can be generated by using this interference and their ellipticities can be tuned by controlling the molecular orientation.

We study the nonlinearities due to direct perturbation to the dark state in coherent population trapping (CPT). To extract the susceptibilities of the CPT atoms with respect to probe fields, we treat the CPT dressing fields as control parameters and redefine susceptibilities with respect to the probe fields alone. With such a redefinition, we reveal that a CPT-based system displays an ultralarge, resonantly enhanced second-order cross susceptibility ${\chi }^{\left(2\right)}$ together with vanishing linear absorption. Physically, this effect is based on the CPT dark-state shift, which is traced to the six-photon parametric processes for all involved fields (including the dressing and probe fields). Because of the lack of the direct perturbation, this effect is absent in the electromagnetically induced transparency (EIT)-based system, in which only resonantly enhanced third-order (Kerr) susceptibility ${\chi }^{\left(3\right)}$ is obtainable but much weaker than the second-order one. The second-order nonlinearity, because of its stronger effect, can be more sensitive for quantum nonlinear optics at low light levels than the third-order nonlinearity.

We theoretically study the magneto-optical manipulation of surface polaritons (SPs) in the negative index metamaterial–dielectric interface waveguide system. We analyze the linear and nonlinear propagation properties of the system when a weak gradient magnetic field is applied. A lossless superluminal SPs soliton is obtained via active Raman gain. We show that the SPs soliton will deflect in the weak gradient magnetic field (Stern-Gerlach-like effect); thus, the trajectory of SPs can be controlled by the gradient magnetic field, and dynamic control of SPs can also be realized by using a time-dependent gradient magnetic field. In addition, a “XNOR”-like logic gate is realized based on the trajectory control of SPs with external magnetic field and the interaction of the SPs soliton. This paper has certain theoretical significance for nanoscale optical information processing.

Gate-based quantum computers can in principle simulate the adiabatic dynamics of a large class of Hamiltonians. Here, we consider the cyclic adiabatic evolution of a parameter in the Hamiltonian. We propose a quantum algorithm to estimate the Berry phase and use it to classify the topological order of both single-particle and interacting models, highlighting the differences between the two. This algorithm is extensible to an interacting topological system. Our results evidence the potential of near-term quantum hardware for the topological classification of quantum matter.

In view of the fundamental importance and many promising potential applications, non-Abelian statistics of topologically protected states have attracted much attention recently. However, due to the operational difficulties in solid-state materials, experimental realization of non-Abelian statistics is lacking. The superconducting quantum circuit system is scalable and controllable, and thus is a promising platform for quantum simulation. Here we propose a scheme to demonstrate non-Abelian statistics of topologically protected zero-energy edge modes on a chain of superconducting circuits. Specifically, we can realize topological phase transition by varying the hopping strength and magnetic field in the chain, and the realized non-Abelian operation can be used in topological quantum computation. Considering the advantages of the superconducting quantum circuits, our protocol may shed light on quantum computation via topologically protected states.

Anyons in one spatial dimension can be defined by correctly identifying the configuration space of indistinguishable particles and imposing Robin boundary conditions. This allows an interpolation between the bosonic and fermionic limits. In this paper, we study the quantum entanglement between two one-dimensional anyons on a real line as a function of their statistics.

Electron affinities (EAs) of many lanthanide elements still remain unknown due to their complicated electronic structures and relatively low EA values. In the present work, we utilized the slow-velocity map-imaging method combined with an ion trap to resolve conundrums. The EA values of praseodymium, neodymium, and terbium are determined to be $881.0\left(37\right)\mathrm{c}{\mathrm{m}}^{-1}$ or 0.109 23(46) eV, $786.3\left(26\right)\mathrm{c}{\mathrm{m}}^{-1}$ or 0.097 48(31) eV, and $1059.1\left(64\right)\mathrm{c}{\mathrm{m}}^{-1}$ or 0.131 31(79) eV, respectively. We also observed several excited states of Pr, Nd, and Tb anions.

Nonequilibrium dynamics induced by rapid changes of external parameters is relevant for a wide range of scenarios across many domains of physics. For waves in spatially periodic systems, quenches will alter the band structure and generate new excitations. In the case of topological band structures, defect modes at boundaries can be generated or destroyed when quenching through a topological phase transition. Here, we show that optomechanical arrays are a promising platform for studying such dynamics, as their band structure can be tuned temporally by a control laser. We study the creation of nonequilibrium optical and mechanical excitations in one-dimensional arrays, including a bosonic version of the Su-Schrieffer-Heeger model. These ideas can be transferred to other systems such as driven nonlinear cavity arrays.

