The implementation of scalable quantum networks requires photons at the telecom band and long-lived spin coherence. The single Er$^{3+}$ in solid-state hosts is an important candidate that fulfills these critical requirements simultaneously. However, to entangle distant Er$^{3+}$ ions through photonic connections, the emission frequency of individual Er$^{3+}$ in solid-state matrix must be the same, which is challenging because the emission frequency of Er$^{3+}$ depends on its local environment. Herein, we propose and experimentally demonstrate the Stark tuning of the emission frequency of a single Er$^{3+}$ in a Y$_2$SiO$_5$ crystal by employing electrodes interfaced with a silicon photonic crystal cavity. We obtain a Stark shift of 182.9$\pm 0.8$ MHz, which is approximately 27 times of the optical emission linewidth, demonstrating promising applications in tuning the emission frequency of independent Er$^{3+}$ into the same spectral channels. Our results provide a useful solution for construction of scalable quantum networks based on single Er$^{3+}$ and a universal tool for tuning emission of individual rare-earth ions.

We propose a scheme to generate and control supersonic shock waves in a non-resonantly incoherent pumped exciton-polariton condensate, and different types of shock waves can be generated. Under conditions of different initial step waves, the ranges of parameters about various shock waves are determined by the initial incidence function and the cross-interaction between the polariton condensate and the reservoir. In addition, shock waves are successfully found by regulating the incoherent pump. In the case of low condensation rate from polariton to condensate, these results are similar to the classical nonlinear Schrödinger equation, and the effect of saturated nonlinearity resulted from cross interaction is equivalent to the self-interaction between polariton condensates. At high condensation rates, profiles of shock waves become symmetrical due to the saturated nonlinearity. Compared to the previous studies in which the shock wave can only be found in the system with repulsive self-interaction (defocusing nonlinearity), we not only discuss the shock wave in the exciton-polariton condensate system with the repulsive self-interaction, but also find the shock wave in the condensates system with attractive self-interaction. Our proposal may provide a simple way to generate and control shock waves in non-resonantly pumped exciton-polariton systems.

Random numbers are one of the key foundations of cryptography. This work implements a discrete quantum random number generator (QRNG) based on the tunneling effect of electrons in an avalanche photo diode. Without any post-processing and conditioning, this QRNG can output raw sequences at a rate of 100 Mbps. Remarkably, the statistical min-entropy of the 8,000,000 bits sequence reaches 0.9944 bits/bit, and the min-entropy validated by NIST SP 800-90B reaches 0.9872 bits/bit. This metric is currently the highest value we have investigated for QRNG raw sequences. Moreover, this QRNG can continuously and stably output raw sequences with high randomness over extended periods. The system produced a continuous output of 1,174 Gbits raw sequence for a duration of 11,744 s, with every 8 Mbits forming a unit to obtain a statistical min-entropy distribution with an average value of 0.9892 bits/bit. The statistical min-entropy of all data (1,174 Gbits) achieves the value of 0.9951 bits/bit. This QRNG can produce high-quality raw sequences with good randomness and stability. It has the potential to meet the high demand in cryptography for random numbers with high quality.

Superconducting transmon qubits with fixed frequencies are widely used in many applications due to their advantages of better coherence and less control lines compared to the frequency tunable qubits. However, any uncontrolled interactions with the qubits such as the two-level systems could lead to adverse impacts, degrading the qubit coherence and inducing crosstalk. To mitigate the detrimental effect from uncontrolled interactions between qubits and defect modes in fixed-frequency transmon qubits, we propose and demonstrate an active approach using an off-resonance microwave drive to dress the qubit and to induce the ac-Stark shift on the qubit frequency. We show experimentally that the qubit frequency can be tuned well away from the defect mode so that the impact on qubit coherence is greatly reduced while maintaining the universal controls of the qubit initialization, readout, and single-qubit gate operations. Our approach provides an effective way for tuning the qubit frequency and suppressing the detrimental effect from the defect modes that happen to be located close to the qubit frequency.

