arXiv subjects

Jun He

Publications and source records attributed to Jun He.

At least 217 records · Page 12Linked to original sources

arXiv2020

Possible molecular states from the $NΔ$ interaction

Recently, a hint for dibaryon $NΔ(D_{21})$ was observed at WASA-AT-COSY with a mass about $30\pm10$ MeV below the $NΔ$ threshold. It has a relatively small binding energy compared with the $d^*(2380)$ and a width close to the width of the $Δ$ baryon, which suggests that it may be a dibaryon in a molecular state picture. In this work, we study the possible $S$-wave molecular states from the $NΔ$ interaction within the quasipotential Bethe-Salpeter equation approach. The interaction is described by exchanging $π$, $ρ$, and $ω$ mesons. With reasonable parameters, a $D_{21}$ bound state can be produced from the interaction. The results also suggest that there may exist two more possible $D_{12}$ and $D_{22}$ states with smaller binding energies. The $π$ exchange is found to play the most important role to bind two baryons to form the molecular states. An experimental search for possible $NΔ(D_{12})$ and $NΔ(D_{22})$ states will be helpful for understanding the hint of the dibaryon $NΔ(D_{21})$.

nucl-th↗

arXiv2020

Two-way single-photon-level frequency conversion between 852nm and 1560nm for connecting cesium D2 line with the telecom C-band

A compact setup for two-way single-photon-level frequency conversion between 852 nm and 1560 nm has been implemented with the same periodically-poled magnesium-oxide-doped lithium niobate (PPMgO:LN) bulk crystals for connecting cesium D2 line (852 nm) to telecom C-band. By single-pass mixing a strong continuous-wave pump laser at 1878 nm and the single-photon-level periodical signal pulses in a 50-mm-long PPMgO:LN bulk crystal, the conversion efficiency of ~1.7% ( ~1.9%) for 852-nm to 1560-nm down-conversion (1560-nm to 852-nm up-conversion) have been achieved. We analyzed noise photons induced by the strong pump laser beam, including the spontaneous Raman scattering (SRS) and the spontaneous parametric down-conversion (SPDC) photons, and the photons generated in the cascaded nonlinear processes. The signal-to-noise ratio (SNR) has been improved remarkably by using the narrow-band filters and changing polarization of the noise photons in the difference frequency generation (DFG) process. With further improvement of the conversion efficiency by employing PPMgO:LN waveguide, instead of bulk crystal, our study may provide the basics for cyclic photon conversion in quantum network.

physics.atom-ph↗

arXiv2020

Hidden-bottom molecular states from $Σ^{()}_bB^{()}-Λ_bB^{(*)}$ interaction

In this work, we study possible hidden-bottom molecular pentaquarks $P_b$ from coupled-channel $Σ^{(*)}_bB^{(*)}-Λ_bB^{(*)}$ interaction in the quasipotential Bethe-Salpeter equation approach. In isodoublet sector with $I=1/2$, with the same reasonable parameters the interaction produces seven molecular states, a state near $ Σ_bB$ threshold with spin parity $J^P=1/2^-$, a state near $Σ^*_bB$ threshold with $3/2^-$, two states near $Σ_bB^*$ threshold with $1/2^-$ and $3/2^-$, and three states near $Σ_b^*B^*$ threshold with $1/2^-$, $3/2^-$, and $5/2^-$. The results suggest that three states near $Σ_b^* B^*$ threshold and two states near $Σ_b B^*$ threshold are very close, respectively, which may be difficult to distinguish in experiment without partial wave analysis. Compared with the hidden-charm pentaquark, the $P_b$ states are relatively narrow with widths at an order of magnitude of 1 MeV or smaller. The importance of each channel considered is also discussed, and it is found that the $Λ_b B^*$ channel provides important contribution for the widths of those states. In isoquartet sector with $I=3/2$, cutoff should be considerably enlarged to achieve bound states from the interaction, which makes the existence of such states unreliable. The results in the current work are helpful for searching for hidden-bottom molecular pentaquarks in future experiments, such as the COMPASS, J-PARC, and the Electron Ion Collider in China (EicC).

hep-ph↗

arXiv2020

Rydberg level shift due to the electric field generated by Rydberg atom collision induced ionization in cesium atomic ensemble

