We study collisions between a ferrodark soliton (FDS) and an antiFDS (${\mathbb{Z}}_2$ kinks in the spin order) in the easy-plane phase of spin-1 Bose-Einstein condensates (BECs). For a type-I pair (type-I FDS-antiFDS pair) at low incoming velocities, the pair annihilates followed by the formation of an extremely long-lived dissipative breather on a stable background, a spatially localized wave packet with out-of-phase oscillating magnetization and mass superfluid densities. Periodic emissions of spin and density waves cause breather energy dissipation and we find that the breather energy decays logarithmically in time. When the incoming velocity is larger than a critical velocity at which a stationary FDS-antiFDS pair forms, a pair with finite separating velocity is reproduced. When approaching the critical velocity from below, we find that the lifetime of the stationary type-I pair shows a power-law divergence, resembling a critical behavior. In contrast, a type-II pair (type-II FDS-antiFDS pair) never annihilates and only exhibits reflection. For collisions of a mixed type FDS-antiFDS pair, as ${\mathbb{Z}}_2$ kinks in the spin order, reflection occurs in the topological structure of the magnetization while the mass superfluid density profiles pass through each other, manifesting spin-mass separation.

Nonreciprocity enables unidirectional energy transfer that facilitates development of quantum devices with high efficiency, strong robustness, and advanced functionalities. For light-matter interaction, the implementation of nonreciprocity is limited by the fundamental principle of time-reversal symmetry in electromagnetics. Here we demonstrate that the nonreciprocal light-matter interaction can be realized at the single-photon level between a linearly polarized quantum emitter (QE) and two degenerate whispering gallery modes of hybrid plasmonic-photonic cavity featuring chiral exceptional points (EPs). This tripartite nonreciprocal interaction results from the chiral energy flow created by balancing the coherent and dissipative couplings: The destructive interference of the plasmon-mediated dissipative interaction and its coherent counterpart give rise to unidirectional coupling between the QE and cavity modes, while the unidirectional coupling between two cavity modes is achieved by the destructive interference of dissipative interactions induced by plasmon and chiral EPs, where the phase of light emerges as an additional degree of freedom to flexibly tune the coupling coefficient in a complex space. Controlling the direction of chiral energy flow through the destructive interference of coherent and dissipative couplings results in nonreciprocal QE-cavity interaction, which is evidenced by the population dynamics with different configurations of initial excitation. As a quantum-optics application, we show that the established nonreciprocity enables the proposed hybrid cavity to serve as a multiplexing quantum light source for single photons and two photons generated in the traveling-wave modes with opposite propagating directions. Our results provide a feasible scheme for the experimental realization of nonreciprocal light-matter interaction in nanophotonic systems, which holds great potential in building nonreciprocal quantum devices for future applications in quantum computing and quantum information processing.

Extending classical synchronization to the quantum domain is of great interest both from the fundamental physics point of view and with a view toward quantum technology applications. This work characterizes phase synchronization of an effective spin-1 system, which is realized by coupling three quantum states with infinite lifetime to auxiliary excited states that have a finite lifetime. Integrating out the excited states, the effective spin-1 model features coherent and incoherent effective couplings. The following are our key findings. (i) Phase synchronization can be controlled by adjusting the phases of the couplings to the excited states. (ii) Unlike in the paradigmatic spin-1 system studied in the literature, where the dissipative couplings describe decay into the limit-cycle state, the effective spin-1 model investigated in this work is governed by a competition between dissipative decay into and out of the limit-cycle state, with the dissipative decay out of the limit-cycle state playing a critical role. (iii) We identify a parameter regime where phase synchronization of the effective spin-1 system is, in the absence of coherent effective couplings, governed entirely by the effective dissipators. The effective spin-1 model is benchmarked through comparisons with master-equation calculations for the full Hilbert space. Physical insights are gained through analytical perturbation theory calculations. Our findings, which are expected to hold for a broad class of energy-level and coupling schemes, are examined using hyperfine states of ${}^{87}\mathrm{Rb}$ as an example system.

