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X. H. Wang

Publications and source records attributed to X. H. Wang.

14 recordsLinked to original sources
arXiv2022

Neutron capture measurement and resonance parameter analysis of natSm

Multiple isotopes of samarium element are the isotopes produced by the s process, and 154Sm is produced by the r process. In addition, 144Sm is p nuclei in nuclear astrophysics. The measurement of these can help us to better understand the results of relevant photonuclear reaction experiments. On the other hand, 149Sm is a 235U fission product with a 1% yield, its cross sections are important to reactor neutronics. In this work, the neutron capture yield of the natural samarium target was measured at the back-streaming white neutron beamline (Back-n) of the China Spallation Neutron Source (CSNS), and the resonance parameters were analyzed by SAMMY code. The resonance peaks and the neutron separation energies contributed by the different isotopes are considered individually. The results of the capture yield found signs of the possibility of two resonance peaks at 8 eV, which awaits further experimental examination. Cross-section was calculated according to resonance parameters and was compared with other experimental results and evaluation databases of ENDF/B-VIII.0 and CENDL-3.2. A clear difference between ENDF/B VIII.0 and CENDL-3.2 database appears at 23.2 eV, the experimental result at this energy is smaller than data of ENDF/B VIII.0 database but CENDL-3.2 database. Most of the controversial experimental results invariably come from the samarium 149 isotope.

nucl-ex↗
arXiv2019

Photon statistics and dynamics of nanolasers subject to intensity feedback

Using a fully stochastic numerical scheme, we investigate the behaviour of a nanolaser in the low-coherence regime at the transition between spontaneous emission and lasing under the influence of intensity feedback. Studying the input-output curves as well as the second order correlations for different feedback fractions, we obtain an insight on the role played by the fraction of photons reinjected into the cavity. The interpretation of the observation is strengthened through the comparison with the temporal traces of the emitted photons and with the radiofrequency power spectra. The results give insight into the physics of nanolasers as well as validate the use of the second order autocorrelation as a sufficient tool for the interpretation of the dynamics. This confirmation offers a solid basis for the reliance on autocorrelations in experiments studying the effects of feedback in nanodevices.

physics.optics↗
arXiv2019

Controllable crystal restructuring in MXene by electron irradiation

Recent decades have witnessed the breakthroughs in utilizing electron beams as the smallest tools to tailor materials. Whereas, the manipulation of atoms in a controllable manner by the electron beams is a long-time challenge due to the random nature of atom-knock-on. Here, we show that electron irradiation can controllably manipulate atoms in newly-developed MXene multilayers. The multilayers consist of many few-atom-thick transition metal carbide slabs that are terminated with hydroxyl and O functional groups on each slab. Upon electron irradiation, the H atoms of the hydroxyl are knocked off, creating cation traps surrounded by dangling O confined in a nano-sized slit. Simultaneously, the transition metal atoms partially struck away from the carbide slabs migrate into the cation traps periodically, resulting in crystal restructuring. Crystal restructuring is versatile for various MXenes and dramatically improves the electric conductivity and lessens the anisotropy, holding significant implications in engineering MXenes at the atomic scale.

cond-mat.mtrl-sci↗
arXiv2018

Full-dimensional Quantum Dynamics of SiO in Collision with H$_2$

We report the first full-dimensional potential energy surface (PES) and quantum mechanical close-coupling calculations for scattering of SiO due to H$_2$. The full-dimensional interaction potential surface was computed using the explicitly correlated coupled-cluster (CCSD(T)-F12b) method and fitted using an invariant polynomial approach. Pure rotational quenching cross sections from initial states $v_1=0$, $j_1$=1-5 of SiO in collision with H$_2$ are calculated for collision energies between 1.0 and 5000 cm$^{-1}$. State-to-state rotational rate coefficients are calculated at temperatures between 5 and 1000 K. The rotational rate coefficients of SiO with para-H$_2$ are compared with previous approximate results which were obtained using SiO-He PESs or scaled from SiO-He rate coefficients. Rovibrational state-to-state and total quenching cross sections and rate coefficients for initially excited SiO($v_1=1, j_1$=0 and 1) in collisions with para-H$_2$($v_2=0,j_2=0$) and ortho-H$_2$($v_2=0,j_2=1$) were also obtained. The application of the current collisional rate coefficients to astrophysics is briefly discussed.

physics.chem-ph↗
arXiv2017

A data acquisition system based on ROOT and waveform digital technology for Photo-Neutron Source

The data acquisition system is based on ROOT and waveform digital technology, including neutron detector, waveform digitizer, PCI card, optical fiber, computer, reaction target device, stepper motor, data acquisition software and control target software. It achieves to acquire and record the waveform information of signal measured by the detector using a waveform digitizer. The specific target position is changed by the stepper motor which is remotely controlled by the data acquisition software and control target software. It is implemented by the exchange of information between the data acquisition software and the control target software. The system realizes to automatically open files and change targets at fixed intervals. It is capable of data compression by removing the data those are not signals, and automatic alarm when the beam is lost.