We experimentally studied the Rydberg level shift caused by the electric field, which is generated by Rydberg atom collision induced ionization in a cesium atomic ensemble. The density of charged particles caused by collisions between Rydberg atoms is changed by controlling the ground-state atomic density and optical excitation process. We measured the Rydberg level shift using Rydberg electromagnetically-induced-transparency (EIT) spectroscopy, and interpreted the physical origin using a semi-classical model. The experimental results are in good agreement with the numerical simulation. These energy shifts are important for the self-calibrated sensing of microwave field by the employing of Rydberg EIT. Moreover, in contrast to the resonant excitation case, narrow-linewidth spectroscopy with high signal-to-noise ratio would be useful for high-precision measurements.

physics.atom-ph↗

arXiv2020

Characterizing linear mappings through zero products or zero Jordan products

Let $\mathcal{A}$ be a $*$-algebra and $\mathcal{M}$ be a $*$-$\mathcal A$-bimodule, we study the local properties of $*$-derivations and $*$-Jordan derivations from $\mathcal{A}$ into $\mathcal{M}$ under the following orthogonality conditions on elements in $\mathcal A$: $ab^*=0$, $ab^*+b^*a=0$ and $ab^*=b^*a=0$. We characterize the mappings on zero product determined algebras and zero Jordan product determined algebras. Moreover, we give some applications on $C^*$-algebras, group algebra, matrix algebras, algebras of locally measurable operators and von Neumann algebras.

math.OA↗

arXiv2020

The $X(2239)$ and $η(2225)$ as hidden-strange molecular states from $Λ\barΛ$ interaction

In this work, we propose a possible assignment of the newly observed $X(2239)$, as well as the $η(2225)$, as a molecular state from the interaction of a baryon $Λ$ and an antibaryon $\barΛ$. With the help of effective Lagrangians, the $Λ\barΛ$ interaction is described within the one-boson-exchange model with $η$, $η'$, $ω$, $ϕ$, and $σ$ exchanges considered. After inserting the potential kernel into the quasipotential Bethe-Salpeter equation, the bound states from the $Λ\barΛ$ interaction can be studied by searching for the pole of the scattering amplitude. Two loosely bound states with spin parities $I^G(J^{PC})=0^+(0^{-+})$ and $0^-(1^{--})$ appear near the threshold almost with the same parameter. The $0^-(1^{--})$ state can be assigned to the $X(2239)$ observed at BESIII, which is very close to the $Λ\barΛ$ threshold. The scalar meson $η(2225)$ can be interpreted as a $0^+(0^{-+})$ state from the $Λ\barΛ$ interaction. The annihilation effect is also discussed through a coupled-channel calculation plus a phenomenological optical potential. It provides large widths to two bound states produced from the $Λ\barΛ$ interaction. The mass of the $1^-$ state is a little larger than the mass of the $0^-$ state after including the annihilation effect, which is consistent with our assignment of these two states as $X(2239)$ and $η(2225)$, respectively. The results suggest that further investigation is expected to understand the structures near the $Λ\barΛ$ threshold, such as $X(2239)$, $η(2225)$, and $X(2175)$.

hep-ph↗

arXiv2020

Stochastic switching in Rydberg atomic ensemble

We demonstrated stochastic switching in a bistable system implemented with Rydberg atomic ensemble. The transition between the two states of the bistable system is driven by intensity noise of the laser beams. Rydberg atomic ensemble accumulates energy in an equilibrium situation and brings the nonlinear system across the threshold, where stochastic switching occurs between the two states. Measurement of Rydberg state's population by means of the ladder-type electromagnetically-induced transparency approaching relevant Rydberg state allows us to investigate the nonlinear behavior in Rydberg atomic ensemble based bistable system experimentally.

physics.atom-ph↗

arXiv2020

Systematic study on production of hidden-bottom pentaquark via $γp$ and $π^{-}p$ scatterings

