Mercury and the superheavy element copernicium are investigated using equation-of-motion relativistic coupled-cluster (EOM-RCC) and configuration interaction plus many-body perturbation ($\mathrm{CI}+\mathrm{MBPT}$) theory methods. The key atomic properties, including ionization potentials, excitation energies, isotope field shift factors, and static electric dipole polarizabilities, are calculated for ground and low-lying excited states. The theoretical accuracy is assessed by comparing the calculated results for Hg with available experimental data, which serve as benchmarks. Furthermore, basis-set dependence in the EOM-RCC calculations and $d$-hole excitation in the $\mathrm{CI}+\mathrm{MBPT}$ method are systematically evaluated in order to reveal the source of uncertainties for the highly excited states. These results for Hg and Cn can serve as guidance for future experimental studies.

A gas-phase sample consisting of lithium iodide, $\mathrm{LiI}$, molecules and their dimer ${\left(\mathrm{LiI}\right)}_2$ are Coulomb exploded by an intense 25-fs laser pulse. In the case of $\mathrm{LiI}$, we focus on the double ionization that creates a pair of ${\mathrm{Li}}^{+}$ and ${\mathrm{I}}^{+}$ recoil ions. From the kinetic energy distribution of the ${\mathrm{Li}}^{+}$ ions, extracted using coincidence filtering, we determine the distribution of internuclear distances $P\left(R\right)$ via the ground-state potential curve of ${\mathrm{LiI}}^{2+}$ obtained from an ab initio calculation that accounts for non-Coulombic effects. We find that the center of $P\left(R\right)$ is close to the expected internuclear separation based on the three vibrational states of $\mathrm{LiI}$ populated, whereas the width of $P\left(R\right)$ exceeds the theoretical value by $\sim 52$%. We discuss whether fragmentation via excited ${\mathrm{LiI}}^{2+}$ potential curves affects the determination of $P\left(R\right)$. In the case of the dimer, ${\left(\mathrm{LiI}\right)}_2$, we observe kinetic energies and relative emission directions of ${\mathrm{Li}}^{+}, {\mathrm{I}}^{+}$, and ${\mathrm{I}}^{2+}$ recoil ions consistent with Coulomb explosion of the parallelogram-shaped dimer after removing up to six electrons by the laser pulse.

We propose a fully analytical method for describing high-order harmonic generation (HHG). This method is based on the strong-field approximation and electron-trajectory theory, but utilizes the perturbation expansion on the Keldysh parameter $\gamma$. This expansion allows us to clearly differentiate the nonadiabatic and adiabatic effects on HHG. We show that the nonadiabatic effect relating to high-order expansion depends on the laser wavelength and remarkably enhances the HHG yields for cases of short wavelengths, providing deeper insights into wavelength-dependent HHG yields which are important in producing attosecond pulses. Especially, our method provides the analytical and accurate descriptions of nonadiabatic exit velocity and position of the tunneling electron at the tunnel exit. These descriptions are meaningful for constructing a fully analytical and quantitative Coulomb-included HHG model, which is crucial in HHG-based attosecond measurement.

We study the effects of the intertube dipole-dipole interactions (DDIs) in recent experiments with arrays of nearly integrable one-dimensional (1D) dipolar Bose gases of ${}^{162}\mathrm{Dy}$ atoms. An earlier theoretical modeling ignored those interactions, which we include here via a modification of the 1D confining potentials. We investigate the effects of the intertube DDIs both during the state preparation and during the measurements of the rapidity distributions. We explore how the strength of the contact interactions and the magnetic-field angles modify the intertube DDI corrections. We find that those corrections slightly change both the properties of the equilibrium state and the rapidity measurements. Remarkably, however, the changes nearly cancel each other, resulting in measured rapidity distributions that are very close to those predicted in the absence of the intertube DDIs.

