Showing papers in "Science China-physics Mechanics & Astronomy in 2018"

Three-step three-party quantum secure direct communication

Abstract: We propose a three-party quantum secure direct communication (QSDC) protocol with hyperentanglement in both spatial-mode and polarization degrees of freedom The secret message can be encoded independently with desired unitary operations in two degrees of freedom In this protocol, a party can synchronously obtain the other two parties messages Compared with previous three-party QSDC protocols, our protocol has several advantages First, the single photons in our protocol are only required to transmit for three times This advantage makes this protocol simple and useful Second, Alice and Bob can send different secret messages to Charlie, respectively Finally, with hyperentanglement, this protocol has a higher information capacity than other protocols

Insight -HXMT observations of the first binary neutron star merger GW170817

Abstract: Finding the electromagnetic (EM) counterpart of binary compact star merger, especially the binary neutron star (BNS) merger, is critically important for gravitational wave (GW) astronomy, cosmology and fundamental physics. On Aug. 17, 2017, Advanced LIGO and Fermi /GBM independently triggered the first BNS merger, GW170817, and its high energy EM counterpart, GRB 170817A, respectively, resulting in a global observation campaign covering gamma-ray, X-ray, UV, optical, IR, radio as well as neutrinos. The High Energy X-ray telescope (HE) onboard Insight -HXMT (Hard X-ray Modulation Telescope) is the unique high-energy gamma-ray telescope that monitored the entire GW localization area and especially the optical counterpart (SSS17a/AT2017gfo) with very large collection area (~1000 cm2) and microsecond time resolution in 0.2-5 MeV. In addition, Insight -HXMT quickly implemented a Target of Opportunity (ToO) observation to scan the GW localization area for potential X-ray emission from the GW source. Although Insight -HXMT did not detect any significant high energy (0.2-5 MeV) radiation from GW170817, its observation helped to confirm the unexpected weak and soft nature of GRB 170817A. Meanwhile, Insight -HXMT/HE provides one of the most stringent constraints (~10‒7 to 10‒6 erg/cm2/s) for both GRB170817A and any other possible precursor or extended emissions in 0.2-5 MeV, which help us to better understand the properties of EM radiation from this BNS merger. Therefore the observation of Insight -HXMT constitutes an important chapter in the full context of multi-wavelength and multi-messenger observation of this historical GW event.

Chemical vapor deposition growth of two-dimensional heterojunctions

Abstract: The properties of two-dimensional (2D) layered materials with atom-smooth surface and special interlayer van der Waals coupling are different from those of traditional materials. Due to the absence of dangling bonds from the clean surface of 2D layered materials, the lattice mismatch influences slightly on the growth of 2D heterojunctions, thus providing a flexible design strategy. 2D heterojunctions have attracted extensive attention because of their excellent performance in optoelectronics, spintronics, and valleytronics. The transfer method was utilized for the fabrication of 2D heterojunctions during the early stage of fundamental research on these materials. This method, however, has limited practical applications. Therefore, chemical vapor deposition (CVD) method was recently developed and applied for the preparation of 2D heterojunctions. The CVD method is a naturally down-top growth strategy that yields 2D heterojunctions with sharp interfaces. Moreover, this method effectively reduces the introduction of contaminants to the fabricated heterojunctions. Nevertheless, the CVD-growth method is sensitive to variations in growth conditions. In this review article, we attempt to provide a comprehensive overview of the influence of growth conditions on the fabrication of 2D heterojunctions through the direct CVD method. We believe that elucidating the effects of growth conditions on the CVD method is necessary to help control and improve the efficiency of the large-scale fabrication of 2D heterojunctions for future applications in integrated circuits.

Fast holonomic quantum computation based on solid-state spins with all-optical control

Abstract: Holonomic quantum computation is a quantum computation strategy that promises some built-in noise-resilience features. Here, we propose a scheme for nonadiabatic holonomic quantum computation with nitrogen-vacancy center electron spins, which are characterized by fast quantum gates and long qubit coherence times. By varying the detuning, amplitudes, and phase difference of lasers applied to a nitrogen-vacancy center, one can directly realize an arbitrary single-qubit holonomic gate on the spin. Meanwhile, with the help of cavity-assisted interactions, a nontrivial two-qubit holonomic quantum gate can also be induced. The distinct merit of this scheme is that all the quantum gates are obtained via an all-optical geometric manipulation of the solid-state spins. Therefore, our scheme opens the possibility for robust quantum computation using solid-state spins in an all-optical way.