We examine the deep learning technique referred to as the physics-informed neural network method for approximating the nonlinear Schrödinger equation under considered parity-time symmetric potentials and for obtaining multifarious soliton solutions. Neural networks to found principally physical information are adopted to figure out the solution to the examined nonlinear partial differential equation and to generate six different types of soliton solutions, which are basic, dipole, tripole, quadruple, pentapole, and sextupole solitons we consider. We make comparisons between the predicted and actual soliton solutions to see whether deep learning is capable of seeking the solution to the partial differential equation described before. We may assess whether physics-informed neural network is capable of effectively providing approximate soliton solutions through the evaluation of squared error between the predicted and numerical results. Moreover, we scrutinize how different activation mechanisms and network architectures impact the capability of selected deep learning technique works. Through the findings we can prove that the neural networks model we established can be utilized to accurately and effectively approximate the nonlinear Schrödinger equation under consideration and to predict the dynamics of soliton solution.

Numerical research is conducted to investigate the effects of plasma boundary shape on the tearing mode triggering explosive bursts in toroidal tokamak plasmas. In this work, $m/n=2/1$ mode is responsible for the triggering of the explosive burst. Plasma boundary shape can be adjusted via the adjustment of the parameters triangularity ${\delta}$ and elongation ${\kappa}$. The investigations are conducted both under low $\beta$ (close to zero) and under finite $\beta$ regimes. In the low $\beta$ regime, triangularity and elongation both have stabilizing effect on the explosive burst, and the stabilizing effect of elongation is stronger. Under a large elongation (${\kappa =2.0}$), the elongation effect can evidently enhance the stabilizing effect in a positive triangularity regime, but barely affects the stabilizing effect in a negative triangularity regime. In the finite $\beta$ regime, the explosive burst is delayed in comparison with that in the low $\beta$ regime. Similar to the low $\beta$ cases, the effects of triangularity and elongation both are stabilizing. Under a large elongation (${\kappa =2.0}$), the elongation effect can evidently enhance the stabilizing effect on the explosive burst in a positive triangularity regime, but impair the stabilizing effect in a negative triangularity regime. The explosive burst disappears in the large triangularity case (${\delta =0.5}$), indicating that the explosive burst can be effectively prevented in experiments via carefully adjusting plasma boundary shape. Moreover, strong magnetic stochasticity appears in the negative triangularity case during the nonlinear phase.

Using a swarm intelligence structure search method combining with first-principles calculations, three new structures of Zn–I and Hg–I compounds are discovered and pressure-composition phase diagrams are determined. An interesting phenomenon is found, that is, the compounds that are stable at 0 GPa in both systems will decompose into their constituent elements under certain pressure, which is contrary to the general intuition that pressure always makes materials more stability and density. A detailed analysis of the decomposition mechanism reveals the increase of formation enthalpy with the increase of pressure due to contributions from both $\Delta U$ and $\Delta [PV]$. Pressure-dependent studies of the $\Delta V$ demonstrate that denser materials tend to be stabilized at higher pressures. Additionally, charge transfer calculations show that external pressure is more effective in regulating the ionic bond of Hg–I, resulting in a lower decomposition pressure for HgI$_{2}$ than for ZnI$_{2}$. These findings have important implications for designs and syntheses of new materials, as they challenge the conventional understanding on how pressure affects stability.

The nickel-based superconductivity provides a fascinating new platform to explore high-$T_{\rm c}$ superconductivity. As the infinite-layer nickelates are obtained by removing the apical oxygens from the precursor perovskite phase, the crystalline quality of the perovskite phase is crucial in synthesizing high quality superconducting nickelates. Especially, cation-related defects, such as the Ruddlesden–Popper-type (RP-type) faults, are unlikely to disappear after the topotactic reduction process and should be avoided during the growth of the perovskite phase. Herein, using reactive molecular beam epitaxy, we report the atomic-scale engineering of the interface structure and demonstrate its impact in reducing crystalline defects in Nd-based nickelate/SrTiO$_{3}$ heterostructures. A simultaneous deposition of stoichiometric Nd and Ni directly on SrTiO$_{3}$ substrates results in prominent Nd vacancies and Ti diffusion at the interface and RP-type defects in nickelate films. In contrast, inserting an extra [NdO] monolayer before the simultaneous deposition of Nd and Ni forms a sharp interface and greatly eliminates RP-type defects in nickelate films. A possible explanation related to the polar discontinuity is also discussed. Our results provide an effective method to synthesize high-quality precursor perovskite phase for the investigation of the novel superconductivity in nickelates.