The production of hidden-bottom pentaquark $P_{b}$ states via $γp$ and $π^{-}p$ scatterings is studied within an effective Lagrangian approach and the vector-meson-dominance mechnism. For the $P_{b}$ production in the process $γp\rightarrow Υp$, the dipole Pomeron model is employed to calculate the background contribution, and the experimental data can be well described. For the process $π^{-}p\rightarrow Υn$, the Reggeized $t$-channel with $π$ exchange is considered as the main background for the $P_{b}$ production. Near the threshold, two-peak structure from the states $P_{b (11080)$ and $P_{b}(11125)$ can be observed if energy bin width is chosen as 0.01 GeV, and the same result is obtained in the $π^{-}p$ scattering. Moreover, by taking the branching ratio of Br$[{P_{b}\rightarrow πN}]\simeq 0.05\%$, the numerical result shows that the average value of cross section from the $P_{b}(11080)$ state produced in the $γp$ or $π^{-}p$ scattering reaches at least 0.1 nb with a bin of 0.1 GeV. Even if we reduce the branching ratio of the $P_{b}$ state into $πN$ channel by one order, the theoretical average of the cross section from $P_{b}(11080)$ production in $π^{-}p$ scattering can reach the order of 0.01 nb with a bin of 0.1 GeV, which means that the signal can still be clearly distinguished from the background. The experimental measurements and studies on the hidden-bottom pentaquark $P_{b}$ state production in the $γp $ or $π^{-}p$ scattering near-threshold energy region around $W\simeq 11$ GeV are strongly suggested, which are accessible at COMPASS and JPARC. Particularly, the result of the photoproduction suggests that it is very promising to observe the hidden-bottom pentaquark at proposed EicC facility in China.

hep-ph↗

arXiv2020

Y(4626) as a molecular state from interaction ${D}^*_s\bar{D}_{s1}(2536)-{D}_s\bar{D}_{s1}(2536)$

Recently, a new structure $Y(4626)$ was reported by the Belle Colloboration in the process $e^+e^-\to D_s^+D_{s1}(2536)^-$. In this work, we propose an assignment of the $Y(4626)$ as a ${D}^*_s\bar{D}_{s1}(2536)$ molecular state, which decays into the $D_s^+D_{s1}(2536)^-$ channel through a coupling between ${D}^*_s\bar{D}_{s1}(2536)$ and ${D}_s\bar{D}_{s1}(2536)$ channels. With the help of the heavy quark symmetry, the potential of the interaction ${D}^*_s\bar{D}_{s1}(2536)-{D}_s\bar{D}_{s1}(2536)$ is constructed within the one-boson-exchange model, and inserted into the quasipotential Bethe-Salpeter equation. The pole of obtained scattering amplitude is searched for in the complex plane, which corresponds to a molecular state from the interaction ${D}^*_s\bar{D}_{s1}(2536)-{D}_s\bar{D}_{s1}(2536)$. The results suggest that a pole is produced near the ${D}^*_s\bar{D}_{s1}(2536)$ threshold, which exhibits as a peak in the invariant mass spectrum of the ${D}_s\bar{D}_{s1}(2536)$ channel at about 4626 MeV. It obviously favors the $Y(4265)$ as a ${D}^*_s\bar{D}_{s1}(2536)$ molecular state. In the same model, other molecular states from the interaction ${D}^*_s\bar{D}_{s1}(2536)-{D}_s\bar{D}_{s1}(2536)$ are also predicted, which can be checked in future experiments.

hep-ph↗

arXiv2020

Topological-darkness-assisted phase regulation for atomically thin meta-optics

Two-dimensional (2D) noble-metal dichalcogenides have emerged as a new platform for the realization of versatile flat optics with a considerable degree of miniaturization. However, light field manipulation at the atomic scale is widely considered unattainable since the vanishing thickness and intrinsic losses of 2D materials completely suppress both resonances and phase accumulation effects. Empowered by conventionally perceived adverse effects of intrinsic losses, we show that the structured PtSe2 films integrated with a uniform substrate can regulate nontrivial singular phase and realize atomic-thick meta-optics in the presence of topological darkness. We experimentally demonstrate a series of atomic-thick binary meta-optics that allows angle-robust and high unit-thickness diffraction efficiency of 0.96%/nm in visible frequencies, given its thickness of merely 4.3 nm. Our results unlock the potential of a new class of 2D flat optics for light field manipulation at an atomic thickness.

physics.optics↗

arXiv2020

Real-time Human Activity Recognition Using Conditionally Parametrized Convolutions on Mobile and Wearable Devices

