Modern applications of atomic physics, including the determination of frequency standards and the analysis of astrophysical spectra, require prediction of atomic properties with exquisite accuracy. For complex atomic systems, high-precision calculations are a major challenge due to the exponential scaling of the involved electronic configuration sets. This exacerbates the problem of required computational resources for these computations and makes indispensable the development of approaches to select the most important configurations out of otherwise intractably huge sets. We have developed a neural-network (NN) tool for running high-precision atomic configuration interaction (CI) computations with iterative selection of the most important configurations. Integrated with the established pCI atomic codes, our approach results in computations with significantly reduced computational requirements in comparison with those without NN support. We showcase a number of NN-supported computations for the energy levels of ${\mathrm{Fe}}^{16+}$ and ${\mathrm{Ni}}^{12+}$ and demonstrate that our approach can be reliably used and automated for solving specific computational problems for a wide variety of systems.

The effect of impenetrable confinement has been rigorously tested on the information-theoretic measures of Shannon information entropy, Fisher measure, Onicescu energy, and entanglement measures, such as von Neumann and linear entropy, corresponding to ${\mathrm{H}}^{-}$, He, and ${\mathrm{Li}}^{+}$ in their ground electronic state. High-quality variational Hylleraas-like expansion as well as the accurate numerical Hartree-Fock wave functions have been employed for the chosen set of two-electron $Zee$ systems. The impenetrable confinement has been mimicked with a spherical cavity model potential of varying radius $R$, which in turn, is used to quantify thermodynamic pressure within the adiabatic approximation. The structural properties such as total energy, energy components, and geometrical properties (expectation values electron-electron separation and electron-nuclear distance) have been estimated to test the accuracy and viability of the present calculation. Some intriguing scaling laws related to von Neumann, linear, and Shannon entropy as a function of pressure are proposed. The influence of impenetrable confinement on the transition probability of He $\to {\mathrm{Li}}^{+}$ during nuclear $\beta$ decay is quantitatively assessed.

The recent experimental realization of clock-laser-induced synthetic gauge fields and one-dimensional spin-orbit coupling in ultracold alkaline-earth(-like) atoms provides a new way to explore topological quantum states with suppressed heating effects. Here, we propose a scheme for realizing a synthetic quantum Hall tube and ribbon in an optical lattice clock system with multiple optical clock transition couplings. The legs of the synthetic Hall system are composed of the atomic ground and metastable orbital states, and the couplings between the legs are generated by clock lasers, resulting in a synthetic gauge flux. We investigate the band structure and topological phase diagram under various conditions and demonstrate the phase transition. The momentum-resolved quench dynamics of the synthetic Hall system is analyzed to demonstrate the presence of gauge flux on plaquettes and reveal the critical point of the phase transition. The hyperfine spin can serve as an additional synthetic dimension, allowing a two-component Hall system to be realized in synthetic dimensions. A size-enlarged Hall system could be realized by coupling the magnetic sublevels and orbital states simultaneously. Our scheme is within reach of existing optical lattice clocks and thus provides a realistic method to achieve topological quantum Hall systems with ultracold alkaline-earth(-like) atoms. This study paves the way for realizing quantum spin Hall states with hyperfine spins and has the potential to explore more interesting topological phases.

We introduce a hybrid optomechanical system containing an annularly trapped Bose-Einstein condensate (BEC) inside an optical cavity driven by Lauguerre-Gaussian (LG) modes. Spiral phase elements serve as the end mirrors of the cavity such that the rear mirror oscillates torsionally about the cavity axis through a clamped support. As described earlier in a related system [P. Kumar et al., Phys. Rev. Lett. 127, 113601 (2021)], the condensate atoms interact with the optical cavity modes carrying orbital angular momentum which create two atomic side modes. We observe three peaks in the output noise spectrum corresponding to the atomic side modes and rotating mirror frequencies, respectively. We find that the trapped BEC's rotation reduces quantum fluctuations at the mirror's resonance frequency. We also find that the atomic side modes-cavity coupling and the optorotational coupling can produce bipartite and tripartite entanglements between various constituents of our hybrid system. We reduce the frequency difference between the side modes and the mirror by tuning the drive field's topological charge and the condensate atoms' rotation. When the atomic side modes become degenerate with the mirror, the stationary entanglement between the cavity and the mirror mode diminishes due to the suppression of cooling. Our proposal, which combines atomic superfluid circulation with mechanical rotation, provides a versatile platform for reducing quantum fluctuations and producing macroscopic entanglement with experimentally realizable parameters.