Topological boundary states exhibit distinctive properties, including unidirectional propagation and noise robustness, which hold significant potential for advancing the performance of quantum science and technology. Here, we demonstrate the implementation of non-Abelian quantum interference and entanglement generation, protected by dual symmetries (time-independent inversion and time-dependent interchain), in coupled Su-Schrieffer-Heeger chains. Specifically, in a multichain system, we first achieve tunable topological transfer of a single particle, where the destination chain is selected by the permutation sequence. We then extend this to two particles, observing a non-Abelian Hong-Ou-Mandel interference that generates spatially entangled NOON states whose properties are dictated by the permutation sequence. Our work establishes an alternative pathway for exploring non-Abelian topology applied to quantum science and technology, enabled by the unique protection of time-dependent symmetry.

We analyze quantum metrological protocols, where the sensing system is linearly coupled to a bosonic environment, by performing a Markovian embedding of the problem based on pseudomode formalism. This allows us to effectively model the problem using low-dimensional environment and apply recently developed powerful tools that yield optimal metrological protocols and fundamental metrological bounds for correlated-noise models. We illustrate the method by investigating a frequency estimation protocol in the presence of noise modeled effectively as a damped Jaynes-Cummings dynamics.

Quantum neural networks employ parametrized quantum circuits (PQCs) to map data inputs to desired predictions. Recent analytical research demonstrates that PQCs consisting of data reuploading structure are naturally expressed as partial Fourier series and that a single-qubit circuit can serve as a universal approximator for univariate functions. However, this prior work largely focuses on representational capacity and does not provide intuitive or structural explanations of how the individual circuit components govern the resulting Fourier coefficients. In this paper, we peel back the black box and analyze the intrinsic structure of PQCs. In particular, we investigate how data encoding, repeated reuploading, and trainable unitary operators combine to represent function classes characterized by a Fourier expansion with specific accessible frequency components. Our key contribution is to show, both mathematically and empirically, that the configuration of trainable parameters creates an output qubit trajectory that is critical for the representation of Fourier coefficients. We further introduce a strategy for designing a data encoder with tunable scaler, which ensures that the circuit generalizes its mapping ability to capture a target frequency spectrum of the input data.

In resource-efficient near-term quantum computers, development on the variational quantum eigensolver (VQE) algorithm that improves the accuracy of electronic structure calculations while maintaining low-requirement quantum gate counts is indispensable. We integrate Slater-type orbitals within the VQE framework, where the ground-state energy minimization with respect to the Slater exponents is shown as a second-order dependence on these parameters, enhancing accuracy compared with the standard methods while maintaining the same number of qubits. Using the full configuration interaction energy as the cost function, optimized parameters for first- and second-row elements are reported and related to the shielding constant, indicating a need to revise the previously established Slater rules. The active space is improved by substantially contracting the orbital exponents of extended basis sets relative to minimal ones, hence capturing additional electron-correlation effects. By considering the geometric structure of the parameter space, quantum Slater-exponent optimization (Q-SEO) demonstrates accelerated convergence to the target ground state, characterized by distinct parameter trajectories. The integration of a decision tree with Q-SEO effectively mitigates error in noisy environments.

Charge exchange spectroscopy is carried out in collisions of He-like ${\mathrm{C}}^{4+}$, ${\mathrm{N}}^{5+}$, and ${\mathrm{O}}^{6+}$ ions with He at a collision energy of approximately 5 keV/u, and emissions from ${\mathrm{He}}^{+}$ are observed in the extreme ultraviolet and visible spectral regions. We report emission cross sections for transfer excitation (TE) of ${\mathrm{He}}^{+}$ in these collision systems and discuss the angular momentum distribution among the population of excited ${\mathrm{He}}^{+}$ states. The optical sensitivity is calibrated by comparing the theoretically calculated emission intensities with the measured spectra. The pattern of observed and unobserved transitions indicates that TE preferentially populates high angular momentum states in ${\mathrm{He}}^{+}$. Furthermore, analysis based on the potential curve-crossing model suggests that single-electron capture plays a more significant role in TE than double-electron capture.