The nucleation and dynamics of vortices in the quasi-two-dimensional rotating dipolar Bose-Einstein condensate are explored by taking into account the Lee-Huang-Yang (LHY) correction to the mean-field (MF) theory. Assuming approximate cancellation of the MF interactions, we focus on the formation of a pure-LHY superfluid. The effect of rotational frequency $\mathrm{\Omega }$ is investigated numerically by determining the corresponding number of stable vortices in the superfluid, together with the respective energy per particle $E$ and chemical potential $\mu$. The LHY superfluid provides a deep minimum of $E$ and $\mu$, indicating that it is a remarkably robust state of quantum matter. By fixing the LHY interaction strength, an exact single-vortex critical frequency is found, along with the respective chemical potential. A notable feature, observed when creating the LHY superfluid with fewer than five vortices, which is understood as being due to the superfluid's nonlinearity and trapping aspect ratio, is the large frequency ranges admitting the production of two and four vortices, as compared to the small frequency ranges to obtain one and three vortices.

The propagation of intense, partially spatially coherent laser beams in a medium with instantaneous third-order susceptibility is studied analytically and numerically. For sufficiently high power relative to that required for nonlinear self-focusing, the propagation initially proceeds in two stages. In the first stage, spatial coherence builds up, and in the second stage, the number of speckles reduces. Once the degree of coherence is sufficiently high, whole-beam self-focusing occurs. The beam power is mostly confined within the initial spot radius. Two analytical approaches for describing the evolution of the beam are presented. The method of moments leads to an analytical solution for the rms spot radius that is in excellent agreement with simulations. This method does not require any knowledge of the field statistics beyond the initial conditions and provides no information about the evolution of the individual speckles. The other approach employs a self-similar solution for the second-order coherence function of the field and assumes that the fourth-order coherence function is factorizable and obeys complex circular Gaussian random statistics. The latter method also leads to an analytical expression for the spot radius, but its predictions for the qualitative evolution of the speckles disagree with wave-optics simulations.

We study the influence of many-body Coulomb interactions on higher-order harmonic generation (HHG) in bulk crystals. While these carrier-carrier interactions are traditionally believed to be less important for HHG in three-dimensional materials than in two-dimensional systems, quantitative characterization of their specific role in shaping the HHG spectrum is so far lacking. In this simulation-based study, we compare the HHG spectra with and without the inclusion of the carrier-carrier interactions at the Hartree-Fock level. Simulations performed under varying excitation conditions demonstrate that the Coulomb-related effects clearly show up in the high-harmonic spectra, significantly enhancing or suppressing different harmonic bands. We also demonstrate an algorithm to accelerate numerical calculation of the Coulomb interactions, which reduces the overall computational complexity of HHG simulations at the Hartree-Fock level.

The use of structured light as a quantum resource requires the ability to construct the density matrix of spin-orbit states from measurements. In this paper, we propose and experimentally demonstrate the tomography for a wide class of spin-orbit modes, including mixed modes. By combining polarimetry and image analysis of the transverse modes, we can obtain the density matrix of the corresponding quantum state with high fidelity. Informational completeness of the method is achieved through the analysis of the direct and astigmatic images of the spatial modes exiting each port of the polarimetric measurement. The required astigmatism is produced by a spherical lens suitably tilted with respect to the beam's propagation direction. This operation lifts the image degeneracy of modes carrying opposite orbital angular momenta and completes the information about the density matrix.

Cascaded quadratic nonlinearities provide a practical alternative to the intrinsically weak direct third-order nonlinearities in conventional optical systems, enabling effective emulation of strong cubic nonlinear processes. In this work, we theoretically demonstrate the generation of Schrödinger cat states via non-Gaussian quantum steering in cascaded spontaneous parametric downconversion, considering both partially degenerate and fully nondegenerate configurations. We show that the pump amplitude can be tuned to control the degree of non-Gaussianity and entanglement in the resulting three-photon states. By extending Reid's Einstein-Podolsky-Rosen criterion to higher-order quadrature moments, we reveal non-Gaussian steering that remains undetectable using standard first-order quadrature measurements. This contrast confirms that the cascaded process generates a genuinely non-Gaussian state whose essential quantum correlations are encoded in higher-order statistical moments. Furthermore, we demonstrate how these non-Gaussian steerable correlations enable the remote heralding of high-fidelity, large-amplitude two- and four-component Schrödinger cat states through conditional homodyne detection. Our work establishes a direct connection between higher-order quantum correlations and controllable non-Gaussian state engineering, offering additional possibilities for fundamental tests of quantum physics and optical quantum technologies.