physics.ins-det↗
arXiv2011

Testing Bell inequalities with circuit QEDs by joint spectral measurements

We propose a feasible approach to test Bell's inequality with the experimentally-demonstrated circuit QED system, consisting of two well-separated superconducting charge qubits (SCQs) dispersively coupled to a common one-dimensional transmission line resonator (TLR). Our proposal is based on the joint spectral measurements of the two SCQs, i.e., their quantum states in the computational basis $\{|kl>,\,k,l=0,1\}$ can be measured by detecting the transmission spectra of the driven TLR: each peak marks one of the computational basis and its relative height corresponds to the probability superposed. With these joint spectral measurements, the generated Bell states of the two SCQs can be robustly confirmed without the standard tomographic technique. Furthermore, the statistical nonlocal-correlations between these two distant qubits can be directly read out by the joint spectral measurements, and consequently the Bell's inequality can be tested by sequentially measuring the relevant correlations related to the suitably-selected sets of the classical local variables $\{θ_j,θ_j', j=1,2\}$. The experimental challenges of our proposal are also analyzed.

quant-ph↗
arXiv2003

Canonical Form and Separability of PPT States in 2xMxN Composite Quantum Systems

We investigate the canonical forms of positive partial transposition (PPT) density matrices in ${\cal C}^2 \otimes {\cal C}^M \otimes {\cal C}^N$ composite quantum systems with rank $N$. A general expression for these PPT states are explicitly obtained. From this canonical form a sufficient separability condition is presented.

quant-ph↗
arXiv2003

Separability and entanglement in 2x3xN composite quantum systems

The separability and entanglement of quantum mixed states in $\Cb^2 \otimes \Cb^3 \otimes \Cb^N$ composite quantum systems are investigated. It is shown that all quantum states $ρ$ with positive partial transposes and rank $r(ρ)\leq N$ are separable.

quant-ph↗
arXiv2001

Linear response conductance and magneto-resistance of ferromagnetic single-electron transistors

The current through ferromagnetic single-electron transistors (SET's) is considered. Using path integrals the linear response conductance is formulated as a function of the tunnel conductance vs. quantum conductance and the temperature vs. Coulomb charging energy. The magneto-resistance of ferromagnet-normal metal-ferromagnet (F-N-F) SET's is almost independent of the Coulomb charging energy and is only reduced when the transport dwell time is longer than the spin-flip relaxation time. In all-ferromagnetic (F-F-F) SET's with negligible spin-flip relaxation time the magneto-resistance is calculated analytically at high temperatures and numerically at low temperatures. The F-F-F magneto-resistance is enhanced by higher order tunneling processes at low temperatures in the 'off' state when the induced charges vanishes. In contrast, in the 'on' state near resonance the magneto-resistance ratio is a non-monotonic function of the inverse temperature.

cond-mat.mes-hall↗
arXiv1999

Large Magnetoresistance Ratio in Ferromagnetic Single-Electron Transistors in the Strong Tunneling Regime

We study transport through a ferromagnetic single-electron transistor. The resistance is represented as a path integral, so that systems where the tunnel resistances are smaller than the quantum resistance can be investigated. Beyond the low order sequential tunneling and co-tunneling regimes, a large magnetoresistance ratio at sufficiently low temperatures is found. In the opposite limit, when the thermal energy is larger than the charging energy, the magnetoresistance ratio is only slightly enhanced.

cond-mat.mes-hall↗
arXiv1999

Circuit Effect On The Current-Voltage Characteristics Of Ultrasmall Tunnel Junctions

We have used the method of generating functional in imaginary time to derive the current-voltage characteristics of a tunnel junction with arbitrary tunneling conductance, connected in series with an external impedance and a voltage source. We have shown that via the renormalized charging energy and the renormalized environment conductance, our nonperturbative expressions of the total action can be mapped onto the corresponding perturbative formulas. This provides a straightforward way to go beyond the perturbation theory. For the impedance being a pure resistance, we have calculated the conductance for various voltages and temperatures, and the results agree very well with experiments.

cond-mat.mes-hall↗
arXiv1998

Population Inversion Induced by Resonant States in Semiconductors

We present a theoretical prediction of a new mechanism for carrier population inversion in semiconductors under an applied electric field. The mechanism is originated from a coherent capture-emission type inelastic scattering of resonant states. We support our theory with concrete calculations for shallow acceptor resonant states in strained p-Ge where a lasing in THz frequency region has been recently observed.

cond-mat.mtrl-sci↗
arXiv1997

Charging Ultrasmall Tunnel Junctions in Electromagnetic Environment

We have investigated the quantum admittance of an ultrasmall tunnel junction with arbitrary tunneling strength under an electromagnetic environment. Using the functional integral approach a close analytical expression of the quantum admittance is derived for a general electromagnetic environment. We then consider a specific controllable environment where a resistance is connected in series with the tunneling junction, for which we derived the dc quantum conductance from the zero frequency limit of the imaginary part of the quantum admittance. For such electromagnetic environment the dc conductance has been investigated in recent experiments, and our numerical results agree quantitatively very well with the measurements. Our complete numerical results for the entire range of junction conductance and electromagnetic environmental conductance confirmed the few existing theoretical conclusions.

cond-mat.mes-hall↗