Recently, deep learning has represented an important research trend in human activity recognition (HAR). In particular, deep convolutional neural networks (CNNs) have achieved state-of-the-art performance on various HAR datasets. For deep learning, improvements in performance have to heavily rely on increasing model size or capacity to scale to larger and larger datasets, which inevitably leads to the increase of operations. A high number of operations in deep leaning increases computational cost and is not suitable for real-time HAR using mobile and wearable sensors. Though shallow learning techniques often are lightweight, they could not achieve good performance. Therefore, deep learning methods that can balance the trade-off between accuracy and computation cost is highly needed, which to our knowledge has seldom been researched. In this paper, we for the first time propose a computation efficient CNN using conditionally parametrized convolution for real-time HAR on mobile and wearable devices. We evaluate the proposed method on four public benchmark HAR datasets consisting of WISDM dataset, PAMAP2 dataset, UNIMIB-SHAR dataset, and OPPORTUNITY dataset, achieving state-of-the-art accuracy without compromising computation cost. Various ablation experiments are performed to show how such a network with large capacity is clearly preferable to baseline while requiring a similar amount of operations. The method can be used as a drop-in replacement for the existing deep HAR architectures and easily deployed onto mobile and wearable devices for real-time HAR applications.

cs.CV↗

arXiv2020

Towards implementation of a magic optical-dipole trap for confining ground-state and Rydberg-state cesium cold atoms

Long ground-Rydberg coherence lifetime is interesting for implementing high-fidelity quantum logic gates, many-body physics, and other quantum information protocols. However, the potential formed by a conventional far-off-resonance red-detuned optical-dipole trap (ODT) is usually repulsive for Rydberg atoms, which will result in fast atom loss and low repetition rate of the experimental sequence. These issues can be addressed by a magic ODT. We performed the calculation of ODT's magic detuning for confinement of cesium ground state and Rydberg state with the same potential well. We used a sum-over-states method to calculate the dynamic polarizabilities of $6S_{1/2}$ ground state and highly-excited ($nS_{1/2}$ and $nP_{3/2}$) Rydberg state of cesium atoms, and identify corresponding magic detuning for optical wavelengths in the range of $850 - 2000$ nm. We estimated the trapping lifetime of cesium Rydberg atoms confined in the magic ODT by including different dissipative mechanisms. Furthermore, we have experimentally realized an 1879.43-nm single-frequency laser system with a watt-level output power for setting up the magic ODT for $6S_{1/2}$ ground-state and $84P_{3/2}$ Rydberg-state cesium cold atoms.

physics.atom-ph↗

arXiv2020

Memory-Augmented Relation Network for Few-Shot Learning

Metric-based few-shot learning methods concentrate on learning transferable feature embedding that generalizes well from seen categories to unseen categories under the supervision of limited number of labelled instances. However, most of them treat each individual instance in the working context separately without considering its relationships with the others. In this work, we investigate a new metric-learning method, Memory-Augmented Relation Network (MRN), to explicitly exploit these relationships. In particular, for an instance, we choose the samples that are visually similar from the working context, and perform weighted information propagation to attentively aggregate helpful information from the chosen ones to enhance its representation. In MRN, we also formulate the distance metric as a learnable relation module which learns to compare for similarity measurement, and augment the working context with memory slots, both contributing to its generality. We empirically demonstrate that MRN yields significant improvement over its ancestor and achieves competitive or even better performance when compared with other few-shot learning approaches on the two major benchmark datasets, i.e. miniImagenet and tieredImagenet.

cs.CV↗

arXiv2020

Reconciling the X(2240) with the Y(2175)

In the present work, we reanalyzed the cross sections for $e^+ e^- \to K^+K^-$, where a new structure $X(2240)$ was reported by BES III Collaboration. By including the interference between the direct coupling and vector meson intermediate processes, we find the mass and width of $X(2240)$ are $2197.4\pm 4.4$ MeV and $75.6\pm 7.2 $ MeV, respectively, which are well consistent with the PDG average values of the resonance parameters for $Y(2175)$, thus, we conclude that the $X(2240)$ should be the same state as the $Y(2175)$.

hep-ph↗

arXiv2020

Helper and Equivalent Objectives: An Efficient Approach to Constrained Optimisation

Numerous multi-objective evolutionary algorithms have been designed for constrained optimisation over past two decades. The idea behind these algorithms is to transform constrained optimisation problems into multi-objective optimisation problems without any constraint, and then solve them. In this paper, we propose a new multi-objective method for constrained optimisation, which works by converting a constrained optimisation problem into a problem with helper and equivalent objectives. An equivalent objective means that its optimal solution set is the same as that to the constrained problem but a helper objective does not. Then this multi-objective optimisation problem is decomposed into a group of sub-problems using the weighted sum approach. Weights are dynamically adjusted so that each subproblem eventually tends to a problem with an equivalent objective. We theoretically analyse the computation time of the helper and equivalent objective method on a hard problem called ``wide gap''. In a ``wide gap'' problem, an algorithm needs exponential time to cross between two fitness levels (a wide gap). We prove that using helper and equivalent objectives can shorten the time of crossing the ``wide gap''. We conduct a case study for validating our method. An algorithm with helper and equivalent objectives is implemented. Experimental results show that its overall performance is ranked first when compared with other eight state-of-art evolutionary algorithms on IEEE CEC2017 benchmarks in constrained optimisation.

