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<jats:p>Modern and anticipated facilities will deliver data that promises to reveal the innermost workings of quantum chromodynamics (QCD). In order to fulfill that promise, phenomenology and theory must reach a new level, limiting and overcoming model-dependence, so that clean lines can be drawn to connect the data with QCD itself. Progress in that direction, made using continuum methods for the hadron bound-state problem, is sketched herein.</jats:p>

<jats:p>The opacities of the lithium hydride molecule are calculated for temperatures of 300 K, 1000 K, 1500 K, and 2000 K, at a pressure of 10 atm, in which the contributions from the five low-lying electronic states are considered. The <jats:italic>ab initio</jats:italic> multi-reference single and double excitation configuration interaction (MRDCI) method is applied to compute the potential energy curves (PECs) of the <jats:sup>7</jats:sup>LiH, including four <jats:sup>1</jats:sup> <jats:italic>Σ</jats:italic> <jats:sup>+</jats:sup> states and one <jats:sup>1</jats:sup> <jats:italic>Π</jats:italic> state, as well as the corresponding transition dipole moments between these states. The ro-vibrational energy levels are calculated based on the PECs obtained, together with the spectroscopic constants. In addition, the partition functions are also computed, and are provided at temperatures ranging from 10 K to 2000 K for <jats:sup>7</jats:sup>LiH, <jats:sup>7</jats:sup>LiD, <jats:sup>6</jats:sup>LiH, and <jats:sup>6</jats:sup>LiD.</jats:p>

<jats:p>Ultralong-range Cs<jats:sub>2</jats:sub> Rydberg-ground molecules (<jats:italic>nD</jats:italic> <jats:sub>5/2</jats:sub> + 6<jats:italic>S</jats:italic> <jats:sub>1/2</jats:sub> <jats:italic>F</jats:italic>) (33 ≤ <jats:italic>n</jats:italic> ≤ 39, <jats:italic>F</jats:italic> = 3 or 4) are investigated by a two-photon photo-association spectroscopy of an ultracold Cs gas. Two vibrational ground molecular spectra of triplet <jats:sup>3</jats:sup> <jats:italic>Σ</jats:italic> and hyperfine mixed singlet-triplet <jats:sup>1,3</jats:sup> <jats:italic>Σ</jats:italic> molecular states and their corresponding binding energies are attained. The experimental observations are simulated by an effective Hamiltonian including low energy electron scattering pseudopotentials, the spin-orbit interaction of the Rydberg atom, and the hyperfine interaction of the ground-state atom. The zero-energy singlet and triplet s-wave scattering lengths are extracted by comparing the experimental observations and calculations. Dependences of the measured binding energies on the effective principal quantum number, <jats:italic>n</jats:italic> <jats:sub>eff</jats:sub> = <jats:italic>n</jats:italic> − <jats:italic>δ<jats:sub>D</jats:sub> </jats:italic> (<jats:italic>δ<jats:sub>D</jats:sub> </jats:italic> is the quantum defect of Rydberg <jats:italic>D</jats:italic> state), yield the scaling of <jats:inline-formula> <jats:tex-math> <?CDATA ${n}_{{\rm{eff}}}^{-5.60\pm 0.16}{(}^{3}{\rm{}}\varSigma,F=3)$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>n</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">eff</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>5.60</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.16</mml:mn> </mml:mrow> </mml:msubsup> <mml:msup> <mml:mo stretchy="false">(</mml:mo> <mml:mn>3</mml:mn> </mml:msup> <mml:mi mathvariant="normal">​</mml:mi> <mml:mi>Σ</mml:mi> <mml:mo>,</mml:mo> <mml:mi>F</mml:mi> <mml:mo>=</mml:mo> <mml:mn>3</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_37_12_123201_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:inline-formula> <jats:tex-math> <?CDATA ${n}_{{\rm{eff}}}^{-5.62\pm 0.16}{(}^{3}{\rm{}}\varSigma,F=4)$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>n</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">eff</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>5.62</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.16</mml:mn> </mml:mrow> </mml:msubsup> <mml:msup> <mml:mo stretchy="false">(</mml:mo> <mml:mn>3</mml:mn> </mml:msup> <mml:mi mathvariant="normal">​</mml:mi> <mml:mi>Σ</mml:mi> <mml:mo>,</mml:mo> <mml:mi>F</mml:mi> <mml:mo>=</mml:mo> <mml:mn>4</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_37_12_123201_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> for deep triplet potential and <jats:inline-formula> <jats:tex-math> <?CDATA ${n}_{{\rm{eff}}}^{-5.65\pm 0.38}{(}^{1,3}{\rm{}}\varSigma,F=3)$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>n</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">eff</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>5.65</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.38</mml:mn> </mml:mrow> </mml:msubsup> <mml:msup> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>,</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mi mathvariant="normal">​</mml:mi> <mml:mi>Σ</mml:mi> <mml:mo>,</mml:mo> <mml:mi>F</mml:mi> <mml:mo>=</mml:mo> <mml:mn>3</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_37_12_123201_ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:inline-formula> <jats:tex-math> <?CDATA ${n}_{{\rm{eff}}}^{-6.19\pm 0.14}{(}^{1,3}{\rm{}}\varSigma,F=4)$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>n</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">eff</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>6.19</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.14</mml:mn> </mml:mrow> </mml:msubsup> <mml:msup> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>,</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mi mathvariant="normal">​</mml:mi> <mml:mi>Σ</mml:mi> <mml:mo>,</mml:mo> <mml:mi>F</mml:mi> <mml:mo>=</mml:mo> <mml:mn>4</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_37_12_123201_ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> for shallow mixed singlet-triplet potential well. The simulations of low-energy Rydberg electron scattering show agreement well with the experimental measurements.</jats:p>

