Generation of nonlinear vortex precursors

We numerically study the propagation of a few-cycle pulse carrying orbital angular momentum (OAM) through a dense atomic system. Nonlinear precursors consisting of high-order vortex har- monics are generated in the transmitted field due to ultrafast Bloch oscillation. The nonlinear precursors survive to propagation effects and are well separated with the main pulse, which provide a straightforward way of measuring precursors. By the virtue of carrying high-order OAM, the obtained vortex precursors as information carriers have potential applications in optical informa- tion and communication fields where controllable loss, large information-carrying capacity and high speed communication are required

The origin of the Redshift Spikes in the reflection spectrum of a Few-cycle Pulse in a Dense Medium

We give a detailed description about the reflected spectrum of a few-cycle pulse propagating through a resonant dense medium. An unexpected low-frequency spike appeared in the red edge of the spectrum. To figure out the origin of this redshift spike, we analysis the mechanisms responsible for the redshift of the reflected field. So far, the redshift has not been well studied for few-cycle pulses except a brief explanation made by the previous study [Kaloshan et al., Phys. Rev. Lett. 83 544 (1999).], which attributed the origin of the redshift to the so-called intrapulse four-wave mixing. However, we demonstrate numerically that the redshift consists of two separated spikes is actually produced by the Doppler effect of backpropagation waves, which is an analogue effect of dynamic nonlinear optical skin effect. Our study elucidates the underlying physics of the dynamic nonlinear optical effects responsible for the redshift spikes. Moreover, the dependency of the their frequency on the laser and medium parameters, such as medium density and input pulse area are also discussed

Squeezing effect induced by minimal length uncertainty

In this work, the dynamics of the deformed one-dimensional harmonic oscillator with minimal length uncertainty is examined and the analytical solutions for time evolution of position and momentum operators are presented in which the rough approximation that neglects the higher order terms in BakerHausdor lemma is avoided. Based on these analytical solutions the uncertainties for position and momentum operators are calculated in a coherent state, and an unexpected squeezing effect in both coordinate and momentum directions is found in comparison with ordinary harmonic oscillator. Obviously such a squeezing effect is induced by the minimal length uncertainty (gravitational effects). Our results are applied to the electrons trapped in strong magnetic fields to examine the degree of the existing squeezing effect in a real system, which shows the squeezing degree induced by minimal length uncertainty is very small.Comment: 9 pages, 3 figure

Probing quantum grav ity effects with ion trap

The existence of minimal length scale has motivated the proposal of generalized uncertainty principle, which provides a potential routine to probe quantum gravitational effects in low-energy quantum mechanics experiment. Hitherto, the tabletop experiment of testing deviations from ordinary quantum mechanics are mostly based on microscopic objects. However, the feasibility of these studies are challenged by the recent study of spacetime quantization for composite macroscopic body. In this paper, we propose a scheme to probe quantum gravity effects by revealing the deviations from predictions of Heisenberg uncertainty principle. Our scheme focus on manipulating the interaction sequences between external laser fields and a single trapped ion to seek evidence of spacetime quantization, therefore reduce the complicity induced by large bodies to some extent. The relevant study for microscopic particles is crucial considering the lack of satisfactory theories regarding basic properties for multi-particles in the framework of quantum gravity. Meanwhile, we are managed to set a new upper limit for deformation parameter

Deep joint rain and haze removal from single images

Rain removal from a single image is a challenge which has been studied for a long time. In this paper, a novel convolutional neural network based on wavelet and dark channel is proposed. On one hand, we think that rain streaks correspond to high frequency component of the image. Therefore, haar wavelet transform is a good choice to separate the rain streaks and background to some extent. More specifically, the LL subband of a rain image is more inclined to express the background information, while LH, HL, HH subband tend to represent the rain streaks and the edges. On the other hand, the accumulation of rain streaks from long distance makes the rain image look like haze veil. We extract dark channel of rain image as a feature map in network. By increasing this mapping between the dark channel of input and output images, we achieve haze removal in an indirect way. All of the parameters are optimized by back-propagation. Experiments on both synthetic and real- world datasets reveal that our method outperforms other state-of- the-art methods from a qualitative and quantitative perspective.Comment: 6 page

Long-range self-interacting dark matter in the Sun

We investigate the implications of the long-rang self-interaction on both the self-capture and the annihilation of the self-interacting dark matter (SIDM) trapped in the Sun. Our discussion is based on a specific SIDM model in which DM particles self-interact via a light scalar mediator, or Yukawa potential, in the context of quantum mechanics. Within this framework, we calculate the self-capture rate across a broad region of parameter space. While the self-capture rate can be obtained separately in the Born regime with perturbative method, and the classical limits with the Rutherford formula, our calculation covers the gap between in a non-perturbative fashion. Besides, the phenomelogy of both the Sommerfeld-enhanced s- and p-wave annihilation of the solar SIDM is also involved in our discussion. Moreover, by combining the analysis of the Super-Kamiokande (SK) data and the observed DM relic density, we constrain the nuclear capture rate of the DM particles in the presence of the dark Yukawa potential. The consequence of the long-range dark force on probing the solar SIDM turns out to be significant if the force-carrier is much lighter than the DM particle, and a quantitative analysis is provided.Comment: matches the published versio

