Quantum key distribution (QKD) generates information-theoretical secret keys between two parties based on the physical laws of quantum mechanics. Following the advancement in quantum communication networks, it becomes feasible and economical to combine QKD with classical optical communication through the same fiber using dense wavelength division multiplexing (DWDM) technology. This study proposes a detailed scheme of TF-QKD protocol with DWDM technology and analyzes its performance, considering the influence of quantum channel number and adjacent quantum crosstalk on the secret key rates. The simulation results show that the scheme further increases the secret key rate of TF-QKD and its variants. Therefore, this scheme provides a method for improving the secret key rate for practical quantum networks.

Quantum steering in a global state allows an observer to remotely steer a subsystem into different ensembles by performing different local measurements on the other part. We show that, in general, this property cannot be perfectly cloned by any joint operation between a steered subsystem and a third system. Perfect cloning is viable if and only if the initial state is of zero discord. We also investigate the process of cloning the steered qubit of a Bell state using a universal cloning machine. Einstein–Podolsky–Rosen (EPR) steering, which is a type of quantum correlation existing in the states without a local-hidden-state model, is observed in the two copy subsystems. This contradicts the conclusion of no-cloning of quantum steering (EPR steering) [C. Y. Chiu et al., npj Quantum Inf. 2, 16020 (2016)] based on a mutual information criterion for EPR steering.

As a fundamental tool in the quantum information field, quantum state tomography can be used to reconstruct any unknown state. Generally, it needs a tomographically complete set of measurements, such that all measurements are fully characterized. Here, we propose a semi-measurement-device-independent quantum state tomography protocol, which only needs one characterized measurement and a trusted ancillary system. Furthermore, we perform corresponding experiments using linear optics. Our results show that the average state fidelity is as high as 0.973, verifying the effectiveness of the scheme.

By quenching the interatomic interactions, we investigate the nonequilibrium dynamics of two-dimensional Bose–Einstein condensates in boxlike traps with power-law potential boundaries. We show that ring dark solitons can be excited during the quench dynamics for both concave and convex potentials. The quench's modulation strength and the steepness of the boundary are two major factors influencing the system's evolution. In terms of the number of ring dark solitons excited in the condensate, five dynamic regimes have been identified. The condensate undergoes damped radius oscillation in the absence of ring dark soliton excitations. When it comes to the appearance of ring dark solitons, their decay produces interesting structures. The excitation patterns for the concave potential show a nested structure of vortex-antivortex pairs. The dynamic excitation patterns for the convex potential, on the other hand, show richer structures with multiple transport behaviors.

Cryo-electron microscopy (cryo-EM) provides a powerful tool to resolve the structure of biological macromolecules in natural state. One advantage of cryo-EM technology is that different conformation states of a protein complex structure can be simultaneously built, and the distribution of different states can be measured. This provides a tool to push cryo-EM technology beyond just to resolve protein structures, but to obtain the thermodynamic properties of protein machines. Here, we used a deep manifold learning framework to get the conformational landscape of KaiC proteins, and further obtained the thermodynamic properties of this central oscillator component in the circadian clock by means of statistical physics.

The quantum chromodynamics (QCD) coupling $\alpha_{\rm s}$ is the most important parameter for achieving precise QCD predictions. By using the well measured effective coupling $\alpha^{g_1}_{\rm s}(Q)$ defined from the Bjorken sum rules as a basis, we suggest a novel self-consistency way to fix the $\alpha_{\rm s}$ at all scales: The QCD light-front holographic model is adopted for its infrared behavior, and the fixed-order pQCD prediction under the principle of maximum conformality (PMC) is used for its high-energy behavior. Using the PMC scheme-and-scale independent perturbative series, and by transforming it into the one under the physical V scheme, we observe that a precise $\alpha_{\rm s}$ running behavior in both the perturbative and nonperturbative domains with a smooth transition from small to large scales can be achieved.