Spontaneous symmetry breaking (SSB) occurs when modes of asymmetric profile appear in a symmetric, double-well potential, due to the nonlinearity of the potential exceeding a critical value. In this study, we examine SSB in a periodic potential where the unit cell itself is a symmetric double well, in both one-dimensional (1D) and two-dimensional (2D) periodic systems. Using the tight-binding model, we derive the analytical form that predicts the critical power at which SSB occurs for both 1D and 2D systems. The results show that the critical power depends significantly on the quasimomentum of the Bloch mode, and as the modulus of momentum increases, the SSB threshold decreases rapidly, potentially dropping to zero. These analytical findings are supported by numerical nonlinear eigenmode analysis and direct propagation simulations of Bloch modes.

Out-of-equilibrium driven nonlinear oscillators have attracted interest as a platform for tailoring Floquet Hamiltonian spectra and stabilizing quantum states for quantum information. However, it is usually ignored that the necessary parametric drive can amplify environmental fluctuations limiting applications. In this work, we capture this effect by computing the effective Lindbladian of a Kerr parametric oscillator beyond the rotating wave approximation. We find that the relevant dissipators depend strongly on the nonlinearity and the mean-photon number in the oscillator. In particular, we address recent measurements of the logical lifetime on a Schrödinger's-cat qubit stabilized by a parametric drive, thereby providing an explanation for the observed three-order-of-magnitude discrepancy between experimental data and an ordinary Lindblad treatment. Our systematic approach paves the path to treat dissipative effects in Floquet-engineered nonlinear quantum systems.

In recent years, the detection of genuine multipartite entanglement (GME) via machine learning has received scant attention. Here, we employ convolutional neural networks (CNNs), as well as CNNs enhanced with squeeze and excitation (SE) to detect GME. We randomly generated GME states with 4 to 6 qubits and GHZ-diagonal states ranging from 4 to 20 qubits using the semidefinite programming approach. Subsequently, we assessed their classification accuracy. Our results demonstrate that the integration of the SE module significantly improved training performance. Additionally, we conducted an analysis of false positive and false negative occurrences. Utilizing our training data, we have substantially reduced the likelihood of incorrectly classifying nonentangled states as entangled.

The concept of wave-particle duality holds significant importance in the field of quantum mechanics, as it elucidates the dual nature encompassing both wavelike and particlelike properties exhibited by microscopic particles. In this paper, we construct generalized measures for the predictability and visibility of $n$-path interference fringes to quantify the wave and particle properties in quantum high-dimensional systems. By employing the Morozova-Chentsov function, we ascertain that the wave-particle relationship can be delineated by the average coherence. This function exhibits a close correlation with the metric-adjusted skew information, thereby we establish complementary relations between visibility, predictability, and quantum $f$ entropy, which reveal deep connections between wave-particle duality and other physical quantities. Through our methodology, diverse functions can be selected to yield corresponding complementary relationships.

Time-bin entanglement is a critical resource in quantum information science owing to its exceptional robustness over long-distance channels. Achieving high quantum interference visibility is indispensable for fundamental research and practical applications. To date, a model that can accurately describe time-bin entanglement-based two-photon interference remains to be established. In this work, we analyze the underlying mechanisms for this type of interference and develop an effective model for experimentally optimizing the quantum interference visibility. We use this model to analyze the factors contributing to the decline in interference visibility and offer strategies to address these issues, and we also demonstrate its effectiveness through experiments. Our model can serve as a tool for time-bin entanglement-based systems, aiding in system design, the evaluation of expected outcomes, and the optimization of experimental setups.

In this paper we use a variational quantum algorithm to solve initial value problems with the implicit Crank-Nicolson and the method of lines (MoL) evolution schemes. The unknown functions use a spectral decomposition with the Fourier basis. The examples developed to illustrate the implementation are the advection equation, the wave equation written as a system of first-order coupled equations, and the viscous Burgers equation as a nonlinear case. The problems are solved using (i) standard finite differences as the solution to compare with, (ii) the state vector formalism (SVF), and (iii) the sampling error formalism (SEF). The contributions of this paper include (1) cost functions for generic first order in time partial differential equations (PDEs) using the implicit Crank-Nicholson and the MoL, (2) detailed convergence or self-convergence tests are presented for all the equations solved, (3) a system of three coupled PDEs is solved, (4) solutions using sampling error are presented, which highlights the importance of simulating the sampling process, and (5) a fast version of the SVF and SEF was developed which can be used to test different optimizers faster.