<jats:p>Based on a parabolic coordinate system, we theoretically design and experimentally generate hybridly polarized vector optical fields with parabolic symmetry of the first and second kinds, which can further enrich the family of vector optical fields. The wavefront of this new-kind vector optical field contains circular, elliptic and linear polarizations, and the polarizations can keep the same or change along the parabolic curves. Then we present the realization of tunable focal shift with the hybridly polarized vector optical field, and show a specific law of the focal shift of the focused hybridly polarized vector optical field with the parabolic symmetry. We hope these results can provide a new way to flexibly modulate focal fields, which can be applied in realms such as optical machining, optical trapping and information transmission.</jats:p>

<jats:p>We study the evolution of spectral intensity and degree of coherence of a new class of partially coherent beams, Hermite non-uniformly correlated array beams, in free space and in turbulence, based on the extended Huygens–Fresnel integral. Such beams possess controllable rectangular grid distributions due to multi-self-focusing propagation property. Furthermore, it is demonstrated that adjusting the initial beam parameters, mode order, shift parameters, array parameters and correlation width plays a role in resisting intensity and degree of coherence degradation effects of the turbulence.</jats:p>

<jats:p>Extreme ultraviolet (XUV) frequency comb is a powerful tool in precision measurement. It also brings many new opportunities to the field of strong field physics since high harmonic generation related phenomena can be studied with high repetition rate. We demonstrate the generation of an XUV frequency comb with the aid of intra-cavity high harmonic generation process. The setup is driven by a high power infrared frequency comb, and an average power of 4.5 kW is reached in the femtosecond enhancement cavity. With Xe gas as the working media, harmonics up to the 19th order are observed. Power measurement indicates that as much as 115.9 <jats:italic>μ</jats:italic>W (1.3 mW) are generated at ∼94 nm (∼148 nm). The shortest wavelength we can reach is ∼55 nm. The coherence of the generated light is tested with an optical-heterodyne-based measurement of the third harmonic. The resulted line width is ∼3 Hz. In addition, with this system, we also observe a strong suppression of below threshold harmonics from O<jats:sub>2</jats:sub> compared to that from Xe. These results suggest that the current system is ready for precision spectroscopic measurements with few-electron atomic and molecular systems in XUV region as well as the study of strong field physics with an unprecedented 100MHz repetition rate.</jats:p>

<jats:p>The accurate and rapid prediction of materials’ physical properties, such as thermal transport and mechanical properties, are of particular importance for potential applications of featuring novel materials. We demonstrate, using graphene as an example, how machine learning potential, combined with the Boltzmann transport equation and molecular dynamics simulations, can simultaneously provide an accurate prediction of multiple-target physical properties, with an accuracy comparable to that of density functional theory calculation and/or experimental measurements. Benchmarked quantities include the Grüneisen parameter, the thermal expansion coefficient, Young’s modulus, Poisson’s ratio, and thermal conductivity. Moreover, the transferability of commonly used empirical potential in predicting multiple-target physical properties is also examined. Our study suggests that atomic simulation, in conjunction with machine learning potential, represents a promising method of exploring the various physical properties of novel materials.</jats:p>

<jats:p>Two-dimensional (2D) materials and their corresponding van der Waals (vdW) heterostructures are considered as promising candidates for highly efficient solar cell applications. A series of 2D HfX<jats:sub>2</jats:sub> (X = Cl, Br, I) monolayers are proposed, via first-principle calculations. The vibrational phonon spectra and molecular dynamics simulation results indicate that HfX<jats:sub>2</jats:sub> monolayers possess dynamical and thermodynamical stability. Moreover, their electronic structure shows that their Heyd–Scuseria–Ernzerhof(HSE06)-based band values (1.033–1.475 eV) are suitable as donor systems for excitonic solar cells (XSCs). The material’s significant visible-light absorbing capability (∼10<jats:sup>5</jats:sup> cm<jats:sup>−1</jats:sup>) and superior power conversion efficiency (∼20%) are demonstrated by establishing a reasonable type II vdW heterostructure. This suggests the significant potential of HfX<jats:sub>2</jats:sub> monolayers as a candidate material for XSCs.</jats:p>

<jats:p>The exotic electronic band structures of Ruby and Star lattices, characterized by Dirac cone and nontrivial topology, offer a unique platform for the study of two-dimensional (2D) Dirac materials. In general, an ideal isotropic Dirac cone is protected by time reversal symmetry and inversion, so that its robustness against lattice distortion is not only of fundamental interest but also crucial to practical applications. Here we systematically investigate the robustness of Dirac cone in a Ruby lattice against four typical lattice distortions that break the inversion and/or mirror symmetry in the transition from Ruby to Star. Using a tight-binding approach, we show that the isotropic Dirac cones and their related topological features remain intact in the rotationally distorted lattices that preserve the inversion symmetry (<jats:italic>i</jats:italic>-Ruby lattice) or the in-plane mirror symmetry (<jats:italic>m</jats:italic>-Ruby lattice). On the other hand, the Dirac cones are gapped in the <jats:italic>a</jats:italic>- and <jats:italic>b</jats:italic>-Ruby lattices that break both these lattice symmetries or inversion. Furthermore, a rotational unitary matrix is identified to transform the original into the distorted lattice. The symmetry-protected Dirac cones were also verified in photonic crystal systems. The robust Dirac cones revealed in the non-mirror symmetric <jats:italic>i</jats:italic>-Ruby and non-centrosymmetric <jats:italic>m</jats:italic>-Ruby lattices provide a general guidance for the design of 2D Dirac materials.</jats:p>