Solitonic characteristics are revealed in the diffusion process of a hump or a notch wave packet in a one-dimensional Bose–Einstein condensate. By numerically solving the time-dependent Gross–Pitaevskii equation, we find completely different spreading behavior for attractive or repulsive condensates. For the attractive condensate, a series of bright solitons are continuously generated one after another at the wave front and they nearly stay at the positions where they are generated in the whole diffusion process. In contrast, for the repulsive condensate, the initial wave packet splits at the beginning into a series of grey solitons that travel at different velocities. The moving velocity of the grey soliton depends on nonlinear interaction strength, as well as the shape of a particular grey soliton.

We propose a new exponential shape function in wormhole geometry within modified gravity. The energy conditions and the equation-of-state parameter are obtained. The radial and tangential null energy conditions, and also the weak energy condition are validated, which indicates the absence of exotic matter due to modified gravity allied with such a new proposal.

Soliton molecules were first discovered in optical systems and are currently a hot topic of research. We obtain soliton molecules of the (2+1)-dimensional fifth-order KdV system under a new resonance condition called velocity resonance in theory. On the basis of soliton molecules, asymmetric solitons can be obtained by selecting appropriate parameters. Based on the $N$-soliton solution, we obtain hybrid solutions consisting of soliton molecules, lump waves and breather waves by partial velocity resonance and partial long wave limits. Soliton molecules, and some types of special soliton resonance solutions, are stable under the meaning that the interactions among soliton molecules are elastic. Both soliton molecules and asymmetric solitons obtained may be observed in fluid systems because the fifth-order KdV equation describes the ion-acoustic waves in plasmas, shallow water waves in channels and oceans.

We report the realization of quantum logic spectroscopy on the $^1\!S_0\rightarrow {}^3\!P_0$ clock transition of a single $^{27}$Al$^+$ ion. This ion is trapped together with a $^{40}$Ca$^+$ ion in a linear Paul trap, coupled by Coulomb repulsion, which provides sympathetic Doppler laser cooling and also the means for internal state detection of the clock state of the $^{27}$Al$^+$ ion. A repetitive quantum nondemolition measurement is performed to improve the fidelity of state detection. These techniques are applied to obtain clock spectroscopy at approximately 45 Hz. We also perform the preliminary locking on the $^1\!S_0\rightarrow {}^3\!P_0$ clock transition. Our work is a fundamental step that is necessary toward obtaining an ultra-precision quantum logic clock based on $^{40}$Ca$^+$-$^{27}$Al$^+$ ions.

Boron carbide (B$_{4}$C) coatings have high reflectivity and are widely used as mirrors for free-electron lasers in the x-ray range. However, B$_{4}$C coatings fabricated by direct-current magnetron sputtering show a strong compressive stress of about $-3$ GPa. By changing the argon gas pressure and nitrogen-argon gas mixing ratio, we are able to reduce the intrinsic stress to less than $-1$ GPa for a 50-nm-thick B$_{4}$C coating. It is found that the stress in a coating deposited at 10 mTorr is $-0.69$ GPa, the rms roughness of the coating surface is 0.53 nm, and the coating reflectivity is 88%, which is lower than those of coatings produced at lower working pressures. When the working gas contains 8% nitrogen and 92% argon, the B$_{4}$C coating shows not only $-1.19$ GPa stress but also a low rms roughness of 0.16 nm, and the measured reflectivity is 93% at the wavelength of 0.154 nm.

A high-$Q$ quartz crystal microbalance (QCM) sensor with a fundamental resonance frequency of 210 MHz is developed based on inverted mesa technology. The mass sensitivity reaches $5.332\times 10^{17}$ Hz/kg at the center of the electrode, which is 5–7 orders of magnitude higher than the commonly used 5 MHz or 10 MHz QCMs (their mass sensitivity is $10^{10}$–$10^{12}$ Hz/kg). This mass sensitivity is confirmed by an experiment of plating 1-ng rigid aluminium films on the surface of the QCM sensor. By comparing the changes in QCM equivalent parameters before and after coating the aluminum films, it is found that the QCM sensor maintains the high-$Q$ characteristics of the quartz crystal while the mass sensitivity is significantly improved. Therefore, this QCM sensor may be used as a promising analytical tool for applications requiring high sensitivity detection.

