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We report the production of $^{39}$K and $^{87}$Rb Bose-Einstein condensates (BECs) in the lowest hyperfine states $| F=1,m_{F}=1 \rangle$ simultaneously. We collect atoms in bright/dark magneto-optical traps (MOTs) of $^{39}$K/$^{87}$Rb to overcome the light-assisted losses of $^{39}$K atoms. Gray molasses cooling on the D1 line of the $^{39}$K is used to effectively increase the phase density, which improves the loading efficiency of $^{39}$K into the quadrupole magnetic trap. Simultaneously, the normal molasses are employed for $^{87}$Rb. After the microwave evaporation cooling on $^{87}$Rb in the optically plugged magnetic trap, the atoms mixture is transferred to a crossed optical dipole trap, where the collisional properties of the two species in different combinations of the hyperfine states are studied. The dual species BECs of $^{39}$K and $^{87}$Rb are obtained by further evaporative cooling in optical dipole trap at a magnetic field of 372.6 G with the background repulsive interspecies scattering length $a_{KRb}$ = 34 $a_{0}$ ($a_{0}$ is the Bohr radius) and the intraspecies scattering length $a_{K}$ = 20.05 $a_{0}$., Comment: 8 pages, 7 figures, Accepted by Chinese Phys. B

We show that it is possible to realize a cosmological bouncing solution in an anisotropic but homogeneous Bianchi-I background in a class of non-local, infinite derivative theories of gravity. We show that the anisotropic shear grows slower than in general relativity during the contraction phase, peaks to a finite value at the bounce point, and then decreases as the universe asymptotes towards isotropy and homogeneity, and ultimately to de Sitter. Along with a cosmological constant, the matter sector required to drive such a bounce is found to consist of three components - radiation, stiff matter and $k$-matter (whose energy density decays like the inverse square of the average scale factor). Generically, $k$-matter exerts anisotropic pressures. We will test the bouncing solution in local and non-local gravity and show that in the latter case it is possible to simultaneously satisfy positivity of energy density and, at least in the late time de Sitter phase, avoid the introduction of propagating ghost/tachyonic modes., Comment: 18 pages, 1 figure, 1 table. We dedicate this work to the memory of John D. Barrow. v2 matches the one published in JCAP

Recently, a distinct shadow mechanism was proposed by Wang et al. from the asymmetric thin-shell wormhole (ATW) in [Phys. Lett. B 811 (2020) 135930]. On the other hand, Gralla et al's work [Phys. Rev. D 100 (2019) 2, 024018] represented a nice description of photon rings in the presence of an accretion disk around a black hole. In this paper, we are inspired to thoroughly investigate the observational appearance of an accretion disk around the ATW. Although the spacetime outside an ATW with a throat could be identical to that containing a black hole with its event horizon, we show evident additional photon rings from the ATW spacetime. Moreover, a potential lensing band between two highly demagnified photon rings is found. Our analysis provides an optically observational signature to distinguish ATWs from black holes., Comment: 12 pages, 7 figures

Owing to the inevitable loss in communication channels, the distance of entanglement distribution is limited to approximately 100 kilometres on the ground. Quantum repeaters can circumvent this problem by using quantum memory and entanglement swapping. As the elementary link of a quantum repeater, the heralded distribution of two-party entanglement between two remote nodes has only been realized with built-in-type quantum memories. These schemes suffer from the trade-off between multiplexing capacity and deterministic properties and hence hinder the development of efficient quantum repeaters. Quantum repeaters based on absorptive quantum memories can overcome such limitations because they separate the quantum memories and the quantum light sources. Here we present an experimental demonstration of heralded entanglement between absorptive quantum memories. We build two nodes separated by 3.5 metres, each containing a polarization-entangled photon-pair source and a solid-state quantum memory with bandwidth up to 1 gigahertz. A joint Bell-state measurement in the middle station heralds the successful distribution of maximally entangled states between the two quantum memories with a fidelity of 80.4 $\pm$ 2.2 per cent ($\pm$1 standard deviation). The quantum nodes and channels demonstrated here can serve as an elementary link of a quantum repeater. Moreover, the wideband absorptive quantum memories used in the nodes are compatible with deterministic entanglement sources and can simultaneously support multiplexing, which paves the way for the construction of practical solid-state quantum repeaters and high-speed quantum networks., Comment: 36 pages, 11 figures