Experimental and theoretical studies of nonlinear frequency combs in ${\chi }^{\left(3\right)}$ optical microresonators attracted tremendous research interest during the last decade and resulted in prototypes of soliton-based steadily working devices. Realization of similar combs owing to ${\chi }^{\left(2\right)}$ optical nonlinearity promises new breakthroughs and is a big scientific challenge. We analyze the main obstacles for realization of the ${\chi }^{\left(2\right)}$ frequency combs in high-$Q$ microresonators and propose two families of steady-state nonlinear solutions, including soliton and periodic solutions, for such combs. Despite periodicity of light fields inside microresonators, the nonlinear solutions can be topologically different and relevant to periodic and antiperiodic boundary conditions. The antiperiodic states are expected to be the most favorable for the comb generation. The found particular solutions exist owing to a large difference in the group velocities between the first and second harmonics, typical of ${\chi }^{\left(2\right)}$ microresonators, and to the presence of the pump. They have no zero-pump counterparts relevant to conservative solitons. The stability issue for the found comb solutions remains open and requires further numerical analysis.

We consider the quantum traversal time of an incident wave packet across a potential well using the theory of quantum time of arrival (TOA) operators. This is done by constructing the corresponding TOA operator across a potential well via quantization. The expectation value of the potential-well TOA operator is compared to the free-particle case for the same incident wave packet. The comparison yields a closed-form expression of the quantum well traversal time which explicitly shows the classical contributions of the positive and negative momentum components of the incident wave packet and a purely quantum-mechanical contribution significantly dependent on the well depth. An incident Gaussian wave packet is then used as an example. It is shown that for shallow potential wells, the quantum well traversal time approaches the classical traversal time across the well region when the incident wave packet is spatially broad and approaches the expected quantum free-particle traversal time when the wave packet is localized. For deep potential wells, the quantum traversal time oscillates from positive to negative, implying that the wave packet can be advanced or delayed.

We reconstruct finite-dimensional quantum theory with superselection rules, which can describe hybrid quantum-classical systems, from four purely operational postulates: symmetric sharpness, complete mixing, filtering, and local equality. It has been shown that each of the classical and fully quantum theories is singled out by an additional postulate.

S-money [A. Kent, Proc. R. Soc. A 475, 20190170 (2019)] schemes define virtual tokens designed for networks with relativistic or other trusted signaling constraints. The tokens allow near-instant verification and guarantee unforgeability without requiring quantum state storage. We present refined two stage S-money schemes. The first stage, which may involve quantum information exchange, generates private user token data. In the second stage, which need only involve classical communications, users determine the valid presentation point, without revealing it to the issuer. This refinement allows the user to determine the presentation point anywhere in the causal past of all valid presentation points. It also allows flexible transfer of tokens among users without compromising user privacy.

The scale-free property emerges in various real-world networks and is an essential property that characterizes the dynamics or features of such networks. In this work, we investigate the effect of this scale-free property on a quantum information processing task of finding a marked node in the network, known as the quantum spatial search. We analyze the quantum spatial search algorithm using a continuous-time quantum walk on the Bollobás network, and we evaluate the time $T$ to localize the quantum walker on the marked node starting from an unbiased initial state. Our main finding is that $T$ is determined by the global structure around the marked node, while some local information of the marked node, such as the degree, does not identify $T$. We discuss this by examining the correlation between $T$ and some centrality measures of the network, and we show that the closeness centrality of the marked node is highly correlated with $T$. We also characterize the distribution of $T$ by marking different nodes in the network, which displays a multimode log-normal distribution. Especially on the Bollobás network, $T$ is a few orders of magnitude shorter depending on whether the marked node is adjacent to the largest degree hub node. However, as $T$ depends on the property of the marked node, one requires some amount of prior knowledge about such a property of the marked node in order to identify the optimal time to measure the quantum walker and achieve a fast search. These results indicate that the existence of the hub node in the scale-free network plays a crucial role in the quantum spatial search.

As an essential quantum resource in quantum information processing, entanglement between macroscopic systems has been applied to both quantum technologies and foundational studies of the boundary between the quantum and classical worlds. Inspired by the proposal by Li et al. [Phys. Rev. Lett. 117, 015502 (2016)], we propose a scheme that is composed of two separated nitrogen-vacancy centers coupled to the vibration mode of a nanotube for creating entanglement between the two ensembles. An approximate analytical solution related to the calculation of macroscopic entanglement for this two-spin-ensemble model is derived. This kind of analytical solution will be crucial for directly testing the contribution of the experimental parameters, especially for the calculation of macroscopic entanglement in follow-up work. Including the dephasing and mechanical dissipation, we show that two spin ensembles are entangled with time evolution under realistic experimental conditions. This macroscopic entanglement is applicable for applied ideas related to quantum computation and communication, as well as the studies of the boundary between quantum and classical worlds. Moreover, we describe how to realize this practical model and demonstrate this macroscopic entanglement in experiments.