Catálogo de publicaciones - revistas

<jats:p>Phase-change material (PCM) is generating widespread interest as a new candidate for artificial synapses in bio-inspired computer systems. However, the amorphization process of PCM devices tends to be abrupt, unlike continuous synaptic depression. The relatively large power consumption and poor analog behavior of PCM devices greatly limit their applications. Here, we fabricate a GeTe/Sb<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub> superlattice-like PCM device which allows a progressive RESET process. Our devices feature low-power consumption operation and potential high-density integration, which can effectively simulate biological synaptic characteristics. The programming energy can be further reduced by properly selecting the resistance range and operating method. The fabricated devices are implemented in both artificial neural networks (ANN) and convolutional neural network (CNN) simulations, demonstrating high accuracy in brain-like pattern recognition.</jats:p>

<jats:p>Electron affinities (EA) of most lanthanide elements still remain unknown owing to their relatively lower EA values and the fairly complicated electronic structures. In the present work, we report the high-resolution photoelectron spectra of atomic cerium anion Ce<jats:sup>−</jats:sup> using the slow electron velocity-map imaging method in combination with a cold ion trap. The electron affinity of Ce is determined to be 4840.62(21) cm<jats:sup>−1</jats:sup> or 0.600160(26) eV. Moreover, several excited states of Ce<jats:sup>−</jats:sup> (<jats:sup>4</jats:sup>H<jats:sub>9/2</jats:sub>, <jats:sup>4</jats:sup>I<jats:sub>9/2</jats:sub>, <jats:sup>2</jats:sup>H<jats:sub>9/2</jats:sub>, <jats:sup>2</jats:sup>G<jats:sub>9/2</jats:sub>, <jats:sup>2</jats:sup>G<jats:sub>7/2</jats:sub>, <jats:sup>4</jats:sup>H<jats:sub>13/2</jats:sub>, <jats:sup>2</jats:sup>F<jats:sub>5/2</jats:sub>, and <jats:sup>4</jats:sup>I<jats:sub>13/2</jats:sub>) are observed.</jats:p>

<jats:p>We theoretically study the reversible process of quantum entanglement state by means of weak measurement and corresponding reversible operation. We present a protocol of the reversion operation in two bodies based on the theory of reversion of single photon and then expend it in quantum communication channels. The theoretical results demonstrate that the protocol does not break the information transmission after a weak measurement and a reversible measurement with the subsequent process in the transmission path. It can reverse the perturbed entanglement intensity evolution to its original state. Under the condition of different weak measurement intensity the protocol can reverse the perturbed quantum entanglement system perfectly. In the process we can get the classical information described by information gain from the quantum system through weak measurement operation. On the other hand, in order to realize complete reversibility, the classical information of the quantum entanglement system must obey a limited range we present in this paper in the reverse process.</jats:p>

<jats:p>We theoretically study the optical nonreciprocity in a piezo-optomechanical microdisk resonator, in which the cavity modes and the mechanical mode are optically pumped and piezoelectrically driven, respectively. For asymmetric optical pumping and different piezoelectrical drivings, our system shows some nonreciprocal optical responses. We find that our system can function as an optical isolator, a nonreciprocal amplifier, or a nonreciprocal phase shifter.</jats:p>

<jats:p>We theoretically investigate the frequency-nondegenerate and frequency degenerate squeezed lights with a four-wave mixing process (4WM) driven by two pump fields crossing at a small angle. Different from a 4WM process driven by a single pump field, the refractive index of the corresponding probe field, <jats:italic>n</jats:italic> <jats:sub>p</jats:sub>, can be converted to a value that is greater than 1 or less than 1 by an angle adjustment. In the new region with <jats:italic>n</jats:italic> <jats:sub>p</jats:sub> &lt; 1, the bandwidth of the gain is relatively large due to the slow change in the refractive index with the two-photon detuning. In this region with an exchange of the roles of the pump and probe beams, the frequency degenerate and spatial nondegenerate twin beams can be generated, which has potential application in quantum information and quantum metrology.</jats:p>