Dark Matter Particle Explorer observations of high-energy cosmic ray electrons plus positrons and their physical implications

Abstract: The DArk Matter Particle Explorer (DAMPE) is a satellite-borne, high-energy particle and -ray detector, which is dedicated to indirectly detecting particle dark matter and studying high-energy astrophysics. The first results about precise measurement of the cosmic ray electron plus positron spectrum between 25 GeV and 4.6 TeV were published recently. The DAMPE spectrum reveals an interesting spectral softening arount 0:9 TeV and a tentative peak around 1:4 TeV. These results have inspired extensive discussion. The detector of DAMPE, the data analysis, and the first results are introduced. In particular, the physical interpretations of the DAMPE data are reviewed.

Detecting the neutrinos mass hierarchy from cosmological data

Abstract: We propose a new parameterization to measure the neutrino mass hierarchy, namely $\Delta=(m_3-m_1)/(m_1+m_3)$ which is dimensionless and varies in the range $[-1,1]$. Taking into account the results of neutrino oscillation experiments, $\Delta$ is the unique parameter for determining all the masses of neutrinos, and a positive (negative) sign of $\Delta$ denotes the normal (inverted) mass hierarchy. Adopting the currently available cosmic observations, we find that the normal mass hierarchy is slightly favored, and the mass of lightest neutrino is less than $0.030$ eV for the normal mass hierarchy and $0.024$ eV for the inverted mass hierarchy at $95\%$ confidence level.

Searching for sterile neutrinos in dynamical dark energy cosmologies

Abstract: We investigate how the dark energy properties change the cosmological limits on sterile neutrino parameters by using recent cosmological observations. We consider the simplest dynamical dark energy models, the wCDM model and the holographic dark energy (HDE) model, to make an analysis. The cosmological observations used in this work include the Planck 2015 CMB temperature and polarization data, the baryon acoustic oscillation data, the type Ia supernova data, the Hubble constant direct measurement data, and the Planck CMB lensing data. We find that, mv,terileff < 0.2675 eV and Ne f f < 3.5718 for ACDM cosmology, mv,terileff < 0.5313 eV and Ne f f < 3.5008 for wCDM cosmology, and raffterile < 0.1989 eV and Ne f f < 3.6701 for HDE cosmology, from the constraints of the combination of these data. Thus, without the addition of measurements of growth of structure, only upper limits on both mv,terileff and Ne f f can be derived, indicating that no evidence of the existence of a sterile neutrino species with eV-scale mass is found in this analysis. Moreover, compared to the ACDM model, in the wCDM model the limit on mv,terileff becomes much looser, but in the HDE model the limit becomes much tighter. Therefore, the dark energy properties could significantly influence the constraint limits of sterile neutrino parameters.

Probing the sign-changeable interaction between dark energy and dark matter with current observations

Abstract: We consider the models of vacuum energy interacting with cold dark matter in this study, in which the coupling can change sigh during the cosmological evolution. We parameterize the running coupling b by the form b(a) = b0a+be(1−a), where at the early-time the coupling is given by a constant be and today the coupling is described by another constant b0. We explore six specific models with (i) Q = b(a)H0ρ0, (ii) Q = b(a)H0ρde, (iii) Q = b(a)H0ρc, (iv) Q = b(a)Hρ0, (v) Q = b(a)Hρde, and (vi) Q = b(a)Hρc. The current observational data sets we use to constrain the models include the JLA compilation of type Ia supernova data, the Planck 2015 distance priors data of cosmic microwave background observation, the baryon acoustic oscillations measurements, and the Hubble constant direct measurement. We find that, for all the models, we have b0 0 at around the 1σ level, and b0 and be are in extremely strong anti-correlation. Our results show that the coupling changes sign during the evolution at about the 1σ level, i.e., the energy transfer is from dark matter to dark energy when dark matter dominates the universe and the energy transfer is from dark energy to dark matter when dark energy dominates the universe.