Erasure codes have been widely considered a promising solution to enhance data reliability at low storage costs. However, in modern geo-distributed storage systems, erasure codes may incur high data access latency as they require data retrieval from multiple remote storage nodes. This hinders the extensive application of erasure codes to data-intensive applications. This paper proposes novel caching schemes to achieve low latency in distributed coded storage systems. Experiments based on Amazon Simple Storage Service confirm the positive correlation between the latency and the physical distance of data retrieval. The average data access latency is used the performance metric to quantify the benefits of caching. Assuming that the future data popularity and network latency information is available, an offline caching scheme is proposed to find the optimal caching solution. Guided by the optimal scheme, an online caching scheme is proposed according to the measured data popularity and network latency information in real time. Experiment results demonstrate that the online scheme can approximate the optimal scheme well with dramatically reduced computation complexity., Comment: 12 pages, 13 figures, submitted to IEEE/ACM Transactions on Networking

The purpose of this paper is to enhance the conventional Komar integral to asymptotically anti-de Sitter (AdS) black holes. In order to do so, we first obtain a potential that is the linear combination of the usual Komar potential with two third-order derivative terms generated by the action of the d'Alembertian operator and the exterior derivative upon a Killing vector. Then this higher-order corrected potential is extended to the Einstein gravity with a negative cosmological constant, yielding the potential that is the linear combination of the usual Komar one with it acted on by the d'Alembertian. The surface integral of the improved Komar potential can serve as a formula for conserved charges of asymptotically AdS spacetimes. Finally, we make use of such a formula to compute the mass and the angular momentum of Schwarzschild-AdS black holes, regular AdS black holes, asymptotically AdS Kerr-Sen black holes, Kerr-NUT-AdS black holes, and Kerr-AdS black holes in arbitrary dimensions. The results coincide with the ones in the literature., Comment: 27 pages, No figures, minor revision to V1

We calculate the photon sphere $r_{ph}$ and critical curve $b_c$ for the quantum corrected Schwarzschild black hole, finding that they violate an universal inequalities proved for asymptotically flat black holes which satisfy null energy condition in the framework of Einstein gravity. This violation seem to be a common phenomenon when considering quantum modification of Einstein gravity. Furthermore, we study the shadows, lensing rings and photon rings in the quantum corrected Schwarzschild black hole. The violation leads to a larger bright lensing ring in the observational appearance of thin disk emission near the black hole compared with the classical Schwarzschild black hole. Our analysis may provide a observational evidence for quantum effect of general relativity., Comment: LaTex, 13 pages, 3 figures, 1 table

In the rapid cycling synchrotron of the China Spallation Neutron Source, the anti-correlated painting was adopted for the design scheme of the injection system. In the beam commissioning, with the optimization of the anti-correlated painting,the injection beam loss has been well controlled and the injection efficiency has exceeded 99%. Combined with other aspects of adjustments, the beam power on the target has reached 50 kW smoothly. In this paper, we have studied the injection optimization in the beam commissioning. Compared to the simulation results of the design scheme, the transverse beam distribution, transverse coupling effect and beam loss of the anti-correlated painting in the beam commissioning are somewhat different. Through the machine studies, we have carefully analyzed these differences and studied their reasons., Comment: 21 pages, 18 figures, submitted to Nucl. Instrum. Methods Phys. Res. A

In this paper, we study a class of higher derivative, non-local gravity which admits homogeneous and isotropic non-singular, bouncing universes in the absence of matter. At the linearized level, the theory propagates only a scalar degree of freedom, and no vector or tensor modes. The scalar can be made free from perturbative ghost instabilities, and has oscillatory and bounded evolution across the bounce., Comment: 5 pages, 1 figure