<jats:p>We develop a high-performance ultraviolet (UV) frequency stabilization technique implemented directly on UV diode lasers by combining the dichroic atomic vapor laser lock and the resonant transfer cavity lock. As an example, we demonstrate a stable locking with measured frequency standard deviations of approximately 200 kHz and 300 kHz for 399 nm and 370 nm diode lasers in 20 min. We achieve a long-term frequency drift of no more than 1 MHz for the target 370 nm laser within an hour, which is further verified with fluorescence count rates of a single trapped <jats:sup>171</jats:sup>Yb<jats:sup>+</jats:sup> ion. We also find strong linear correlations between lock points and environmental factors such as temperature and atmospheric pressure. Our approach provides a simple and stable solution at a relatively low cost, and features flexible control, high feedback bandwidth and minimal power consumption of the target UV laser.</jats:p>

<jats:p>In this review we discuss the recent progress in the simulation of soft active matter systems and in particular the hydrodynamics of microswimmers using the method of multiparticle collision dynamics, which solves the hydrodynamic flows around active objects on a coarse-grained level. We first present a brief overview of the basic simulation method and the coupling between microswimmers and fluid. We then review the current achievements in simulating flexible and rigid microswimmers using multiparticle collision dynamics, and briefly conclude and discuss possible future directions.</jats:p>

<jats:p>We present the variations of electrical parameters of dielectric barrier discharge (DBD) when the DBD generator is used for the material modification, whereas the relevant physical mechanism is also elaborated. An equivalent circuit model is applied for a DBD generator working in a filament discharging mode, considering the addition of epoxy resin (EP) as the plasma modified material. The electrical parameters are calculated through the circuit model. The surface conductivity, surface potential decay, trap distributions and surface charge distributions on the EP surface before and after plasma treatments were measured and calculated. It is found that the coverage area of micro-discharge channels on the EP surface is increased with the discharging time under the same applied AC voltage. The results indicate that the plasma modified material could influence the ignition of new filaments in return during the modification process. Moreover, the surface conductivity and density of shallow traps with low trap energy of the EP samples increase after the plasma treatment. The surface charge distributions indicate that the improved surface properties accelerate the movement and redistribution of charge carriers on the EP surface. The variable electrical parameters of discharge are attributed to the redistribution of deposited surface charge on the plasma modified EP sample surface.</jats:p>

<jats:p>Quantum gas microscopy has enabled the study on intriguing properties of ultracold atoms in optical lattices. It provides the cutting-edge technology for manipulating quantum many-body systems. In such experiments, atoms have to be prepared into a two-dimensional (2D) system for being resolved by microscopes with limited depth of focus. Here we report an experiment on slicing a single layer of the atoms trapped in a few layers of pancake-shaped optical traps to create a 2D system. This technique is implemented with a microwave “knife”, i.e., a microwave field with a frequency defined by the resonant condition with the Zeeman-shifted atomic levels related to a gradient magnetic field. It is crucial to keep a stable preparation of the desired layer to create the 2D quantum gas for future experimental applications. To achieve this, the most important point is to provide a gradient magnetic field with low noises and slow drift in combination with a properly optimized microwave pulse. Monitoring the electric current source and the environmental magnetic field, we applied an actively stabilizing circuit and realized a field drift of 0.042(3) mG/hour. This guarantees creating the single layer of atoms with an efficiency of 99.92(3)% while atoms are hardly seen in other layers within 48 hours, satisfying future experimental demands on studying quantum many-body physics.</jats:p>

<jats:p>A comparison of the nitrogen sources (N<jats:sub>2</jats:sub> and NH<jats:sub>3</jats:sub>) influence on AlN films grown by high-temperature halide vapor phase epitaxy (HVPE) is reported. The x-ray rocking curves (XRCs) indicate that the full width at half maximum (FWHM) of (0002) plane for AlN films using N<jats:sub>2</jats:sub> as nitrogen source is generally smaller than that using NH<jats:sub>3</jats:sub>. Optical microscope and atomic force microscope (AFM) results show that it is presently still more difficult to control the crack and surface morphology of AlN films with thicknesses of 5-10 μm using N<jats:sub>2</jats:sub> as the nitrogen source compared to that using NH<jats:sub>3</jats:sub>. Compared with one-step growth, two-step growth strategy has been proved more effective in stress control and reducing the density of threading dislocations for AlN epilayers using N<jats:sub>2</jats:sub> as the nitrogen source. These investigations reveal that using N<jats:sub>2</jats:sub> as nitrogen source in HVPE growth of AlN is immature at present, but exhibits great potential.</jats:p>