Realistic interpretation of quantum mechanics and encounter-delayed-choice experiment

Abstract: In this paper, a realistic interpretation (REIN) of the wave function in quantum mechanics is briefly presented.We demonstrate that in the REIN, the wave function of a microscopic object is its real existence rather than a mere mathematical description.Specifically, the quantum object can exist in disjointed regions of space just as the wave function is distributed, travels at a finite speed, and collapses instantly upon a measurement. Furthermore, we analyze the single-photon interference in a Mach-Zehnder interferometer (MZI) using the REIN. Based on this, we propose and experimentally implement a generalized delayed-choice experiment, called the encounter-delayed-choice experiment, where the second beam splitter is decided whether or not to insert at the encounter of two sub-waves along the arms of the MZI. In such an experiment, the parts of the sub-waves, which do not travel through the beam splitter, show a particle nature, whereas the remaining parts interfere and thus show a wave nature. The predicted phenomenon is clearly demonstrated in the experiment, thus supporting the REIN idea.

A brief review on μSR studies of unconventional Fe- and Cr-based superconductors

Abstract: Muon spin relaxation/rotation (μSR) is a vital technique for probing the superconducting gap structure, pairing symmetry and time reversal symmetry breaking, enabling an understanding of the mechanisms behind the unconventional superconductivity of cuprates and Fe-based high-temperature superconductors, which remain a puzzle. Very recently double layered Fe-based super- conductors having quasi-2D crystal structures and Cr-based superconductors with a quasi-1D structure have drawn considerable attention. Here we present a brief review of the characteristics of a few selected Fe- and Cr-based superconducting materials and highlight some of the major outstanding problems, with an emphasis on the superconducting pairing symmetries of these materials. We focus on μSR studies of the newly discovered superconductors ACa2Fe4As4F2 (A = K, Rb, and Cs), ThFeAsN, and A2Cr3As3 (A = K, Cs), which were used to determine the superconducting gap structures, the presence of spin fluctuations, and to search for time reversal symmetry breaking in the superconducting states. We also briefly discuss the results of μSR investigations of the superconductivity in hole and electron doped BaFe2As2.

Periodically poled lithium niobate whispering gallery mode microcavities on a chip

Abstract: In this study, we investigate the fabrication of periodically poled lithium niobate (PPLN) microdisk cavities on a chip. These resonators are fabricated from a PPLN film with a 16 μm poling period on insulator using conventional microfabrication techniques. The quality factor of the PPLN microdisk resonators with a 40-μm radius and a 700-nm thickness is 6.7×105. Second harmonic generation (SHG) with an efficiency of 2.2×10−6 mW−1 is demonstrated in the fabricated PPLN microdisks. The nonlinear conversion efficiency could be considerably enhanced by optimizing the period and pattern of the poled structure and by improving the cavity quality factors.

Simulating a topological transition in a superconducting phase qubit by fast adiabatic trajectories

Abstract: The significance of topological phases has been widely recognized in thecommunity of condensed matter physics. The well controllable quantum systemsprovide an artificial platform to probe and engineer various topologicalphases. The adiabatic trajectory of a quantum state describes thechange of the bulk Bloch eigenstates with the momentum, and this adiabatic simulation method is however practicallylimited due to quantum dissipation. Here we apply the “shortcut to adiabaticity” (STA)protocol to realize fast adiabatic evolutions in the system of a superconducting phase qubit.The resulting fast adiabatic trajectories illustratethe change of the bulk Bloch eigenstates in the Su-Schrieffer-Heeger (SSH) model. A sharp transitionis experimentally determined for the topological invariant of a winding number.Our experiment helps identify the topological Chern number of a two-dimensionaltoy model, suggesting the applicability of the fast adiabatic simulationmethod for topological systems.