Effective Hamiltonians in periodically driven systems have received widespread attention for realization of novel quantum phases, non-equilibrium phase transition, and Majorana mode. Recently, the study of effective Hamiltonian using various methods has gained great interest. We consider a vector differential equation of motion to derive the effective Hamiltonian for any periodically driven two-level system, and the dynamics of the spin vector are an evolution under the Bloch sphere. Here, we investigate the properties of this equation and show that a sudden change of the effective Hamiltonian is expected. Furthermore, we present several exact relations, whose expressions are independent of the different starting points. Moreover, we deduce the effective Hamiltonian from the high-frequency limit, which approximately equals the results in previous studies. Our results show that the vector differential equation of motion is not affected by a convergence problem, and thus, can be used to numerically investigate the effective models in any periodic modulating system. Finally, we anticipate that the proposed method can be applied to experimental platforms that require time-periodic modulation, such as ultracold atoms and optical lattices.

We conducted measurement and calculation to resolve the long-standing large discrepancy in the metastable state lifetime for the $^{88}$Sr atom between theoretical and experimental results. The present lifetime $\tau = 830_{-240}^{+600}$ s, measured using the magneto-optical trap as a photon amplifier to detect the weak decay events, is approximately 60% larger than the previous experimental value $\tau = 520_{-140}^{+310}$ s. By considering the electron correlation effects in the framework of the multiconfiguration Dirac–Hartree–Fock theory, we obtained a theoretical lifetime of 1079(54) s, which lies in the range of measurements with error bars. Furthermore, we considered the higher-order electron correlation and Breit interaction to control the uncertainty of the theoretical calculation. The significant improvement in the agreement between calculations and measurements is attributed to the updated blackbody radiation-induced decay rate.

Plasma technology has widespread applications in many fields, whereas the methods for manipulating plasma transport are limited to magnetic control. In this study, we used a simplified diffusion-migration approach to describe plasma transport. The feasibility of the transformation theory for plasma transport was demonstrated. As potential applications, we designed three model devices capable of cloaking, concentrating, and rotating plasmas without disturbing the density profile of plasmas in the background. This research may help advance plasma technology in practical fields, such as medicine and chemistry.

Helium is the second most abundant element in the universe, and together with silica, they are important components of giant planets. Exploring the reactivity and state of helium and silica under high pressure is crucial for understanding of the evolution and internal structure of giant planets. Here, using first-principles calculations and crystal structure predictions, we identify four stable phases of a helium-silica compound with seven/eight-coordinated silicon atoms at pressure of 600–4000 GPa, corresponding to the interior condition of the outer planets in the solar system. The density of HeSiO$_{2}$ agrees with current structure models of the planets. This helium-silica compound exhibits a superionic-like helium diffusive state under the high-pressure and high-temperature conditions along the isentropes of Saturn, a metallic fluid state in Jupiter, and a solid state in the deep interiors of Uranus and Neptune. These results show that helium may affect the erosion of the rocky core in giant planets and may help to form a diluted core region, which not only highlight the reactivity of helium under high pressure but also provide evidence helpful for building more sophisticated interior models of giant planets.

NdNiO$_3$ is a typical correlated material with temperature-driven metal–insulator transition. Resolving the local electronic phase is crucial in understanding the driving mechanism behind the phase transition. Here we present a nano-infrared study of the metal–insulator transition in NdNiO$_3$ films by a cryogenic scanning near-field optical microscope. The NdNiO$_3$ films undergo a continuous transition without phase coexistence. The nano-infrared signal shows significant temperature dependence and a hysteresis loop. Stripe-like modulation of the optical conductivity is formed in the films and can be attributed to the epitaxial strain. These results provide valuable evidence to understand the coupled electronic and structural transformations in NdNiO$_3$ films at the nano-scale.

We investigate the topological phase transition driven by non-local electronic correlations in a realistic quantum anomalous Hall model consisting of $d_{xy}$–$d_{x^{2}-y^{2}}$ orbitals. Three topologically distinct phases defined in the non-interacting limit evolve to different charge density wave phases under correlations. Two conspicuous conclusions were obtained: The topological phase transition does not involve gap-closing and the dynamical fluctuations significantly suppress the charge order favored by the next nearest neighbor interaction. Our study sheds light on the stability of topological phase under electronic correlations, and we demonstrate a positive role played by dynamical fluctuations that is distinct to all previous studies on correlated topological states.