The emergent van der Waals magnetic material is a promising component for spintronic devices with novel functionalities. Here, we report a transition of negative-to-positive magnetoresistance in Fe$_{3}$GeTe$_{2}$/Cr$_{2}$Ge$_{2}$Te$_{6}$/ Fe$_{3}$GeTe$_{2}$ van der Waals all-magnetic tunnel junctions with increasing the applied bias voltage. A negative magnetoresistance is observed first in Fe$_{3}$GeTe$_{2}$/Cr$_{2}$Ge$_{2}$Te$_{6}$/Fe$_{3}$GeTe$_{2}$ tunnel junctions, where the resistance with antiparallel aligned magnetization of two Fe$_{3}$GeTe$_{2}$ electrodes is lower than that with parallel alignment, which is due to the opposite spin polarizations of two Fe$_{3}$GeTe$_{2}$ electrodes. With the bias voltage increasing, the spin polarization of the biased Fe$_{3}$GeTe$_{2}$ electrode is changed so that the spin orientations of two Fe$_{3}$GeTe$_{2}$ electrodes are the same. Our experimental observations are supported by the calculated spin-dependent density of states for Fe$_{3}$GeTe$_{2}$ electrodes under a finite bias. The significantly bias voltage-dependent spin transport properties in van der Waals magnetic tunnel junctions open a promising route for designing electrical controllable spintronic devices based on van der Waals magnets.

Two-dimensional van der Waals magnetic materials are of great current interest for their promising applications in spintronics. Using density functional theory calculations in combination with the maximally localized Wannier functions method and the magnetic anisotropy analyses, we study the electronic and magnetic properties of MnPSe$_3$ monolayer. Our results show that it is a charge transfer antiferromagnetic (AF) insulator. For this Mn$^{2+}$ $3d^5$ system, although it seems straightforward to explain the AF ground state using the direct exchange, we find that the nearly 90$^\circ$ Mn–Se–Mn charge transfer type superexchange plays a dominant role in stabilizing the AF ground state. Moreover, our results indicate that, although the shape anisotropy favors an out-of-plane spin orientation, the spin-orbit coupling (SOC) leads to the experimentally observed in-plane spin orientation. We prove that the actual dominant contribution to the magnetic anisotropy comes from the second-order perturbation of the SOC, by analyzing its distribution over the reciprocal space. Using the AF exchange and anisotropy parameters obtained from our calculations, our Monte Carlo simulations give the Néel temperature $T_{\rm N}=47$ K for MnPSe$_3$ monolayer, which agrees with the experimental 40 K. Furthermore, our calculations show that under a uniaxial tensile (compressive) strain, Néel vector would be parallel (perpendicular) to the strain direction, which well reproduces the recent experiments. We also predict that $T_{\rm N}$ would be increased by a compressive strain.

We experimentally investigate nonlinear Hall effect as zero-frequency and second-harmonic transverse voltage responses to ac electric current for topological semimetal GeTe. A thick single-crystal GeTe flake is placed on the Si/SiO$_2$ substrate, where the p-doped Si layer serves as a gate electrode. We confirm that electron concentration is not gate-sensitive in thick GeTe flakes due to the gate field screening by bulk carriers. In contrast, by transverse voltage measurements, we demonstrate that the nonlinear Hall effect shows pronounced dependence on the gate electric field at room temperature. Since the nonlinear Hall effect is a direct consequence of a Berry curvature dipole in topological media, our observations indicate that Berry curvature can be controlled by the gate electric field. This experimental observation can be understood as a result of the known dependence of giant Rashba splitting on the external electric field in GeTe. For possible applications, the zero-frequency gate-controlled nonlinear Hall effect can be used for the efficient broad-band rectification.

A new two-dimensional allotrope of carbon known as biphenylene has been synthesized. Building on previous research investigating the superconductivity of octagraphene with a square-octagon structure, we conduct a systematic study on possible superconductivity of biphenylene with partial square-octagon structure. First-principle calculations are used to fit the tight-binding model of the material and to estimate its superconductivity. We find that the conventional superconducting transition temperature $T_{\rm c}$ based on electron-phonon interaction is 3.02 K, while the unconventional $T_{\rm c}$ primarily caused by spin fluctuation is 1.7 K. We hypothesize that the remaining hexagonal $C_6$ structure of biphenylene may not be conducive to the formation of perfect Fermi nesting, leading to a lower $T_{\rm c}$. The superconducting properties of this material fall between those of graphene and octagraphene, and it lays a foundation for achieving high-temperature superconductivity in carbon-based materials.