Efficient universal quantum channel simulation in IBM’s cloud quantum computer

Abstract: The study of quantum channels is an important field and promises a wide range of applications, because any physical process can be represented as a quantum channel that transforms an initial state into a final state. Inspired by the method of performing non-unitary operators by the linear combination of unitary operations, we proposed a quantum algorithm for the simulation of the universal single-qubit channel, described by a convex combination of “quasi-extreme” channels corresponding to four Kraus operators, and is scalable to arbitrary higher dimension. We demonstrated the whole algorithm experimentally using the universal IBM cloud-based quantum computer and studied the properties of different qubit quantum channels. We illustrated the quantum capacity of the general qubit quantum channels, which quantifies the amount of quantum information that can be protected. The behavior of quantum capacity in different channels revealed which types of noise processes can support information transmission, and which types are too destructive to protect information. There was a general agreement between the theoretical predictions and the experiments, which strongly supports our method. By realizing the arbitrary qubit channel, this work provides a universally- accepted way to explore various properties of quantum channels and novel prospect for quantum communication.

Supernovae Ia in 2017: a long time delay from merger/accretion to explosion

Abstract: I use recent observational and theoretical studies of type Ia supernovae (SNe Ia) to further constrain the viable SN Ia scenarios and to argue that there must be a substantial time delay between the end of the merger of the white dwarf (WD) with a companion or the end of mass accretion on to the WD and its terminal explosion.This merger/accretion to explosion delay (MED) is required to allow the binary system to lead to a more or less spherical explosion and to prevent a pre-explosion ionizing radiation. Considering these recent results and the required MED, I conclude that the core degenerate scenario is somewhat more favorable over the other scenarios, followed by the double degenerate scenario. Although the single degenerate scenario is viable as well, it is less likely to account for common (normal) SN Ia. As all scenarios require substantial MED, the MED has turned from a disadvantage of the core degenerate scenario to a challenge that theory should overcome. I hope that the requirement for a MED will stimulate the discussion of the different SN Ia scenarios and the comparison of the scenarios to each other.

Micro- and nano-mechanics in China: A brief review of recent progress and perspectives

Abstract: The past three decades have witnessed the explosion of nanoscience and technology, where notable research efforts have been made in synthesizing nanomaterials and controlling nanostructures of bulk materials. The uncovered mechanical behaviors of structures and materials with reduced sizes and dimensions pose open questions to the community of mechanicians, which expand the framework of continuum mechanics by advancing the theory, as well as modeling and experimental tools. Researchers in China have been actively involved into this exciting area, making remarkable contributions to the understanding of nanoscale mechanical processes, the development of multi-scale, multi-field modeling and experimental techniques to resolve the processing-microstructures-properties relationship of materials, and the interdisciplinary studies that broaden the subjects of mechanics. This article reviews selected progress made by this community, with the aim to clarify the key concepts, methods and applications of micro- and nano-mechanics, and to outline the perspectives in this fast-evolving field.

The observational constraint on constant-roll inflation

Abstract: We discuss the constant-roll inflation with constant $\epsilon_2$ and constant $\bar\eta$.By using the method of Bessel function approximation, the analytical expressions for the scalar and tensor power spectra, the scalar and tensor spectral tilts,and the tensor to scalar ratio are derived up to the first order of $\epsilon_1$.The model with constant $\epsilon_2$ is ruled out by the observations at the $3\sigma$ confidence level, andthe model with constant $\bar\eta$ is consistent with the observations at the $1\sigma$ confidence level.The potential for the model with constant $\bar\eta$ is also obtained from the Hamilton-Jacobi equation.Although the observations constrain the constant-roll inflation to be the slow-roll inflation,the $n_\text{s}$-$r$ results from the constant-roll inflation are not the same as those from the slow-roll inflation even when $\bar\eta\sim~0.01$.

Lepton-portal dark matter in hidden valley model and the DAMPE recent results

Abstract: We study the recent $e^\pm$ cosmic ray excess reported by DAMPE in a Hidden Valley Model with lepton-portal dark matter. We find the electron-portal can account for the excess well and satisfy the DM relic density and direct detection bounds, while electron+muon/electron+muon+tau-portal suffers from strong constraints from lepton flavor violating observables, such as $\mu~\to~3~e$. We also discuss possible collider signatures of our model, both at the LHC and a future 100 TeV hadron collider.

