Coherence is a key resource in quantum information science. Exactly understanding and controlling the variation of coherence are vital for implementation in realistic quantum systems. Using $P$-representation of density matrix, we obtain the analytical solution of the master equation for the classical states in the non-Markovian process and investigate the coherent dynamics of Gaussian states. It is found that quantum coherence can be preserved in such a process if the coupling strength between system and environment exceeds a threshold value. We also discuss the characteristic function of the Gaussian states in the non-Markovian process, which provides an inevitable bridge for the control and operation of quantum coherence.

Based on a conventional torsion pendulum, we develop a forced oscillation viscometer with ultra-high viscosity sensitivity of $2\times10^{-7}$ Pa$\cdot$s working at frequencies near the resonance. The viscosity is achieved by exploiting the phase lag for the angle displacement behind the torque, instead of the resonant curve, i.e., the variation of angle displacement amplitude versus frequency. The general formula for the measurement of the visco-elasticity of complex fluids is also presented. With such precision it is easy to measure tiny change in viscosity result from circumstantial influences. Deionized water and two kinds of NaCl aqueous solutions are chosen to demonstrate the performance of our home-made torsion pendulum-based viscometer.

Axion-like particles (ALPs) are often defined as relatively light pseudoscalar particles and appear in many extensions of the Standard Model. Taking into account constraints on the free parameters from existing searches and explaining the $g$-2 deviation, we consider the contributions of ALPs with mass in the range of 1.5 GeV$\, < m_{a} < m_{h}-m_{Z}$ to the exclusive Higgs decays $h \rightarrow PZ$ and $h \rightarrow P\ell^{+} \ell^{-}$ with $P$ being the pseudoscalar mesons $\pi^{0}$, $\eta$, $\eta'$, $\eta_{c}$ and $\eta_{b}$ in a model-independent approach. We find that, in most of the parameter space range, the contributions of ALP to these decay processes are very small, while in the case of the ALP mass $m_{a}$ approximately equaling the meson mass $m_{P}$, the contributions are significantly large.

We investigate the level structure and $E2$, $M1$ electromagnetic transition properties in an even–even $^{96}$Mo nucleus within the framework of the proton–neutron interacting boson model (IBM-2). The calculated results of the IBM-2 can reproduce the recent new experimental data on $^{96}$Mo both qualitatively and quantitatively. It is found that both shape coexistence and mixed-symmetry states in $^{96}$Mo can be simultaneously described very well with the IBM-2 by taking into account that the relative energy of $d$ neutron bosons is different from that of proton bosons.

The isoscalar giant monopole resonances (ISGMRs) of hypernuclei $^{42}_{{\Lambda}{\Lambda}}$Ca, $^{122}_{{\Lambda}{\Lambda}}$Sn, and $^{210}_{{\Lambda}{\Lambda}}$Pb are investigated using a fully self-consistent Skyrme–Hartree–Fock plus random phase approximation method. The Skyrme-type forces, SGII, No.5 and S${\Lambda}{\Lambda}$1, are adopted to describe the nucleon–nucleon, ${\Lambda}$ hyperon–nucleon and ${\Lambda}$ hyperon–${\Lambda}$ hyperon (${\Lambda} {\Lambda}$) interactions, respectively. For a given hyperon fraction, we find that effects of ${\Lambda} {\Lambda}$ interaction on the properties of infinite symmetric nuclear matter and finite hypernuclei are very small. The ISGMR strengths are shifted to the high energy region when two ${\Lambda}$ are added into normal nuclei. The changes are from two parts, one is due to the mean field calculations, and the other is from the residual interaction associated with ${\Lambda}$ hyperons. The constrained energies are increased by about 0.5–0.7 MeV, which consequently enhances the effective incompressibility modulus of hypernuclei.

We study the influence of the phase noises of far detuning single frequency lasers on the lifetime of Bose–Einstein condensation (BEC) of $^{87}$Rb in an optical dipole trap. As a comparison, we shine a continuous-wave single-frequency Ti:sapphire laser, an external-cavity diode laser and a phase-locked diode laser on BEC. We measure the heating and lifetime of BEC in two different hyperfine states: $|F=2,m_{F}=2\rangle$ and $|F=1,m_{F}=1\rangle$. Due to the narrow linewidth and small phase noise, the continuous-wave single-frequency Ti:sapphire laser has less influence on the lifetime of $^{87}$Rb BEC than the external-cavity diode laser. To reduce the phase noise of the external-cavity diode laser, we use an optical phase-locked loop for the external-cavity diode laser to be locked on a Ti:sapphire laser. The lifetime of BEC is increased when applying the phase-locked diode laser in contrast with the external-cavity diode laser.

