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<jats:p>A random quantum circuit is a minimally structured model to study entanglement dynamics of many-body quantum systems. We consider a one-dimensional quantum circuit with noisy Haar-random unitary gates using density matrix operator and tensor contraction methods. It is shown that the entanglement evolution of the random quantum circuits is properly characterized by the logarithmic entanglement negativity. By performing exact numerical calculations, we find that, as the physical error rate is decreased below a critical value <jats:italic>p</jats:italic> <jats:sub>c</jats:sub> ≈ 0.056, the logarithmic entanglement negativity changes from the area law to the volume law, giving rise to an entanglement transition. The critical exponent of the correlation length can be determined from the finite-size scaling analysis, revealing the universal dynamic property of the noisy intermediate-scale quantum devices.</jats:p>

<jats:p>Catastrophic forgetting describes the fact that machine learning models will likely forget the knowledge of previously learned tasks after the learning process of a new one. It is a vital problem in the continual learning scenario and recently has attracted tremendous concern across different communities. We explore the catastrophic forgetting phenomena in the context of quantum machine learning. It is found that, similar to those classical learning models based on neural networks, quantum learning systems likewise suffer from such forgetting problem in classification tasks emerging from various application scenes. We show that based on the local geometrical information in the loss function landscape of the trained model, a uniform strategy can be adapted to overcome the forgetting problem in the incremental learning setting. Our results uncover the catastrophic forgetting phenomena in quantum machine learning and offer a practical method to overcome this problem, which opens a new avenue for exploring potential quantum advantages towards continual learning.</jats:p>

<jats:p>We design generative neural networks that generate Monte Carlo configurations with complete absence of autocorrelation from which only short Markov chains are needed before making measurements for physical observables, irrespective of the system locating at the classical critical point, fermionic Mott insulator, Dirac semimetal, or quantum critical point. We further propose a network-initialized Monte Carlo scheme based on such neural networks, which provides independent samplings and can accelerate the Monte Carlo simulations by significantly reducing the thermalization process. We demonstrate the performance of our approach on the two-dimensional Ising and fermion Hubbard models, expect that it can systematically speed up the Monte Carlo simulations especially for the very challenging many-electron problems.</jats:p>

<jats:p>We study the hybrid mesons with the exotic quantum number <jats:italic>I</jats:italic> <jats:sup>G</jats:sup> <jats:italic>J</jats:italic> <jats:sup>PC</jats:sup> = 0<jats:sup>+</jats:sup>1<jats:sup>−+</jats:sup> and investigate their decays into the <jats:italic>η η</jats:italic>′, <jats:italic>a</jats:italic> <jats:sub>1</jats:sub>(1260) <jats:italic>π</jats:italic>, <jats:italic>f</jats:italic> <jats:sub>1</jats:sub>(1285) <jats:italic>η</jats:italic>, <jats:italic>f</jats:italic> <jats:sub>1</jats:sub>(1420) <jats:italic>η</jats:italic>, <jats:inline-formula> <jats:tex-math><?CDATA ${K}^{* }(892)\bar{K}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>*</mml:mo> </mml:msup> <mml:mo stretchy="false">(</mml:mo> <mml:mn>892</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mover accent="true"> <mml:mi>K</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_39_5_051201_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:inline-formula> <jats:tex-math><?CDATA ${K}_{1}(1270)\bar{K}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>K</mml:mi> <mml:mn>1</mml:mn> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1270</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mover accent="true"> <mml:mi>K</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_39_5_051201_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, and <jats:inline-formula> <jats:tex-math><?CDATA ${K}_{1}(1400)\bar{K}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>K</mml:mi> <mml:mn>1</mml:mn> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1400</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mover accent="true"> <mml:mi>K</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_39_5_051201_ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> channels. It is found that the QCD axial anomaly enhances the decay width of the <jats:italic>η η</jats:italic>′ channel although this mode is strongly suppressed by the small p-wave phase space. Our results support the interpretation of the <jats:italic>η</jats:italic> <jats:sub>1</jats:sub>(1855) recently observed by BESIII as the <jats:inline-formula> <jats:tex-math><?CDATA $\bar{s}sg$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mover accent="true"> <mml:mi>s</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>s</mml:mi> <mml:mi>g</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_39_5_051201_ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> hybrid meson of <jats:italic>I</jats:italic> <jats:sup>G</jats:sup> <jats:italic>J</jats:italic> <jats:sup>PC</jats:sup> = 0<jats:sup>+</jats:sup>1<jats:sup>−+</jats:sup>. The QCD axial anomaly ensures the <jats:italic>η η</jats:italic>′ decay mode to be a characteristic signal of the hybrid nature of the <jats:italic>η</jats:italic> <jats:sub>1</jats:sub>(1855).</jats:p>