We study the performance of an Ising spin network for quantum reservoir computing in linear and nonlinear memory tasks. We investigate the extent to which quantumness enhances performance by monitoring the behavior of quantum entanglement, which we quantify by the partial transpose of the density matrix. In the most general case where the effects of dissipation are incorporated, our results indicate that the strength of the entanglement advantage depends on the frequency of the input signal; the benefit of entanglement is greater with more rapidly fluctuating signals, whereas a low-frequency input is better suited to a nonentangled reservoir. This may be understood as a condition for an entanglement advantage to manifest itself: the system's quantum memory must survive long enough for the temporal structure of the input signal to reveal itself. We also find that quantum entanglement empowers a spin-network quantum reservoir to remember a greater number of temporal features.

A quantum particle evolving by Schrödinger's equation in discrete space constitutes a continuous-time quantum walk on a graph of vertices and edges. When a vertex is marked by an oracle, the quantum walk effects a quantum search algorithm. Previous investigations of this quantum search algorithm on graphs with cliques have shown that the edges between the cliques can be weighted to enhance the movement of probability between the cliques to reach the marked vertex. In this paper, we explore the most restrictive form of this by analyzing search on a weighted barbell graph that consists of two cliques of the same size joined by a single weighted edge or bridge. This graph is generally irregular, so quantum walks governed by the graph Laplacian or by the adjacency matrix can differ. We show that the Laplacian quantum walk's behavior does not change, no matter the weight of the bridge, and so the single bridge is too restrictive to affect the walk. Similarly, the adjacency quantum walk's behavior is unchanged for most weights, but when the weight equals the size of a clique, the probability does collect at the clique containing the marked vertex, and utilizing a two-stage algorithm with different weights for each stage, the success probability is boosted from 0.5 to 0.996, independent of the size of the barbell graph.

Utilizing the Stern-Gerlach apparatus to create matter-wave superposition states is a long-sought-after goal, not only due to its potential applications in the quantum realm, but also because of its fundamental implications for studying the quantum properties of gravity. The main challenge in creating a macroscopic quantum interferometer arises from the loss of coherence, primarily through two channels. One channel involves strong coupling with the environment for macroscopic matter, leading to decoherence. The other channel relates to the precision of wave-packet overlap, which can occur due to external and internal fluctuations of various sources. The latter introduces a unique challenge for larger-scale masses by perturbing the center of mass motion of the macroscopic object. Here we study a particular challenge, namely, the issue of internal degrees of freedom, specifically phonon fluctuations and contrast reduction. This work investigates the contrast reduction caused by spin–magnetic-field–phonon and diamagnetism-phonon interactions in the quantum gravity-induced entanglement of masses protocol configuration.

We demonstrate theoretically that waveguide-coupled cavities with embedded two-level emitters can act as a highly efficient, high-fidelity single-photon switch. The photon switch is an optical router triggered by a classical signal—the propagation direction of single input photons in the waveguide is controlled by changing the emitter-cavity coupling parameters in situ, for example, using applied fields. The switch reflects photons in the weak emitter-cavity coupling regime and transmits photons in the strong coupling regime. By calculating transmission and reflection spectra using the input-output formalism of quantum optics and the transfer matrix approach, we obtain the fidelity and efficiency of the switch with a single-photon input in both regimes. We find that a single waveguide-coupled cavity can route input photon wave packets with near-unity efficiency and fidelity if the wave packet width is smaller than the cavity mode linewidth. We also find that using multiple waveguide-coupled cavities increases the switching bandwidth, allowing wider wave packets to be routed with high efficiency and fidelity. For example, an array of three waveguide-coupled cavities can reflect an input Gaussian wave packet with a full width at half-maximum of 1 nm (corresponding to a few-picosecond pulse) with an efficiency $E_r=96.4\%$ and a fidelity $F_r=97.7\%$, or transmit the wave packet with an efficiency $E_t=99.7\%$ and a fidelity $F_t=99.8\%$. Such efficient, high-fidelity single-photon routing is essential for scalable photonic quantum technologies.

We develop a quantum topological data analysis (QTDA) protocol based on the estimation of the density of states (DOS) of the combinatorial Laplacian. Computing topological features of graphs and simplicial complexes is crucial for analyzing data sets and building explainable artificial intelligence solutions. This task becomes computationally hard for simplicial complexes with over 60 vertices and high-degree topological features due to a combinatorial scaling. We propose to approach the task by embedding underlying hypergraphs as effective quantum Hamiltonians and evaluating their density of states from the time evolution. Specifically, we compose propagators as quantum circuits using the Cartan decomposition of effective Hamiltonians and sample overlaps of time-evolved states using multifidelity protocols. Next we develop various postprocessing routines and implement a Fourier-like transform to recover the rank (and kernel) of Hamiltonians. This enables us to estimate the Betti numbers, revealing the topological features of simplicial complexes. We test our protocol on noiseless and noisy quantum simulators and run examples on IBM quantum processors. We observe the resilience of the proposed QTDA approach to real-hardware noise even in the absence of error mitigation, showing the promise for near-term device implementations and highlighting the utility of global DOS-based estimators.