We demonstrate a diode pumped Yb:LuVO$_{4}$ laser that can be passively Q-switched by a Cr$^{4+}$:YAG saturable absorber having an initial transmission as high as 99.3%. A maximum pulsed output power of 2.35 W is generated at a repetition rate of 285.7 kHz, approaching or very near the intrinsic upper limit imposed by the recovery time of the Cr$^{4+}$:YAG saturable absorber, and the resulting pulse energy, duration and peak power are, respectively, 8.2 $\mu$J, 39.2 ns and 0.209 kW.

A passively Q-switched Nd:YVO$_{4}$ laser at 1064 nm is demonstrated based on a gold nanotriangle saturable absorber (GNT SA). Under a pump power of 3.82 W, the maximum average output power of 218 mW is achieved, corresponding to a slope efficiency of 12.9%. The minimum pulse width is 165 ns and the maximum pulse repetition rate is 300 kHz at the pump power of 3.48 W. Our results prove that the GNT SA is a promising saturable absorber for near-infrared lasers.

We analytically investigate nonlinear tearing modes with the anomalous electron viscosity or, as it is normally called, hyper-resistivity. In contrast to the flux average method used by previous work, we employ the standard singular perturbation technique and a quasilinear method to obtain the time evolution equation of tearing modes. The result that the magnetic flux grows with time in a scaling as $t^{2/3}$ demonstrates that nonlinear tearing modes with the hyper-resistivity effect alone have a weaker dependence on time than that of the corresponding resistive case.

Based on the matching rules for squares and rhombuses, we study the self-similar transformation and the vertex configurations of the Ammann–Beenker tiling. The structural properties of the configurations and their relations during the self-similar transformation are obtained. Our results reveal the distribution correlations of the configurations, which provide an intuitive understanding of the octagonal quasi-periodic structure and also give implications for growing perfect quasi-periodic tiling according to the local rules.

The influence of the pressure transmission medium (PTM) on the excitonic interband transitions in monolayer tungsten diselenide (WSe$_{2}$) is investigated using photoluminescence (PL) spectra under hydrostatic pressure up to 5 GPa. Three kinds of PTMs, condensed argon (Ar), 1:1 n-pentane and isopentane mixture (PM), and 4:1 methanol and ethanol mixture (MEM, a PTM with polarity), are used. It is found that when either Ar or PM is used as the PTM, the PL peak of exciton related to the direct $K$–$K$ interband transition shows a pressure-induced blue-shift at a rate of 32$\pm$4 or 32$\pm$1 meV/GPa, while it turns to be 50$\pm$9 meV/GPa when MEM is used as the PTM. The indirect ${\it \Lambda}$–$K$ interband transition presents almost no shift with increasing pressure up to approximately 5 GPa when Ar and PM are used as the PTM, while it shows a red-shift at the rate of $-$17$\pm$7 meV/GPa by using MEM as the PTM. These results reveal that the optical interband transitions of monolayer WSe$_{2}$ are very sensitive to the polarity of the PTM. The anomalous pressure coefficient obtained using the polar PTM of MEM is ascribed to the existence of hydrogen-like bonds between hydroxyl in MEM and Se atoms under hydrostatic pressure.

Nanocomposite ZrCN films consisting of nanocrystalline ZrCN grains embedded in nitrogen-doped amorphous carbon film are deposited by filtered cathodic vacuum arc technology under different bias voltages ranging from 50 to 400 V. The influence of bias voltage on the characterization and the mechanical properties of the ZrCN films are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and nano-indentation. The bias voltage has a subtle effect on the ZrCN grain size, which is around 9.5 nm and keeps almost constant. A slight increase of the bias voltage induces a relatively high $sp^{3}$ fraction about 40% in N-doped amorphous C films but leads to the graphitization of the films under a higher voltage. The best mechanical property of the ZrCN film with the hardness of 41 GPa is obtained under the bias voltage of 200 V, indicating the positive effect of slight increase of ion bombardment on the hardness of the films.