<jats:p>We theoretically investigate terahertz emission from solid materials pumped by intense two-color femtosecond laser field in the presence of decoherence effects. Quantum-mechanical simulations are based on the length gauge semiconductor Bloch equations describing the optical excitation and decoherence with phenomenological dephasing and depopulation times. Contributions of interband and intraband mechanisms are identified in time domain, and the latter has dominated THz generation in solid-state systems. It is found that dephasing is crucial for enhancing asymmetric intraband current and deduced that solid-state materials with short dephasing time and long depopulation time would be optimal selection for strong-field terahertz generation experiments.</jats:p>

<jats:p>The hybridization of fullerene and nanotube structures in newly isolated C<jats:sub>90</jats:sub> with the <jats:italic>D</jats:italic> <jats:sub>5<jats:italic>h</jats:italic> </jats:sub> symmetric group (<jats:italic>D</jats:italic> <jats:sub>5<jats:italic>h</jats:italic> </jats:sub>(1)-C<jats:sub>90</jats:sub>) provides an ideal model as a mediating allotrope of nanocarbon from zero-dimensional (0D) fullerene to one-dimensional nanotube. Raman and infrared spectroscopy combined with classical molecular dynamics simulation were used to investigate the structural evolution of <jats:italic>D</jats:italic> <jats:sub>5<jats:italic>h</jats:italic> </jats:sub>(1)-C<jats:sub>90</jats:sub> at ambient and high pressure up to 35.1 GPa. Interestingly, the high-pressure transformations of <jats:italic>D</jats:italic> <jats:sub>5<jats:italic>h</jats:italic> </jats:sub>(1)-C<jats:sub>90</jats:sub> exhibit the features of both fullerene and nanotube. At around 2.5 GPa, the <jats:italic>D</jats:italic> <jats:sub>5<jats:italic>h</jats:italic> </jats:sub>(1)-C<jats:sub>90</jats:sub> molecule in the crystal undergoes an orientational transition to a restricted rotation. At 6.6 GPa, the tubular hexagonal part occurs and transforms into a dumbbell-like structure at higher pressure. The material starts to amorphize above 13.9 GPa, and the transition is reversible until the pressure exceeds 25 GPa. The amorphization is probably correlated with both the intermolecular bonding and the morphology change. Our results enrich our understanding of structural changes in nanocarbon from 0D to 1D.</jats:p>

<jats:p>Neon (Ne) can reveal the evolution of planets, and nitrogen (N) is the most abundant element in the Earth’s atmosphere. Considering the inertness of neon, whether nitrogen and neon can react has aroused great interest in condensed matter physics and space science. Here, we identify three new Ne–N compounds (i.e., NeN<jats:sub>6</jats:sub>, NeN<jats:sub>10</jats:sub>, and NeN<jats:sub>22</jats:sub>) under pressure by first-principles calculations. We find that inserting Ne into N<jats:sub>2</jats:sub> substantially decreases the polymeric pressure of the nitrogen and promotes the formation of abundant polynitrogen structures. Especially, NeN<jats:sub>22</jats:sub> acquires a duplex host-guest structure, in which guest atoms (Ne and N<jats:sub>2</jats:sub> dimers) are trapped inside the crystalline host N<jats:sub>20</jats:sub> cages. Importantly, both NeN<jats:sub>10</jats:sub> and NeN<jats:sub>22</jats:sub> not only are dynamically and mechanically stable but also have a high thermal stability up to 500 K under ambient pressure. Moreover, ultra-high energy densities are obtained in NeN<jats:sub>10</jats:sub> (11.1 kJ/g), NeN<jats:sub>22</jats:sub> (11.5 kJ/g), tetragonal t-N<jats:sub>22</jats:sub> (11.6 kJ/g), and t-N<jats:sub>20</jats:sub> (12.0 kJ/g) produced from NeN<jats:sub>22</jats:sub>, which are more than twice the value of trinitrotoluene (TNT). Meanwhile, their explosive performance is superior to that of TNT. Therefore, NeN<jats:sub>10</jats:sub>, NeN<jats:sub>22</jats:sub>, t-N<jats:sub>22</jats:sub>, and t-N<jats:sub>20</jats:sub> are promising green high-energy-density materials. This work promotes the study of neon-nitrogen compounds with superior properties and potential applications.</jats:p>