Tunable Spin-Orbit Torques in Cu-Ta Binary Alloy Heterostructures

The spin Hall effect (SHE) is found to be strong in heavy transition metals (HM), such as Ta and W, in their amorphous and/or high resistivity form. In this work, we show that by employing a Cu-Ta binary alloy as buffer layer in an amorphous Cu$_{100-x}$Ta$_{x}$-based magnetic heterostructure with perpendicular magnetic anisotropy (PMA), the SHE-induced damping-like spin-orbit torque (DL-SOT) efficiency $|\xi_{DL}|$ can be linearly tuned by adjusting the buffer layer resistivity. Current-induced SOT switching can also be achieved in these Cu$_{100-x}$Ta$_{x}$-based magnetic heterostructures, and we find the switching behavior better explained by a SOT-assisted domain wall propagation picture. Through systematic studies on Cu$_{100-x}$Ta$_{x}$-based samples with various compositions, we determine the lower bound of spin Hall conductivity $|\sigma_{SH}|\approx2.02\times10^{4}[\hbar/2e]\Omega^{-1}\cdot\operatorname{m}^{-1}$ in the Ta-rich regime. Based on the idea of resistivity tuning, we further demonstrate that $|\xi_{DL}|$ can be enhanced from 0.087 for pure Ta to 0.152 by employing a resistive TaN buffer layer

Boundary layer structure in turbulent Rayleigh-B\'enard convection in a slim box

The logarithmic law of mean temperature profile has been observed in different regions in Rayleigh-B\'enard turbulence. However, how thermal plumes correlate to the log law of temperature and how the velocity profile changes with pressure gradient are not fully understood. Here, we performed three-dimensional simulations of Rayleigh-B\'enard turbulence in a slim-box without the front and back walls with aspect ratio, $L:D:H=1:1/6:1$, in the Rayleigh number $Ra=[1\times10^8, 1\times10^{10}]$ for Prandtl number $Pr=0.7$. The velocity profile is successfully quantified by a two-layer function of a stress length, $\ell_u^+\approx \ell_0^+(z^+)^{3/2}\left[1+\left({z^+}/{z_{sub}^+}\right)^4\right]^{1/4}$, as proposed by She et al. (She 2017), though neither a Prandtl-Blasius-Pohlhausen type nor the log-law is seen in the viscous boundary layer. In contrast, the temperature profile in the plume-ejecting region is logarithmic for all simulated cases, being attributed to the emission of thermal plumes. The coefficient of the temperature log-law, $A$ can be described by composition of the thermal stress length $\ell^*_{\theta}$ and the thicknesses of thermal boundary layer $z^*_{sub}$ and $z^*_{buf}$, i.e. $A\simeq z^*_{sub}/\left(\ell^*_{\theta 0}{z^*_{buf}}^{3/2}\right)$. The adverse pressure gradient responsible for turning the wind direction contributes to thermal plumes gathering at the ejecting region and thus the log-law of temperature profile. The Nusselt number scaling and local heat flux of the present simulations are consistent with previous results in confined cells. Therefore, the slim-box RBC is a preferable system for investigating in-box kinetic and thermal structures of turbulent convection with the large-scale circulation on a fixed plane.Comment: 16 pages, 37 figure

The overshoot and phenotypic equilibrium in characterizing cancer dynamics of reversible phenotypic plasticity

The paradigm of phenotypic plasticity indicates reversible relations of different cancer cell phenotypes, which extends the cellular hierarchy proposed by the classical cancer stem cell (CSC) theory. Since it is still question able if the phenotypic plasticity is a crucial improvement to the hierarchical model or just a minor extension to it, it is worthwhile to explore the dynamic behavior characterizing the reversible phenotypic plasticity. In this study we compare the hierarchical model and the reversible model in predicting the cell-state dynamics observed in biological experiments. Our results show that the hierarchical model shows significant disadvantages over the reversible model in describing both long-term stability (phenotypic equilibrium) and short-term transient dynamics (overshoot) of cancer cells. In a very specific case in which the total growth of population due to each cell type is identical, the hierarchical model predicts neither phenotypic equilibrium nor overshoot, whereas thereversible model succeeds in predicting both of them. Even though the performance of the hierarchical model can be improved by relaxing the specific assumption, its prediction to the phenotypic equilibrium strongly depends on a precondition that may be unrealistic in biological experiments, and it also fails to capture the overshoot of CSCs. By comparison, it is more likely for the reversible model to correctly describe the stability of the phenotypic mixture and various types of overshoot behavior.Comment: 24 pages, 6 figure

The current-induced spin-orbit torque and field-free switching from Mo-based magnetic heterostructures

Magnetic heterostructure Mo/CoFeB/MgO has strong perpendicular magnetic anisotropy and thermal stability. Through current-induced hysteresis loop shift measurements, we show that the dampinglike spin-orbit torque (SOT) efficiency of Mo/CoFeB/MgO heterostructure is $\xi_{DL}\approx -0.003\pm 0.001$ and fairly independent of the annealing temperature from 300$^\circ$C to 400$^\circ$C. Though $|\xi_{DL}|$ is small while compare to those from Ta or W-based heterostructures, reversible current-induced SOT switching of a thermally-stable Mo/CoFeB/MgO heterostruture can still be achieved. Furthermore, we observe field-free current-induced switching from a Mo/CoFeB/MgO structure with the Mo layer being wedge-deposited. Our results indicate that even for a weak spin-orbit interaction 4d transition metal such as Mo, it is still possible to generate sufficient spin current for conventional SOT switching and to realize field-free current-induced switching by structural engineering