We present ab initio calculations of the static and dynamic electric dipole polarizability of the barium monohydroxide (${}^{138}\mathrm{BaOH}$) molecule, using relativistic coupled-cluster theory. By thoroughly investigating the dependence of the calculated polarizabilities on computational parameters (basis set size, treatment of relativistic and QED effects, level of description of electron correlation, and vibrational corrections), a procedure for determining uncertainties is constructed and applied. The electric dipole moment of BaOH is also calculated and compared to experiment. The static and dynamic (for $\lambda =1064\text{nm}$) polarizability tensor elements were calculated within the electronic ground state for both the (000) vibrational ground state and the (010) bending vibrationally excited state, the latter state being particularly interesting for a wide range of quantum experiments. The ground-state static polarizability tensor elements are calculated to be 200.8(24) a.u. and 297(5) a.u. for the parallel and perpendicular components, respectively.

The static and dynamic electric dipole polarizabilities of the $5s^2{}^{1}S_0$ and $5s5p{}^{3}P_{0,2}$ states of Sr atoms are calculated using the relativistic configuration interaction plus the many-body perturbation theory (RCI + MBPT) method. Magic wavelengths are determined for the transitions $5s^2{}^{1}S_0\to 5s5p{}^{3}P_0$, $5s^2{}^{1}S_0\to 5s5p{}^{3}P_2$, and $5s5p{}^{3}P_0\to 5s5p{}^{3}P_2$. A comprehensive study is conducted on the dependence of magic wavelengths on the angle between the laser polarization and the magnetic field. Furthermore, the conditions for realizing triple magic trapping at 813.4 nm for the $5s^2{}^{1}S_0$, $5s5p{}^{3}P_0$, and $5s5p{}^{3}P_2$ states are investigated. In the case of linearly polarized light, when the angle (${\theta }_p$) between the laser polarization direction and the magnetic field is $79.1{\left(0.7\right)}^{\circ }$, triple magic trapping for the $5s^2{}^{1}S_0$, $5s5p{}^{3}P_0$, and $5s5p{}^{3}P_{2}M=0$ states can be achieved. This result agrees well with the recent experimental measurement $(78.49{\left(3\right)}^{\circ }$)[M. Ammenwerth et al., Phys. Rev. Lett. 135, 143401 (2025)]. Meanwhile, triple magic trapping involving the $5s5p{}^{3}P_{2}M=2$ state can be achieved when ${\theta }_p=37.4{\left(0.3\right)}^{\circ }$. The conditions for achieving triple magic trapping with circularly and arbitrarily elliptically polarized light are also presented.

We determine with high accuracy the energy of the inner-shell transition $1s^{2}2s^2{}^{1}S_0\to 1s2s^{2}2p_{3/2}{}^{1}P_1{}^{16}\mathrm{O}_{K\alpha }^{4+}$ at 554.372(3) eV ($\lambda =22.36480\left(12\right)\AA$) as well as its small shift of $2.2\pm 1.3$ meV ($\mathrm{\Delta }\lambda =0.089\left(52\right)\mathrm{m}\AA$) for the ${}^{18}\mathrm{O}$ isotope. This transition blends with a $K\alpha$ line of ${\mathrm{O}}^{5+}$ used in astrophysical diagnostics, potentially affecting its reliability. In contrast to our experimental uncertainty of $\pm 3$ meV, advanced electronic structure predictions for this four-electron system, including quantum electrodynamic (QED) corrections on the order of 100 meV, still scatter by more than $\pm 250$ meV. Ions generated and stored in an electron beam ion trap were excited at the ELETTRA synchrotron facility with monochromatic soft x rays, with photon energies corrected by an additional spectrometer. Upon resonant excitation of ${\mathrm{O}}^{4+}$ and their subsequent autoionization, we separate the photoions of each isotope by a time-of-flight measurement. This way, we resolve soft x-ray isotopic shifts of a few meV, obtain very accurate data on essential astrophysical ions, and test calculations down to the level of QED contributions.