2H- and 1T$'$-phase monolayer MoTe$_{2}$ films on highly oriented pyrolytic graphite are studied using scanning tunneling microscopy and spectroscopy (STM/STS). The phase transition of MoTe$_{2}$ can be controlled by a post-growth annealing process, and the intermediate state during the phase transition is directly observed by STM. For 2H-MoTe$_{2}$, inversion domain boundaries are presented as bright lines at high sample bias, but as dark lines at lower sample bias. The $dI/dV$ mappings reveal the distinct distributions of electronic states between domain boundaries and interiors of domains. It should be noted that a $2\times2$ periodic structure is clearly discernable inside the domains, where the STS measurement shows a small dip of size $\sim$150 meV at the vicinity of the Fermi level, indicating that the $2\times2$ periodic structure may be an incommensurate charge density wave. Moreover, a $4\times4$ periodic structure appears in 2H-MoTe$_{2}$ grown at a higher substrate temperature.

Surface structures and properties of Sn islands grown on superconducting substrate 2H-NbSe$_{2}$(0001) are studied using low temperature scanning tunneling microscopy or spectroscopy. The pure face-centered cubic (fcc) structure of Sn surface is obtained. Superconductivity is also detected on the fcc-Sn(111) surface, and the size of superconducting gap on the Sn surface is nearly the same as that on the superconducting substrate. Furthermore, phase transition occurs from fcc-Sn(111) to $\beta$-Sn(001) by keeping the sample at room temperature for a certain time. Due to the strain relaxation on the $\beta$-Sn islands, both the in-plane unit cell and out-of-plane structures distort, and the height of surface atoms varies periodically to form a universal ripple structure.

The electronic transport properties of a molecular junction based on doping tailoring armchair-type graphene nanoribbons (AGNRs) with different widths are investigated by applying the non-equilibrium Green's function formalism combined with first-principles density functional theory. The calculated results show that the width and doping play significant roles in the electronic transport properties of the molecular junction. A higher current can be obtained for the molecular junctions with the tailoring AGNRs with $W=11$. Furthermore, the current of boron-doped tailoring AGNRs with widths $W=7$ is nearly four times larger than that of the undoped one, which can be potentially useful for the design of high performance electronic devices.

We successfully synthesize a series of polycrystalline CeRu$_{x}$Fe$_{1-x}$Ge$_{3}$ ($0\leq x\leq 0.5$) samples, which are characterized using powder x-ray diffraction, resistivity and specific heat measurements. The expansion of the lattice constants with increasing $x$ demonstrates the successful doping of Ru into the CeFeGe$_{3}$ lattice. Upon doping, it is found that the temperature up to which Landau–Fermi liquid behavior is observed in the resistivity is reduced. Meanwhile, there is also a pronounced increase in the resistivity coefficient and residual resistivity, as well as a clear upturn in $C/T$ at low temperatures, suggesting that Ru doping may tune the system towards a quantum critical point.

Using the natural orbitals renormalization group (NORG) method, we investigate the screening of the local spin of an Anderson impurity interacting with the helical edge states in a quantum spin Hall insulator. It is found that there is a local spin formed at the impurity site and the local spin is completely screened by electrons in the quantum spin Hall insulator. Meanwhile, the local spin is screened dominantly by a single active natural orbital. We then show that the Kondo screening mechanism becomes transparent and simple in the framework of the natural orbitals formalism. We project the active natural orbital respectively into real space and momentum space to characterize its structure. We confirm the spin-momentum locking property of the edge states based on the occupancy of a Bloch state on the edge to which the impurity couples. Furthermore, we study the dynamical property of the active natural orbital represented by the local density of states, from which we observe the Kondo resonance peak.

We study the effects of infrared radiation on a two-dimensional Bardeen–Cooper–Schrieffer superconductor coupled with a normal metal substrate through a tunneling barrier. The phase transition is analyzed by inspecting the stability of the system against perturbations of pairing potentials. We find an oscillating gap phase with a frequency not directly related to the radiation frequency, but instead resulting from the asymmetry of electron density of states of the system as well as the tunneling amplitude. When such a superconductor is in contact with another superconductor, gives rise to an unusual alternating Josephson current.

We present a conceptual configuration of a high-temperature superconducting (HTS) magnet made from REBCO (Re=Rare Earth, B=Barium, C=Copper, O=Oxide) annular plates, called a Bitter-like HTS magnet, which can operate in persistent current mode without joint resistance and can be excited by a flux pump and without current leads and a persistent power supply. An REBCO annular magnet which can generate 1.5 T corresponding to the operating current density 80% of critical current density of the magnet at an operating temperature of 65 K is conceptually designed. Then the thermal stability of the magnet is numerically simulated by Comsol software. When a piece of REBCO annular plate quenches, the maximum released energy is its stored energy because each REBCO annular plate in the Bitter-like magnet is in parallel. To calculate the stored energy in the REBCO annular plate, the inductance of every annular plate, including self-inductance and mutual inductance, is calculated. Compared with the minimum quench energy (MQE) and stored energy in one REBCO annular plate, the stored energy in one REBCO annular plate is always smaller than the MQE, and the REBCO annular plate will not be damaged even though the stored energy in the REBCO annular plate is fully released, which indicates that this 1.5 T Bitter-like magnet has the property of self-protection.