We report on an injection seeded 1 kHz single frequency pulsed Nd:YAG ring laser with pulse energy of 5.2 mJ and pulse width of 9.9 ns. The ramp-fire technique is used to maintain single frequency operation and the cavity length is modulated by an intracavity RbTiOPO$_{4}$ (RTP) crystal. The frequency stability (rms) of the output pulse is 1.99 MHz over 1 min and the linewidth is 64 MHz.

We propose a design and numerical study of an optically blueshift and redshift switchable metamaterial (MM) absorber in the terahertz regime. The MM absorber comprises a periodic array of metallic split-ring resonators (SRRs) with semiconductor silicon embedded in the gaps of MM resonators. The absorptive frequencies of the MM can be shifted by applying an external pump power. The simulation results show that, for photoconductivity of silicon ranging between 1 S/m and 4000 S/m, the resonance peak of the absorption spectra shifts to higher frequencies, from 0.67 THz to 1.63 THz, with a resonance tuning range of 59%. As the conductivity of silicon increases, the resonance frequencies of the MM absorber are continuously tuned from 1.60 THz to 1.16 THz, a redshift tuning range of 28%. As the conductivity increases above 30000 S/m, the resonance frequencies tend to be stable while the absorption peak has a merely tiny variation. The optical-tuned absorber has potential applications as a terahertz modulator or switch.

A V-folded digital laser using a spatial light modulator (SLM) for intra-cavity loss shaping is exploited to generate Hermite–Gaussian modes with on-demand mode order. With a $\pi$/2 astigmatic mode converter, vortex beams carrying on-demand orbital angular momentum (OAM) with a tunable range from $-11\hbar$ to $12\hbar$ are obtained. The mode order of the HG mode, hence the OAM of the vortex beam, is digitally switched by changing the phase pattern imposed on the SLM without requiring any mechanic alignment of the cavity. This work has great potential applications in various OAM-tunable vortex beams.

Landau–Zener–Stückelberg (LZS) interference has drawn renewed attention to quantum information processing research because it is not only an effective tool for characterizing two-level quantum systems but also a powerful approach to manipulate quantum states. Superconducting quantum circuits, due to their versatile tunability and degrees of control, are ideal platforms for studying LZS interference phenomena. We use a superconducting Xmon qubit to study LZS interference by parametrically modulating the qubit transition frequency nonlinearly. For dc flux biasing of the qubit slightly far away from the optimal flux point, the qubit excited state population shows an interference pattern that is very similar to the standard LZS interference in linear regime, except that all bands shift towards lower frequencies when increasing the rf modulation amplitude. For dc flux biasing close to the optimal flux point, the negative sidebands and the positive sidebands behave differently, resulting in an asymmetric interference pattern. The experimental results are also in good agreement with our analytical and numerical simulations.

Optical operations have served as the basis of spectroscopy and imaging in terahertz regimes for a long time. Available lenses are practical tools for modulations. We fabricate a kind of biconvex lens from the natural dolomite cluster. The lens works well at 0.1 THz based on the relatively high refractive index and low absorption coefficients. Compared with the lens fabricated by a dolomite stone, such a lens can focus dispersive terahertz beam efficiently in terahertz imaging systems, which indicates that natural minerals hold promising applications in terahertz optics.

A femtosecond LBO optical parametric oscillator (OPO) with widely adjustable repetition rate by fractionally decrement of the cavity length is demonstrated. The repetition rate of 755 MHz to 1.43 GHz at an interval of 75.5 MHz is realized, which is 10 to 19 times that of the pump laser. The properties of output signal at 750 nm at different repetition rates are studied. The power of signal decreases with increasing the repetition rate. The maximum power of 194 mW at the repetition rate of 755 MHz and the minimum power of 22 mW at repetition rate of 1.43 GHz for the signal at 750 nm are obtained for the pump power of 3 W.

In recent years, orbital angular momentum (OAM), as a new usable degree of freedom of photons, has been widely applied in both classical optics and quantum optics. For example, digital spiral imaging uses the OAM spectrum of the output beam from the object to restore the symmetry information of the object. However, the related experiments have been carried out in free space so far. Due to the poor anti-noise performance, limited transmission distance and other reasons, the practicability is seriously restricted. Here, we have carried out a digital spiral imaging experiment through a few-mode fiber, to achieve the identification of the symmetry of object by measuring the OAM spectrum of the output beam. In experiment, we have demonstrated the identification of the symmetry of amplitude-only and phase-only objects with the two-, three- and four-fold rotational symmetries. We also give the understanding of the physics. We believe that our work has greatly improved the practical application of digital spiral imaging in remote sensing.