As a prototypical half-metallic ferromagnet, La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) has been extensively studied due to its versatile physical properties and great potential in spintronic applications. However, the weak perpendicular magnetic anisotropy (PMA) limits the controllability and detection of magnetism in LSMO, thus hindering the realization of oxide-based spintronic devices with low energy consumption and high integration level. Motivated by this challenge, we develop an experimental approach to enhance the PMA of LSMO epitaxial films. By cooperatively introducing 4$d$ Ru doping and a moderate compressive strain, the maximum uniaxial magnetic anisotropy in Ru-doped LSMO can reach $3.0 \times 10^{5}$ J/m$^{3}$ at 10 K. Furthermore, we find a significant anisotropic magnetoresistance effect in these Ru-doped LSMO films, which is dominated by the strong PMA. Our findings offer an effective pathway to harness and detect the orientations of magnetic moments in LSMO films, thus promoting the feasibility of oxide-based spintronic devices, such as spin valves and magnetic tunnel junctions.

Light-induced ultrafast spin dynamics in materials is of great importance for developments of spintronics and magnetic storage technology. Recent progresses include ultrafast demagnetization, magnetic switching, and magnetic phase transitions, while the ultrafast generation of magnetism is hardly achieved. Here, a strong light-induced magnetization (up to $0.86\mu_{\scriptscriptstyle{\rm B}}$ per formula unit) is identified in non-magnetic monolayer molybdenum disulfide (MoS$_{2}$). With the state-of-the-art time-dependent density functional theory simulations, we demonstrate that the out-of-plane magnetization can be induced by circularly polarized laser, where chiral phonons play a vital role. The phonons strongly modulate spin-orbital interactions and promote electronic transitions between the two conduction band states, achieving an effective magnetic field $\sim$ $380$ T. Our study provides important insights into the ultrafast magnetization and spin-phonon coupling dynamics, facilitating effective light-controlled valleytronics and magnetism.

We demonstrate the use of an infrared modulated photoluminescence (PL) method based on a step-scan Fourier-transform infrared spectrometer to analyze intersubband transition (ISBT) of InGaAs/InAlAs quantum cascade detector (QCD) structures. By configuring oblique and parallel excitation geometries, high signal-to-noise ratio PL spectra in near-to-far-infrared region are measured. With support from numerical calculations based on the ${\boldsymbol k}$$\cdot$${\boldsymbol p}$ perturbation theory, the spectra is attributed to intraband and interband transitions of InGaAs/InAlAs QCD structures. Temperature evolution results show that the $k$-dependent transitions caused by longitudinal optical phonon-assisted scattering (Fröhlich interaction) plays an important role in the ISBT. These results suggest that this infrared modulated-PL method has great potential in characterizing QCD devices and conducting performance diagnostics.

A novel thermal emitter with metal-insulator-metal design is proposed to realize efficient daytime radiative cooling. It can achieve ultrahigh absorption of 99.67% in the first atmospheric window and strong reflection of 94.86% in solar band. Analysis on the cooling performance with different real and imaginary parts of refractive index is carried out to provide a guide line in the material choice. As a case study, three inorganic materials are substituted to get enhanced absorption and it is verified that the refractive index matching is desirable to obtain high absorption. In addition, such high emissivity persists under different incident angles in both TE and TM modes. A net cooling power of 96.39 W/m$^{2}$ is achieved in the daytime with the incorporation of convection coefficients. Finally, this thermal emitter achieves an average temperature drop of 5.1 ℃ based on the solution of conduction equation at 300 K. Therefore, our design with an excellent cooling ability can further bolster development in managements of radiative cooling or thermal radiation.

G-quadruplex (G4) is one of the higher-order DNA structures in guanine-rich sequences which are widely distributed across the genome. Due to their presence in oncogenic promoters and telomeres, G4 DNA structures become the novel targets in anticancer drug designs. Curaxin CBL0137, as an important candidate anticancer drug, can effectively inhibit the growth of multiple cancers. Although there is evidence that anticancer activity of curaxin is associated with its ability to bind DNA and to change the DNA topology, its therapeutic target and the underlying anti-cancer mechanism are still unclear. Here we show, for the first time, that curaxin CBL0137 induces G4 folding from anti-parallel to parallel structures, by single-molecule fluorescence resonance energy transfer technique. More importantly, we find that curaxin CBL0137 promotes G4 folding as well as stabilizes the folded G4 structures with long loops, giving a novel insight into effects of curaxin CBL0137 on DNA structures. Our work provides new ideas for the therapeutic mechanism of curaxin CBL0137 and for designs of new G4-targeting anticancer drugs.