Tuning the bandgap in layered transition metal dichalcogenides (TMDCs) is crucial for their versatile applications in many fields. The ternary formation is a viable method to tune the bandgap as well as other intrinsic properties of TMDCs, because the multi-elemental characteristics provide additional tunability at the atomic level and advantageously alter the physical properties of TMDCs. Herein, ternary Ti$_{x}$Zr$_{1-x}$Se$_{2}$ single crystals were synthesized using the chemical-vapor-transport method. The changes in electronic structures of ZrSe$_{2}$ induced by Ti substitution were revealed using angle-resolved photoemission spectroscopy. Our data show that at a low level of Ti substitution, the bandgap of Ti$_{x}$Zr$_{1-x}$Se$_{2}$ decreases monotonically, and the electronic system undergoes a transition from a semiconducting to a metallic state without a significant variation of dispersions of valence bands. Meanwhile, the size of spin-orbit splitting dominated by Se $4p$ orbitals decreases with the increase of Ti doping. Our work shows a convenient way to alter the bandgap and spin-orbit coupling in TMDCs at the low level of substitution of transition metals.

Superlattice potentials are theoretically predicted to modify the single-particle electronic structures. The resulting Coulomb-interaction-dominated low-energy physics would generate highly novel many-body phenomena. Here, by in situ tunneling spectroscopy, we show the signatures of superstructure-modulated correlated electron states in epitaxial bilayer graphene (BLG) on 6H-SiC(0001). As the carrier density is locally quasi-‘tuned’ by the superlattice potentials of a $6 \times 6$ interface reconstruction phase, the spectral-weight transfer occurs between the two broad peaks flanking the charge-neutral point. Such a detected non-rigid band shift beyond the single-particle band description implies the existence of correlation effects, probably attributed to the modified interlayer coupling in epitaxial BLG by the $6 \times 6$ reconstruction as in magic-angle BLG by the moiré potentials. Quantitative analysis suggests that the intrinsic interface reconstruction shows a high carrier tunability of $\sim $1/2 filling range, equivalent to the back gating by a voltage of $\sim $70 V in a typical gated BLG/SiO$_{2}$/Si device. The finding in interface-modulated epitaxial BLG with reconstruction phase extends the BLG platform with electron correlations beyond the magic-angle situation, and may stimulate further investigations on correlated states in graphene systems and other van der Waals materials.

Realization of Kondo lattice in superconducting van der Waals materials not only provides a unique opportunity for tuning the Kondo lattice behavior by electrical gating or intercalation, but also is helpful for further understanding the heavy fermion superconductivity. Here we report a low-temperature and vector-magnetic-field scanning tunneling microscopy and spectroscopy study on a superconducting compound (4Hb-TaS$_{2})$ with alternate stacking of 1T-TaS$_{2}$ and 1H-TaS$_{2}$ layers. We observe the quasi-two-dimensional superconductivity in the 1H-TaS$_{2}$ layer with anisotropic response to the in-plane and out-of-plane magnetic fields. In the 1T-TaS$_{2}$ layer, we detect the Kondo resonance peak that results from the Kondo screening of the unpaired electrons in the Star-of-David clusters. We also find that the intensity of the Kondo resonance peak is sensitive to its relative position with the Fermi level, and it can be significantly enhanced when it is further shifted towards the Fermi level by evaporating Pb atoms onto the 1T-TaS$_{2}$ surface. Our results not only are important for fully understanding the electronic properties of 4Hb-TaS$_{2}$, but also pave the way for creating tunable Kondo lattice in the superconducting van der Waals materials.

