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<jats:p> <jats:italic>For square-step quantum wells (SSQWs) and graded-step quantum wells (GSQWs), the nonlinear optical rectification (NOR), second harmonic generation (SHG) and third harmonic generation (THG) coefficients under an intense laser field (ILF) are analyzed. The found results indicate that ILF can ensure a vital influence on the shape and height of the confined potential profile of both SSQWs and GSQWs, and alterations of the dipole moment matrix elements and the energy levels are adhered on the profile of the confined potential. According to the results, the potential profile and height of the GSQWs are affected more significantly by ILF intensity compared to SSQWs. These results indicate that NOR, SHG and THG coefficients of SSQWs and GSQWs may be calibrated in a preferred energy range and the magnitude of the resonance peak (RP) by tuning the ILF parameter. It is feasible to classify blue or red shifts in RP locations of NOR, SHG and THG coefficients by varying the ILF parameter. Our results can be useful in investigating new ways of manipulating the opto-electronic properties of semiconductor QW devices</jats:italic>.</jats:p>

<jats:p> <jats:italic>Growth of high-quality single crystals is of great significance for research of condensed matter physics. The exploration of suitable growing conditions for single crystals is expensive and time-consuming, especially for ternary compounds because of the lack of ternary phase diagram. Here we use machine learning (ML) trained on our experimental data to predict and instruct the growth. Four kinds of ML methods, including support vector machine (SVM), decision tree, random forest and gradient boosting decision tree, are adopted. The SVM method is relatively stable and works well, with an accuracy of 81% in predicting experimental results. By comparison, the accuracy of laboratory reaches 36%. The decision tree model is also used to reveal which features will take critical roles in growing processes.</jats:italic> </jats:p>

<jats:p> <jats:italic>Silicon on insulator with highly uniform top Si is fabricated by co-implantation of H<jats:sup>+</jats:sup> and He<jats:sup>+</jats:sup> ions. Compared with the conventional ion-slicing process with H implantation only, the co-implanted specimens whose He depth is deeper than H profile have the top Si layer with better uniformity after splitting. In addition, the splitting occurs at the position that the maximum concentration peak of H overlaps with the secondary concentration peak of He after annealing. It is suggested that the H/He co-implantation technology is a promising approach for fabricating fully depleted silicon on insulator</jats:italic>.</jats:p>

<jats:p> <jats:italic>An intrinsic magnetic topological insulator (TI) is a stoichiometric magnetic compound possessing both inherent magnetic order and topological electronic states. Such a material can provide a shortcut to various novel topological quantum effects but remained elusive experimentally for a long time. Here we report the experimental realization of thin films of an intrinsic magnetic TI, MnBi</jats:italic> <jats:sub>2</jats:sub> <jats:italic>Te</jats:italic> <jats:sub>4</jats:sub> <jats:italic>, by alternate growth of a Bi</jats:italic> <jats:sub>2</jats:sub> <jats:italic>Te</jats:italic> <jats:sub>3</jats:sub> <jats:italic>quintuple layer and a MnTe bilayer with molecular beam epitaxy. The material shows the archetypical Dirac surface states in angle-resolved photoemission spectroscopy and is demonstrated to be an antiferromagnetic topological insulator with ferromagnetic surfaces by magnetic and transport measurements as well as first-principles calculations. The unique magnetic and topological electronic structures and their interplays enable the material to embody rich quantum phases such as quantum anomalous Hall insulators and axion insulators at higher temperature and in a well-controlled way.</jats:italic> </jats:p>

<jats:p> <jats:italic>We report protonation in several compounds by an ionic-liquid-gating method, under optimized gating conditions. This leads to single superconducting phases for several compounds. Non-volatility of protons allows post-gating magnetization and transport measurements. The superconducting transition temperature T</jats:italic> <jats:sub>c</jats:sub> <jats:italic>is enhanced to 43.5 K for FeSe</jats:italic> <jats:sub>0.93</jats:sub> <jats:italic>S</jats:italic> <jats:sub>0.07</jats:sub> <jats:italic>, and 41 K for FeSe after protonation. Superconducting transitions with T</jats:italic> <jats:sub>c</jats:sub> ∼ 15 <jats:italic>K for ZrNCl, ∼7.2 K for 1T-TaS</jats:italic> <jats:sub>2</jats:sub> <jats:italic>, and ∼3.8 K for Bi</jats:italic> <jats:sub>2</jats:sub> <jats:italic>Se</jats:italic> <jats:sub>3</jats:sub> <jats:italic>are induced after protonation. Electric transport in protonated FeSe</jats:italic> <jats:sub>0.93</jats:sub> <jats:italic>S</jats:italic> <jats:sub>0.07</jats:sub> <jats:italic>confirms high-temperature superconductivity. Our</jats:italic> <jats:sup>1</jats:sup> <jats:italic>H nuclear magnetic resonance (NMR) measurements on protonated FeSe</jats:italic> <jats:sub>1−<jats:italic>x</jats:italic> </jats:sub> <jats:italic>S</jats:italic> <jats:sub> <jats:italic>x</jats:italic> </jats:sub> <jats:italic>reveal enhanced spin-lattice relaxation rate</jats:italic> 1/<jats:sup>1</jats:sup> <jats:italic>T</jats:italic> <jats:sub>1</jats:sub> <jats:italic>with increasing x, which is consistent with the LDA calculations that H</jats:italic> <jats:sup>+</jats:sup> <jats:italic>is located in the interstitial sites close to the anions.</jats:italic> </jats:p>