<jats:p>Fractonic superfluids are exotic states of matter with spontaneously broken higher-rank <jats:italic>U</jats:italic>(1) symmetry. The broken symmetry is associated with conserved quantities, including not only particle number (i.e., charge) but also higher moments, such as dipoles, quadrupoles, and angular moments. Owing to the presence of such conserved quantities, the mobility of particles is restricted either completely or partially. Here, we systematically study the hydrodynamical properties of fractonic superfluids, especially focusing on the fractonic superfluids with conserved angular moments. The constituent bosons are called “lineons” with <jats:italic>d</jats:italic> components in <jats:italic>d</jats:italic>-dimensional space. From the Euler–Lagrange equation, we derive the continuity equation and Navier–Stokes-like equations, in which the angular moment conservation introduces extra terms. Further, we discuss the current configurations related to the defects. Like the conventional superfluid, we study the critical values of velocity fields and density currents, which gives rise to a Landau-like criterion. Finally, several future directions are discussed.</jats:p>

<jats:p>We report a study of fermiology, electrical anisotropy, and Fermi liquid properties in the layered ternary boride MoAlB, which could be peeled into two-dimensional (2D) metal borides (MBenes). By studying the quantum oscillations in comprehensive methods of magnetization, magnetothermoelectric power, and torque with the first-principle calculations, we reveal three types of bands in this system, including two 2D-like electronic bands and one complex three-dimensional-like hole band. Meanwhile, a large out-of-plane electrical anisotropy (<jats:italic>ρ<jats:sub>bb</jats:sub> </jats:italic>/<jats:italic>ρ<jats:sub>aa</jats:sub> </jats:italic> ∼ 1100 and <jats:italic>ρ<jats:sub>bb</jats:sub> </jats:italic>/<jats:italic>ρ<jats:sub>cc</jats:sub> </jats:italic> ∼ 500, at 2 K) was observed, which is similar to those of the typical anisotropic semimetals but lower than those of some semiconductors (up to 10<jats:sup>5</jats:sup>). After calculating the Kadowaki–Woods ratio (KWR = <jats:italic>A</jats:italic>/<jats:italic>γ</jats:italic> <jats:sup>2</jats:sup>), we observed that the ratio of the in-plane <jats:italic>A</jats:italic> <jats:sub> <jats:italic>a</jats:italic>,<jats:italic>c</jats:italic> </jats:sub>/<jats:italic>γ</jats:italic> <jats:sup>2</jats:sup> is closer to the universal trend, whereas the out-of-plane <jats:italic>A</jats:italic> <jats:sub> <jats:italic>b</jats:italic> </jats:sub>/<jats:italic>γ</jats:italic> <jats:sup>2</jats:sup> severely deviates from the universality. This demonstrates a 2D Fermi liquid behavior. In addition, MoAlB cannot be unified using the modified KWR formula like other layered systems (Sr<jats:sub>2</jats:sub>RuO<jats:sub>4</jats:sub> and MoOCl<jats:sub>2</jats:sub>). This unique feature necessitates further exploration of the Fermi liquid property of this layered molybdenum compound.</jats:p>

<jats:p>Scanning tunneling microscopy is a powerful tool to build artificial atomic structures that do not exist in nature but possess exotic properties. In this study, we constructed Lieb lattices with different lattice constants by real atoms, i.e., Fe atoms on Ag(111), and probed their electronic properties. We obtain a surprising long-range effective electron wavefunction overlap between Fe adatoms as it exhibits a <jats:inline-formula> <jats:tex-math> <?CDATA $\displaystyle \frac{1}{{r}^{2}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mstyle displaystyle="true"> <mml:mfrac> <mml:mn>1</mml:mn> <mml:mrow> <mml:msup> <mml:mi>r</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:mfrac> </mml:mstyle> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_39_5_057301_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> dependence with the interatomic distance <jats:italic>r</jats:italic> instead of the theoretically predicted exponential one. Combining control experiments, tight-binding modeling, and Green’s function calculations, we attribute the observed long-range overlap to being enabled by the surface state. Our findings enrich the understanding of the electron wavefunction overlap and provide a convenient platform to design and explore artificial structures and future devices with real atoms.</jats:p>