We investigate the generation of spatially resolved, elliptically polarized high-order harmonics in argon gas, driven by a two-dimensional laser field, using extended macroscopic propagation theory. By only varying the gas pressure while keeping other parameters fixed, the intense cutoff harmonics exhibit a high degree of circular polarization (DCP) and are spatially separated from the lower-order harmonics at the gas-medium exit under the optimal condition. For different harmonic orders, we demonstrate that the spatial distributions of harmonic intensity, DCP, and emission angle within the gas medium, as well as the absorption length, differ significantly, while the electron trajectories and DCP in the single-atom response also vary markedly, accounting for the observed harmonic features under phase-matching conditions. We further examine dependence of the spatial features of elliptically polarized high-order harmonic generation (HHG) on gas pressure. Finally, we present far-field spatial profiles of cutoff harmonics with large DCP values, which become increasingly separated from the driving laser field at higher gas pressures, forming an annular harmonic beam with a divergence angle of 5 mrad. This work provides a theoretical foundation for understanding and optimizing elliptically polarized HHG in atoms.

Rydberg state excitation is an elusive strong-field phenomenon characterized by tunneling of bound electrons without subsequent ionization. Here, investigating theoretically the pulse duration dependence of the modulation of excitation probability versus laser intensity, we unravel the excitation dynamics of electrons driven by an intense laser pulse in the subcycle scale. It is shown that as a consequence of interference between electron wave packets emitted at different times during the capture process, the positions of peaks in the excitation probability of individual excited states critically depend on the types of interference. Specifically, intracycle interference leads to an intensity spacing of approximately $52{\mathrm{TW}/\mathrm{cm}}^2$ for an 800 nm wavelength, which depends on the parity of the excited states, whereas intercycle interference produces a spacing of about $26{\mathrm{TW}/\mathrm{cm}}^2$ and is parity independent. This interference behavior accounts for the strong pulse-duration dependence observed in the modulation of excitation probabilities. Furthermore, we elucidate the physical mechanism underlying the irregular excitation probability patterns that emerge for longer pulse durations. Beyond prior works, our results establish a unified physical picture explaining the distinct multipeak structures observed in both ionization and excitation phenomena, thereby advancing a comprehensive understanding of strong-field electron dynamics.

We study a transversely pumped atomic Bose-Einstein condensate coupled to a single-mode optical cavity, where effective atom-atom interactions are mediated by pump and cavity photons. A number of experiments and theoretical works have shown the formation of a superradiant state in this setup, where interference of pump and cavity light leads to an optical lattice in which atoms self-consistently organize. This self-organization has been extensively studied using the approximate Dicke model (truncating to two momentum states), as well as through numerical Gross-Pitaevskii simulations in one and two dimensions. Here, we perform a full mean-field analysis of the system, including all relevant atomic momentum states and the cavity field. We map out the steady-state phase diagram vs pump strength and cavity detuning, and provide an in-depth understanding of the instabilities that are linked to the emergence of spatiotemporal patterns. We find and describe parameter regimes where the mean field predicts bistability, regimes where the dynamics form chaotic trajectories, instabilities caused by resonances between normal mode excitations, and states with atomic dynamics but vanishing cavity field.

This study investigates the role of Einstein-Podolsky-Rosen steering in characterizing the energy dynamics of quantum batteries (QBs) within a charging system that features shared reservoirs. After optimizing parameter configurations to achieve high-energy systems, we observe that steering serves as a vital resource across a variety of charging scenarios with low-dissipation regimes: it is initially stored until the system reaches energy equilibrium, and then subsequently utilized to sustain the enhancement of energy storage. Furthermore, steering acts as a witness to battery population balance and a consumable that enhances extractable work. Additionally, we discuss the contribution of the steering potential to energy upon high-dissipation charging in detail. These findings establish an indicator for monitoring QB energy variations, which will be beneficial to achieve the high-performance quantum batteries.