Quantum routing of photons is an essential technique for building scalable quantum networks. In this work, we show that photons can be efficiently transferred between different ports via superatom quantum nodes, which are constructed by a couple of two-level atoms with direct couplings. We propose a multichannel scattering approach for studying photon transport in dual-waveguide systems. Quantum interference between collective quantum states is important for photon routing. We focus on superatom quantum nodes with two and three atoms, i.e., the atom dimer and trimer. By considering appropriate atomic spacings and direct couplings, port-selective high-efficiency photon routing can be achieved. Our work opens the way to superatom quantum routers in waveguide quantum networks.

We theoretically study the impact of magnetic sublevels on superradiance lattices (SLs) in room temperature ${}^{87}\mathrm{Rb}$ vapor. By incorporating the full Zeeman manifold into the master-equation framework, we demonstrate that the presence of magnetic sublevels significantly modifies the velocity-scanning tomography spectra of SLs. Our simulations reveal that two specific optical configurations exhibit clear lattice features while being robust against collision effects, making them favorable for experimental realization. Furthermore, we explore the influence of an external magnetic field, which lifts the degeneracy of Zeeman sublevels and enables multiple distinguishable SLs. These findings not only clarify the discrepancies between simplified SL models and experimental observations, but also pave the way for constructing spin-dependent SLs.

We investigate the problem of work extraction from a cavity-based quantum battery that is remotely charged via a transmission line composed of an array of coupled single-mode cavities. For uniform coupling along the line we show, via numerical analysis, that the ergotropy of the battery, evaluated at the point of maximum power transfer, decreases with the length of the charging line and vanishes beyond a critical size. By carefully engineering the initial state of the charger, nonzero ergotropy can still be harvested even beyond this critical length. We further examine scenarios in which the charging line is initialized in an entangled state, as well as configurations with nonuniform, parabolically varying, coupling strengths. In the latter case, we demonstrate that high ergotropy values can be restored, highlighting the potential for spatially engineered interactions to enhance quantum battery performance.

The theory of multiresonator quantum memory with atomic ensembles has been developed. Using the obtained analytical solutions, the basic physical properties of such memory are analyzed, and optimal conditions for its implementation are determined. Advantages of this quantum memory and its experimental implementation in integrated optical schemes are discussed.

Nonclassical states of bosonic modes, especially the large number states, are valuable resources for quantum information processing and quantum metrology. It is however intricate to generate a desired Fock state of bosonic systems by unitary protocols due to their uniform energy spectrum. We here propose a nonunitary protocol that is based on the resonant Jaynes-Cummings interaction of the bosonic mode with an ancillary two-level atom and sequential projective measurements on the atom. Using the generalized parity-measurement operator constructed by several rounds of free evolution with stepwise halved intervals and measurement, we can efficiently filter out the unwanted population and push the target resonator conditionally toward the desired Fock state. In the ideal situation, a Fock state $|n_t\approx 2000\rangle$ can be prepared with a fidelity over $98\%$ using only eight rounds of measurements. Under qubit dissipation and dephasing and cavity decay in the current circuit-QED platforms, a Fock state $|n_t\approx 100\rangle$ can be prepared with a fidelity of about $80\%$ by six measurements. It is found that the number of measurement rounds for preparing a large Fock state $|n_t\rangle$ scales roughly as ${log}_2\sqrt{n_t}$, which is similar to the number of ancillary qubits required in the state preparation via the quantum phase estimation algorithm and yet costs much less in gate operations. Our protocol can also be used to prepare a large Dicke state $|J\simeq 1000,0\rangle$ of a spin ensemble with a sufficiently high fidelity by less than six measurements. It is qualified by the quantum Fisher information approaching the Heisenberg scaling in sensing the rotation phase along the $x$ axis.