Using the linear local induction approximation, we investigate the self-induced motion of a vortex-line that corresponds to the motion of a particle in quantum mechanics. Provided Kelvin waves, the effective Schrödinger equation, physical quantity operators, and the corresponding path-integral formula can be obtained. In particular, the effective Planck constant defined by parameters of vortex-line motion shows the mathematical relation between the two fields. The vortexline–particle mapping may help in understanding particle motion in quantum mechanics.

An ultra-thin molybdenum(VI) oxide (MoO$_{3})$ modification layer can significantly improve hole injection from an electrode even though the MoO$_{3}$ layer does not contact the electrode. We find that as the thickness of the organic layer between MoO$_{3}$ and the electrode increases, the hole injection first increases and it then decreases. The optimum thickness of 5 nm corresponds to the best current improvement 70%, higher than that in the device where MoO$_{3}$ directly contacts the Al electrode. According to the 4,4-bis[N-(1-naphthyl)-N-phenyl-amino] biphenyl (NPB)/MoO$_{3}$ interface charge transfer mechanism and the present experimental results, we propose a mechanism that mobile carriers generated at the interface and accumulated inside the device change the distribution of electric field inside the device, resulting in an increase of the probability of hole tunneling through the injection barrier from the electrode, which also explains the phenomenon of hole injection enhanced by MoO$_{3}$/NPB/Al composite anode. Based on this mechanism, different organic materials other than NPB were applied to form the composite electrode with MoO$_{3}$. Similar current enhancement effects are also observed.

We study the transport property of single C$_{60}$ molecular transistors with special focus on the situation that other molecules are in vicinity. The devices are prepared using electromigration and thermal deposition techniques. Pure single C$_{60}$ molecule transistors show typical coulomb blockade behavior at low temperature. When we increase the coverage of molecules slightly by extending the deposition time, the transport spectrum of devices displays a switching behavior in the general coulomb blockade pattern. We attribute this unconventional phenomenon to the influence from a nearby C$_{60}$ molecule. By analyzing this transport behavior quantitatively based on the parallel-double-quantum-dot model, the interaction from the nearby molecule is proved to be of capacity and tunneling coupling. Thermal stimulation is also applied to the device to investigate the effect of local charging environment variation on intermolecular interaction.

We report a $^{19}\!$F nuclear magnetic resonance (NMR) study on single-crystal KCa$_{2}$Fe$_{4}$As$_{4}$F$_{2}$ ($T_{\rm c} \sim 33.3$ K). The $^{19}$F NMR spectral shape of KCa$_{2}$Fe$_{4}$As$_{4}$F$_{2}$ is weakly dependent on temperature and the Knight shift is small, which implies weak coupling between the CaF layer and the FeAs layer. The temperature dependence of 1/$^{19}\!T_{1}$ shows a hump below $T_{\rm c}$, however the 1/$^{75}\!T_{1}$ decreases just below $T_{\rm c}$, which implies that there are strong in-plane magnetic fluctuations in the CaF layers than in the FeAs layers. This may be caused by the motion of vortices. The absence of the coherence peak suggests unconventional superconductivity in KCa$_{2}$Fe$_{4}$As$_{4}$F$_{2}$.

We propose a diamond-based micron-scale sensor and perform high-resolution $B$-field imaging of the near-field distribution of coplanar waveguides. The sensor consists of diamond crystals attached to the tip of a tapered fiber with a physical size on the order of submicron. The amplitude of the $B$-field component $B$ is obtained by measuring the Rabi oscillation frequency. The result of Rabi sequence is fitted with a decayed sinusoidal. We apply the modulation-locking technique that demonstrates the vector-resolved field mapping of the micromachine coplanar waveguide structure (CPW). $B$-field line scan was performed on the CPW with a scan step size of 1.25 μm. To demonstrate vector resolved rf field sensing, a full field line scan acts (was performed) along four NV axes at a height of 50 μm above the device surface. The simulations are compared with the experimental results by vector-resolved measurement. This technique allows the measurement of weak microwave signals with a minimum resolvable modulation depth of 20 ppm. The sensor will have great interest in micron-scale resolved microwave $B$-field measurements, such as electromagnetic compatibility testing of microwave integrated circuits and characterization of integrated microwave components.