The parent compounds of the high-temperature cuprate superconductors are Mott insulators. It has been generally agreed that understanding the physics of the doped Mott insulators is essential to understanding the mechanism of high temperature superconductivity. A natural starting point is to elucidate the basic electronic structure of the parent compound. Here we report comprehensive high resolution angle-resolved photoemission measurements on Ca$_2$CuO$_2$Cl$_2$, a Mott insulator and a prototypical parent compound of the cuprates. Multiple underlying Fermi surface sheets are revealed for the first time. The high energy waterfall-like band dispersions exhibit different behaviors near the nodal and antinodal regions. Two distinct energy scales are identified: a d-wave-like low energy peak dispersion and a nearly isotropic lower Hubbard band gap. These observations provide new information of the electronic structure of the cuprate parent compound, which is important for understanding the anomalous physical properties and superconductivity mechanism of the high temperature cuprate superconductors.

High-surface-area ZnO nanosheets are prepared using a template-assisted hydrothermal method. A saturation moment as high as 0.02 emu/g is obtained for the ZnO nanosheets. Both photoluminescence spectroscopy and x-ray photoelectron spectroscopy demonstrate the existence of abundant oxygen vacancies on the surfaces of the nanosheets. In addition, the oxygen vacancy concentration increases with an increasing nanosheet surface area. The results show that the origin of the room-temperature ferromagnetism is closely related with a large surface area and oxygen vacancies of the nanosheets. This finding suggests that the high-surface-area ZnO nanosheets are promising to be applied to spintronic devices.

FePt nanoparticles in mesoporous silica are fabricated by a simple stepwise synthesis strategy. A pre-annealing temperature-dependent coercivity-ageing effect in FePt nanoparticles is observed at room temperature. For face-centered cubic (fcc) structured FePt nanoparticles, the ageing effect is sensitive to the pre-annealing temperature, especially when the temperature is close to the phase-transition. The special magnetic behavior of FePt nanoparticles reveals that the physical properties gradually change between fcc and face-centered tetragonal structures, and will deepen our understanding of the mechanism of such magnetism in FePt nanoparticles.

Four kinds of Au nanorods (NRs) with different aspect ratios are designed to adjust the relationship between resonance energy level of longitudinal (L) and transverse (T) modes. During the femto-second $Z$-scan experiments, huge saturable absorption phenomena are observed while the energy level T is located between one to two times of the energy level L. This means that the energy may transfer between longitudinal and transverse energy levels in the same and/or different Au NRs. It effectively depresses the production of revised saturated absorption and increases the saturable absorption efficiency. This method is significant for the preparation of high-efficiency saturable absorption devices.

Nano-floating gate memory devices with ZnO nano-crystals as charge storage layers are fabricated, and the influence of post-deposition annealing temperature and thickness of the ZnO layer are investigated. Atomic force microscopy and scanning electron microscopy reveal the morphology of discrete ZnO nano-crystals. For capacitance-voltage measurements, it is found that the memory device with 1.5 nm ZnO and annealed at 700$^{\circ}\!$C shows a larger memory window of 4.3 V (at $\pm$6 V) and better retention characteristics than memory devices with 2.5 nm ZnO or annealed at other temperatures. These results indicate that the nano-floating gate memory with ZnO nano-crystals can obtain good trade-off memory properties.

Monte Carlo simulations are performed on the dosimetric effect of metallic nanoparticles in a clinical proton irradiation. With an in-water hitting model of a single nanoparticle, the secondary electrons dose, deposited around the particle surface, is calculated for the proton irradiations in a typical spread-out Bragg peak. The dose enhancement, as the ratio of electron doses from the target particle and background water, is evaluated for the dependence on the depth of hitting, particle size, elements, coating material and thickness. The results indicate a significant dose enhancement on the particle surface within $\sim$100 nm, but a fast decay in further distance. The dose enhancement presents a consistency along the spread-out Bragg peak, a positive dependence on both the particle size and electron density, but a strong attenuation by surface coating. Particle cluster may increase the individual dose enhancement by electron crossfire, but is only noticeable in a compact case. The dose enhancement potentiates a radiosensitization use of metallic nanoparticles in clinical proton therapy, but challenging meanwhile with the narrow range of enhancement effect.