<jats:p> <jats:italic>The first digit law, also known as Benford’s law or the significant digit law, is an empirical phenomenon that the leading digit of numbers from real world sources favors small ones in a form log(1 + 1/d), where d = 1, 2,…, 9. Such a law has been elusive for over 100 years because it has been obscure whether this law is due to the logical consequence of the number system or some mysterious mechanism of nature. We provide a simple and elegant proof of this law from the application of the Laplace transform, which is an important tool of mathematical methods in physics. It is revealed that the first digit law originates from the basic property of the number system, thus it should be attributed as a basic mathematical knowledge for wide applications</jats:italic>.</jats:p>

<jats:p> <jats:italic>Measurement-device-independent quantum key distribution (MDI-QKD) offers a practical way to realize a star-type quantum network. Previous experiments on MDI-QKD networks can only support the point-to-point communication. We experimentally demonstrate a plug-and-play MDI-QKD network which can support the point-to-multipoint communication among three users. Benefiting from the plug-and-play MDI-QKD architecture, the whole network is automatically stabilized in spectrum, polarization, arrival time, and phase reference. The users only need the encoding devices, which means that the hardware requirements are greatly reduced. Our experiment shows that it is feasible to establish a point-to-multipoint MDI-QKD network</jats:italic>.</jats:p>

<jats:p> <jats:italic>The realization of controllable couplings between any two qubits and among any multiple qubits is the critical problem in building a programmable quantum processor (PQP). We present a design to implement these types of couplings in a double-dot molecule system, where all the qubits are connected directly with capacitors and the couplings between them are controlled via the voltage on the double-dot molecules. A general interaction Hamiltonian of n qubits is presented, from which we can derive the Hamiltonians for performing operations needed in building a PQP, such as gate operations between arbitrary two qubits and parallel coupling operations for multigroup qubits. The scheme is realizable with current technology</jats:italic>.</jats:p>

<jats:p> <jats:italic>Due to the obvious deviations of the existing theoretical models from the experimental results of ferroelectric phase transition, a new model is proposed on the basis of the coupling between spontaneous polarization and spontaneous strain in ferroelectrics. The spontaneous polarization and specific heat of ferroelectric phase transition predicted by the model are in better agreement with the corresponding data of triglyceride sulfate, a typical ferroelectric. In addition, the model predicts a new type of ferroelectric in which a phase transition and a phase-like transition coexist</jats:italic>.</jats:p>

<jats:p> <jats:italic>We demonstrate a simple scheme of 6.835 GHz microwave source based on the sub-sampling phase lock loop (PLL). A dielectric resonant oscillator of 6.8 GHz is directly phase locked to an ultra-low phase noise 100 MHz oven controlled crystal oscillator (OCXO) utilizing the sub-sampling PLL. Then the 6.8 GHz is mixed with 35 MHz from an direct digital synthesizer (DDS) which is also referenced to the 100 MHZ OCXO to generate the final 6.835 GHz signal. Benefiting from the sub-sampling PLL, the processes of frequency multiplication, which are usually necessary in the development of a microwave source, are greatly simplified. The architecture of the microwave source is pretty simple. Correspondingly, its power consumption and cost are low. The absolute phase noises of the 6.835 GHz output signal are −47 dBc/Hz, −77 dBc/Hz, −104 dBc/Hz and −121 dBc/Hz at 1 Hz, 10 Hz, 100 Hz and 1 kHz offset frequencies, respectively. The frequency stability limited by the phase noise through the Dick effect is theoretically estimated to be better than 5.0 × 10<jats:sup>−14</jats:sup>τ<jats:sup>1/2</jats:sup> when it is used as the local oscillator of the Rb atomic clocks. This low phase noise microwave source can also be used in other experiments of precision measurement physics</jats:italic>.</jats:p>