math.OC↗

arXiv2020

Influence of Laser Intensity Fluctuation on Single-Cesium Atom Trapping Lifetime in a 1064-nm Microscopic Optical Tweezer

An optical tweezer composed of a strongly focused single-spatial-mode Gaussian beam of a red-detuned 1064-nm laser can confine a single-cesium (Cs) atom at the strongest point of the light intensity. We can use this for coherent manipulation of single-quantum bits and single-photon sources. The trapping lifetime of the atoms in the optical tweezers is very short due to the impact of the background atoms, the laser intensity fluctuation of optical tweezer and the residual thermal motion of the atoms. In this paper, we analyzed the influence of the background pressure, the trap frequency of optical tweezers and the parametric heating of the optical tweezer on the atomic trapping lifetime. Combined with the external feedback loop based on an acousto-optical modulator (AOM), the intensity fluctuation of the 1064-nm laser in the time domain was suppressed from $\pm$ 3.360$\%$ to $\pm$ 0.064$\%$, and the suppression bandwidth reached approximately 33 kHz. The trapping lifetime of a single Cs atom in the microscopic optical tweezer was extended from 4.04 s to 6.34 s.

physics.atom-ph↗

arXiv2020

Laser Intensity Noise Suppression for Preparing Audio-Frequency 795 nm Squeezed Vacuum State of Light at Rubidium D1 Line

Laser intensity noise suppression has essential effects on preparation and characterization of the audio-frequency squeezed vacuum state of light based on a sub-threshold optical parametric oscillator (OPO).We have implemented two feedback loops by using relevant acousto-optical modulators (AOM) to stabilize the intensity of 795-nm near infrared (NIR) fundamental laser and 397.5-nm ultraviolet (UV) laser generated by cavity-enhanced frequency doubling.Typical peak-to-peak laser intensity fluctuation with a bandwidth of $\sim10$ kHz in a half hour has been improved from $\pm7.45$$\%$ to $\pm0.06$$\%$ for 795-nm NIR laser beam, and from $\pm9.04$$\%$ to $\pm0.05$$\%$ for 397.5-nm UV laser beam, respectively. The squeezing level of the squeezed vacuum state at 795 nm prepared by the sub-threshold OPO with a PPKTP crystal has been improved from -3.3 to -4.0 dB around 3$\sim$9 kHz of audio analysis frequency range.

physics.atom-ph↗

arXiv2020

Studying $X(2100)$ hadronic decays and predicting its pion and kaon induced productions

The newly observed $X(2100)$ by the BESIII Collaboration inspires our interest in studying the light meson system, especially axial-vector mesons. Since the $X(2100)$ has $J^P=1^+$ possibilities but cannot be distinguished only by mass, we make use of flux-tube model to study the strong decay behavior of $X(2100)$ under this assignment. The experimental width of the newly reported $X(2100)$ can be reproduced in our calculation, which favors an assignment of $X(2100)$ as the second radial excitation of $h_1(1380)$ with $I(J^P)=0(1^+)$. And the $\mathcal{B}(X(2100)\to ϕη^\prime)$ has a sizable contribution to the total width. Furthermore, we focus on the production of $X(2100)$ and its flavour partner $h_1(1965)$ induced by pion and kaon on a proton target with the Feynman model and the Regge model, which is an available platform to further identify their nature. The numerical results indicate that the total cross section are similar in the two models. When the range of momentum ${\mathrm{p_{Lab}}}$ is 10 to 30 GeV/$c$, the total cross sections for $π^-p\to X(2100)n$ and $K^-p\to X(2100)Λ$ are predicted to be at an order of magnitude of 0.1 $μ$b. Whereas, the total cross section for $π^-p\to h_1(1965)n$ is near an order of magnitude of 10 $μ$b when $p_{\mathrm{Lab}}$ is from 10 to 30 GeV/$c$, and much larger than that of reaction $K^-p\to h_1(1965)Λ$. These predictions can provide some valuable information to search for $X(2100)$ and $h_1(1965)$ in experiments at J-PARC, COMPASS, OKA@U-70 and SPS@CERN.

hep-ph↗