As a newly developed method for fabricating Josephson junctions, a focused helium ion beam has the advantage of producing reliable and reproducible junctions. We fabricated Josephson junctions with a focused helium ion beam on our 50 nm YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ (YBCO) thin films. We focused on the junction with irradiation doses ranging from 100 to 300 ions/nm and demonstrated that the junction barrier can be modulated by the ion dose and that within this dose range, the junctions behave like superconductor–normal-conductor–superconductor junctions. The measurements of the $I$–$V$ characteristics, Fraunhofer diffraction pattern, and Shapiro steps of the junctions clearly show AC and DC Josephson effects. Our findings demonstrate high reproducibility of junction fabrication using a focused helium ion beam and suggest that commercial devices based on this nanotechnology could operate at liquid nitrogen temperatures.

As a typical hole-doped cuprate superconductor, Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$(Bi2212) carrier doping is mostly determined by its oxygen content. Traditional doping methods can regulate its doping level within the range of hole doping. Here we report the first application of CaH$_{2}$ annealing method in regulating the doping level of Bi2212. By continuously controlling the anneal time, a series of differently doped samples can be obtained. The combined experimental results of x-ray diffraction, scanning transmission electron microscopy, resistance and Hall measurements demonstrate that the CaH$_{2}$ induced topochemical reaction can effectively change the oxygen content of Bi2212 within a very wide range, even switching from hole doping to electron doping. We also found evidence of a low-$T_{\rm c}$ superconducting phase in the electron doping side.

Research interests in recent years have expanded into quantum materials that display novel magnetism incorporating strong correlations, topological effects, and dimensional crossovers. Fe$_{3}$GeTe$_{2}$ represents such a two-dimensional van der Waals platform exhibiting itinerant ferromagnetism with many intriguing properties. Up to date, most electronic transport studies on Fe$_{3}$GeTe$_{2}$ have been limited to its anomalous Hall responses while the longitudinal counterpart (such as magnetoresistance) remains largely unexplored. Here, we report a few unusual transport behaviors on thin flakes of Fe$_{3}$GeTe$_{2}$. Upon cooling to the base temperature, the sample develops a resistivity upturn that shows a crossover from a marginally $-\ln T$ to a ${-}{T}^{1/2}$ dependence, followed by a lower-temperature deviation. Moreover, we observe a negative and non-saturating linear magnetoresistance when the magnetization is parallel or antiparallel to the external magnetic field. The slope of the linear magnetoresistance also shows a nonmonotonic temperature dependence. We deduce an anomalous contribution to the magnetoresistance at low temperatures with a scaling function proportional ${-HT}^{1/2}$, as well as a temperature-independent linear term. Possible mechanisms that could account for our observations are discussed.

We study the spin-$1/2$ two-dimensional Shastry–Sutherland spin model by exact diagonalization of clusters with periodic boundary conditions, developing an improved level spectroscopic technique using energy gaps between states with different quantum numbers. The crossing points of some of the relative (composite) gaps have much weaker finite-size drifts than the normally used gaps defined only with respect to the ground state, thus allowing precise determination of quantum critical points even with small clusters. Our results support the picture of a spin liquid phase intervening between the well-known plaquette-singlet and antiferromagnetic ground states, with phase boundaries in almost perfect agreement with a recent density matrix renormalization group study, where much larger cylindrical lattices were used [J. Yang et al., Phys. Rev. B 105, L060409 (2022)]. The method of using composite low-energy gaps to reduce scaling corrections has potentially broad applications in numerical studies of quantum critical phenomena.

We predict ultrafast modulation of the pure molten metal surface stress fields under the irradiation of the single femtosecond laser pulse through the two-temperature model molecular-dynamics simulations. High-resolution and precision calculations are used to resolve the ultrafast laser-induced anisotropic relaxations of the pressure components on the time-scale comparable to the intrinsic liquid density relaxation time. The magnitudes of the dynamic surface tensions are found being modulated sharply within picoseconds after the irradiation, due to the development of the nanometer scale non-hydrostatic regime behind the exterior atomic layer of the liquid surfaces. The reported novel regulation mechanism of the liquid surface stress field and the dynamic surface tension hints at levitating the manipulation of liquid surfaces, such as ultrafast steering the surface directional transport and patterning.