We propose a communication game in the sequential-measurement scenario involving a sender and two receivers with restricted communication among the latter parties. In the framework of the prepare-transform-measure scenario, we find a prominent quantum advantage in the receiver's decoding of the message originally encoded by the sender. We show that an optimal trade-off between the success probabilities of the two receivers enables self-testing of the sender's state preparation, the first receiver's instruments, and the measurement device of the second receiver in a semi-device-independent way. Our protocol enables a more robust certification of the unsharp measurement parameter of the first receiver compared to an earlier protocol. We further generalize our game to higher-dimensional systems, revealing greater quantum advantage with an increase in dimensions.

A crucial component of photonic quantum information processing platforms is the ability to modulate, route, convert, and switch quantum states of light noiselessly with low insertion loss. For instance, a high-speed, low-loss optical switch is crucial for scaling quantum photonic systems that rely on measurement-based feed-forward approaches. Such a device will also ideally be capable of operating on photon-number states, which can act as non-Gaussian resources. Here, we demonstrate ultrafast all-optical switching of heralded photon-number states, of up to six photons, using the optical Kerr effect in a single-mode fiber. A local birefringence is created by a high-intensity pump pulse at a center wavelength of 1030 nm which overlaps temporally with the 1550 nm photons in the fiber. A switching efficiency of $>99\%$ is reached with a resolution of 2.3 ps, an insertion loss of $2.27\pm 0.08\mathrm{dB}$, and a signal-to-noise ratio of $32000$.

Using the configuration-interaction plus coupled-cluster approach, we calculate the electric-field gradients $q$ for the low-lying states of alkaline-earth atoms, including magnesium (Mg), strontium (Sr), and barium (Ba). These low-lying states specifically include the $3s3p{}^{3}P_{1,2}$ states of Mg; the $5s4d{}^{1}D_2$ and $5s5p{}^{3}P_{1,2}$ states of Sr; as well as the $6s5d{}^{3}D_{1,2,3}, 6s5d{}^{1}D_2$, and $6s6p{}^{1}P_1$ states of Ba. By combining the measured electric quadrupole hyperfine-structure constants of these states, we accurately determine the nuclear quadrupole moments of ${}^{25}\mathrm{Mg}, {}^{87}\mathrm{Sr}$, and ${}^{135,137}\mathrm{Ba}$. These results are compared with the available data. The comparison shows that our nuclear quadrupole moment of ${}^{25}\mathrm{Mg}$ is in perfect agreement with the result from the mesonic x-ray experiment. However, there are approximately 10% and 4% differences between our results and the currently adopted values [Pyykkö, Mol. Phys. 116, 1328 (2018)] for the nuclear quadrupole moments of ${}^{87}\mathrm{Sr}$ and ${}^{135,137}\mathrm{Ba}$, respectively. Moreover, we also calculate the magnetic dipole hyperfine-structure constants of these states, and the calculated results exhibit good agreement with the measured data.

We present a magnetic trapping scheme for cold ${}^{87}\mathrm{Rb}$ atoms based on light-induced fictitious magnetic fields generated by the evanescent field of an optical nanofiber (ONF) integrated with optical tweezers. We calculate and compare the trapping potentials for both Gaussian and Laguerre-Gaussian modes of the tweezer beam, combined with a quasilinearly polarized ONF-guided field. Based on the optical powers in the tweezer and ONF modes, we analyze the trap depths and the positions of the potential minima from the nanofiber surface. We show that, by varying the optical powers in the two fields, the trap position can be tuned over several hundred nanometers while simultaneously influencing the trap depth and trap frequencies. Such control over the atom-surface position is essential for studying distance-dependent effects on atoms trapped near a dielectric surface and optimizing atom-photon interfaces for quantum technology applications.