Photonic crystal waveguides (PCWs) allow for the engineering of photonic waveguide modes and band structures to control the flow of light and enhance light-matter interactions within the waveguide. They have shown potential for enhancing optical nonlinearities, single photon emissions from quantum dots, as well as for use in optical buffers due to their ability to confine fields on-chip and produce slow-light modes. While these features are promising for applications in nanophotonics, PCWs are prone to high scattering losses due to disorder-induced backscattering, which has remained a major challenge across various waveguide designs for decades. By combining a fast mode solving approach with physics-based scattering formulas and inverse design, we show how backscattering losses can be significantly reduced, even when working at the same group index. We demonstrate substantial improvements for both W1-like waveguide modes and topological waveguide modes. Our general methodology is fully three-dimensional and can be used to design new PCWs optimized for a variety of performance metrics.

Goos-Hänchen (GH) shifts are theoretically investigated in parity-time ($\mathcal{PT}$)-symmetric photonic crystals with a Weyl semimetal (WSM) defect layer at the center. The transmission spectrum features a sharp Fano resonance coupled with a laser point, both originating from the epsilon near zero response. Remarkably, giant quasireciprocal GH shifts up to $3.28\times {10}^4\lambda$ are achieved at the Fano resonance frequency, despite the system's overall nonreciprocal reflectance characteristics. The coincidence of the Fano resonance and laser point makes the corresponding reflectance of the GH shift high enough to be detected. These GH shifts demonstrate strong dependence on incidence angle (θ) and gain-loss factor ($q$) while maintaining a fixed operational wavelength. Notably, abrupt negative-to-positive inversions of the GH shifts occur at critical values of θ and $q$, with a small distinct nonreciprocal regime. The GH shifts can be further tuned by increasing the WSM's Fermi energy ($E_f$), enhancing both the GH shift magnitude and its operational frequency. Elevating temperatures ($T$) reduce the shift magnitude and induce a blueshift. Additionally, these phenomena are unique to the two-Weyl-node configuration—no comparable Fano resonance or GH shifts appear for systems with additional Weyl nodes. The exceptional sensitivities of these GH shifts to θ, $q, E_f$, and $T$ suggest promising applications in optical switching, precision sensing, and quasireciprocal photonic devices.

Tunable mode-locked fiber lasers have attracted significant attention for their ability to generate ultrashort pulses with flexible wavelength control. Here, we present the experimental demonstration of a fully fiber-integrated, reversibly tunable wavelength technology in the $C$ band controlled solely by pump power regulation, achieving a continuous wavelength tuning range of 19.2 nm through pump power adjustment. To the best of our knowledge, this work demonstrates the widest continuous wavelength tuning range via pump power regulation in a fully fiber-integrated system. The pump-power-dependent wavelength tuning is due to the interaction of self-phase modulation, constant phase shift satisfying the nonlinear polarization rotation phase-matching condition, and the gain spectrum filtering effect. With the gradual increase of pump power, a controlled blueshift of the soliton central wavelength is observed, and the tuning process proves to be reversible. Notably, no soliton splitting occurred despite the continuous elevation of the pump power. Benefiting from its simple tuning mechanism, stable output, and preserved soliton type, the proposed laser provides a robust platform for future applications in sensing, spectroscopy, and biomedical imaging.

We develop a model for non-Gaussian state generation via spontaneous parametric down-conversion (SPDC) in InGaP microring resonators. The nonlinear Hamiltonian is written in terms of the asymptotic fields for the system, which includes a phantom channel to handle scattering loss. The full ket for the system is written as a Gaussian unitary acting on a residual non-Gaussian ket, which is vacuum initially and evolves according to a non-Gaussian Hamiltonian. We show that for realistic parameters we can access the pump depletion regime, where the Wigner function for the residual non-Gaussian ket has negativity. But we find that the non-Gaussian features for the full ket could be unobservable due to the large amount of squeezing required to lead to pump depletion. We show that a potential solution in the low-loss regime is to implement an inverse Gaussian unitary on the accessible modes to remove most of the squeezing and reveal the non-Gaussian features. This work provides a foundation for modeling pump-depleted SPDC in integrated lossy microring resonators, opening a path toward a scalable on-chip non-Gaussian source.