The possibility that one party steers their partner is discussed for a driven two-qubit system, where it is assumed that either one or both of them is driving via an exponential pulse. It is shown that the maximum and minimum degrees of steerability and the survival amount of quantum correlation depend on the initial-state settings and the pulsing strength. If only one party is driven, the long-lived steerability is observed at long pulsing time and high strength. However, if both parties are driven, then the steerability's behavior depends on the difference between the strengths of the pulses.

We provide a measurement of the $6s6p{}^{3}P_0–5d6s{}^{3}D_1$ transition in multiple isotopes of ytterbium (Yb) at 1389 nm. We measure the absolute frequencies of ${}^{170}\mathrm{Yb}$, ${}^{171}\mathrm{Yb}$ (1/2–1/2), ${}^{171}\mathrm{Yb}$ (1/2–3/2), ${}^{172}\mathrm{Yb}$, ${}^{173}\mathrm{Yb}$ (5/2–3/2), ${}^{173}\mathrm{Yb}$ (5/2–5/2), ${}^{173}\mathrm{Yb}$ (5/2–7/2), ${}^{174}\mathrm{Yb}$, ${}^{176}\mathrm{Yb}$ $6s6p{}^{3}P_0–5d6s{}^{3}D_1$ transitions with modulation transfer spectroscopy (MTS) in a hollow cathode lamp. High-resolution dispersive signals of the MTS are obtained for all the stable isotopes, except for low-abundance ${}^{168}\mathrm{Yb}$. The frequencies of these transitions are measured from the beat signals between a stabilized optical frequency comb and the MTS-locked laser, and the systematic shifts therein are corrected. The hyperfine components ${}^{173}\mathrm{Yb}$ (5/2–5/2) and ${}^{171}\mathrm{Yb}$ (1/2–3/2) of the $6s6p{}^{3}P_0–5d6s{}^{3}D_1$ transition for ${}^{173}\mathrm{Yb}$ and ${}^{171}\mathrm{Yb}$ isotopes overlap to form an overlapped line; we determine their frequencies by a fitting method. The isotope shifts relative to ${}^{174}\mathrm{Yb}$ are determined as 284.5(20) MHz for ${}^{170}\mathrm{Yb}$, 121.5(7) MHz for ${}^{172}\mathrm{Yb}$ and −114.6(6) MHz for ${}^{176}\mathrm{Yb}$. The hyperfine constants of the $5d6s{}^{3}D_1$ state are determined as $A\left({}^{171}\mathrm{Yb}\right)=-2039.4\left(7\right)\mathrm{MHz}$, $A\left({}^{173}\mathrm{Yb}\right)=563.5\left(2\right)\mathrm{MHz}$, and $B\left({}^{173}\mathrm{Yb}\right)=336.8\left(3\right)\mathrm{MHz}$.

Doppler-broadened absorption and dispersion spectra of the Q(1) line in the first overtone band of ${\mathrm{H}}_2$ were recorded together with a comb-locked cavity-enhanced spectroscopy instrument. On the basis of the Hartmann-Tran profile, the absorption and dispersion spectra were fitted independently, resulting in two consistent sets of line profile parameters. The intensities obtained by the two methods reached an accuracy below 0.1%, and agree well with the theoretical results. This work not only provides a test of high-level quantum chemistry calculations of the simplest neutral molecule, but also demonstrates the potential for SI-traceable high-precision molecular density measurements based on laser spectroscopy.

We show that two-body losses induce a collective excitation in a harmonically trapped one-dimensional Bose gas, even in the absence of a quench in the trap or any other external perturbation. Focusing on the dissipatively fermionized regime, we perform an exact mode expansion of the rapidity distribution function and characterize the emergence of the collective motion. We find clear coherent oscillations in the widths of the gas both in position and rapidity space as well as in the phase-space quadrupole mode of the gas. We compare this motion to that of the well-known breathing mode in the absence of losses and find that they differ in the motion of the density profile. We also discuss the role of losses in the collective motion of the gas following various other protocols, such as the removal of losses after a finite hold time, and when the harmonic trap is also quenched.