Quantum Fisher information and coherence in one-dimensional XY spin models with Dzyaloshinsky-Moriya interactions

Abstract: We investigate quantum phase transitions in $XY$ spin models using Dzyaloshinsky-Moriya (DM) interactions.We identify the quantum critical points via quantum Fisher information and quantum coherence, finding that higherDM couplings suppress quantum phase transitions. However, quantum coherence (characterized by the $l_1$-norm and relative entropy)decreases as the DM coupling increases. Herein,we present bothanalytical and numerical results.

Analytic approximations of Von Kármán plate under arbitrary uniform pressure—equations in integral form

Abstract: Analytic approximations of the Von Karman’s plate equations in integral form for a circular plate under external uniform pressure to arbitrary magnitude are successfully obtained by means of the homotopy analysis method (HAM), an analytic approximation technique for highly nonlinear problems. Two HAM-based approaches are proposed for either a given external uniform pressure Q or a given central deflection, respectively. Both of them are valid for uniform pressure to arbitrary magnitude by choosing proper values of the so-called convergence-control parameters c 1 and c 2 in the frame of the HAM. Besides, it is found that the HAM-based iteration approaches generally converge much faster than the interpolation iterative method. Furthermore, we prove that the interpolation iterative method is a special case of the first-order HAM iteration approach for a given external uniform pressure Q when c 1 = −θ and c 2 = −1, where θ denotes the interpolation iterative parameter. Therefore, according to the convergence theorem of Zheng and Zhou about the interpolation iterative method, the HAM-based approaches are valid for uniform pressure to arbitrary magnitude at least in the special case c 1 = −θ and c 2 = −1. In addition, we prove that the HAM approach for the Von Karman’s plate equations in differential form is just a special case of the HAM for the Von Karman’s plate equations in integral form mentioned in this paper. All of these illustrate the validity and great potential of the HAM for highly nonlinear problems, and its superiority over perturbation techniques.

Simulation and detection of the topological properties of a modulated Rice-Mele model in a one-dimensional circuit-QED lattice

Abstract: Here, we propose a simple scheme to realize a one-dimensional (1D) modulated Rice-Mele model (RMM) and investigate its topological properties with a 1D circuit quantum electrodynamics (QED) lattice. The system can be mapped into a Chern insulator model by introducing a period parameter. Interestingly and surprisingly, we found that the circuit-QED lattice system always exhibits topologically nontrivial phases if both the nearest-neighbor hopping strength between two resonators and the qubit-assisted on-site potentials are alternately changed in the direction of the lattice. The numerical results show that the topological phases can be obtained by introducing an additional modulation parameter and both the edge state and topological invariant can be unambiguously seen with the existence of decay and disorders, even with few resonators in the lattice.

Holographic heat engine with momentum relaxation

Abstract: We investigate the heat engine defined via black hole with momentum relaxation, which is introduced by massless axion fields. We first study the extended thermodynamical properties of the black hole and then apply it to define a heat engine. Then, we analyze how the momentum relaxation affects the efficiency of the heat engine in the limit of high temperature. We find that depending on the schemes of specified parameters in the engine circle, the influence of momentum relaxation on the efficiency of the heat engine behaves novelly, and the qualitative behaviors do depend on the dimension of the gravity theory.

Disintegration of an eruptive filament via interactions with quasi-separatrix layers

Abstract: The disintegration of solar filaments via mass drainage is a frequently observed phenomenon during a variety of filament activities. It is generally considered that the draining of dense filament material is directed by both gravity and magnetic field, yet the detailed process remains elusive. Here we report on a partial filament eruption during which filament material drains downward to the surface not only along the filaments legs, but to a remote flare ribbon through a fan-out curtain-like structure. It is found that the magnetic configuration is characterized by two conjoining dome-like quasi-sepratrix layers (QSLs). The filament is located underneath one QSL dome, whose footprint apparently bounds the major flare ribbons resulting from the filament eruption, whereas the remote flare ribbon matches well with the other QSL domes far-side footprint. We suggest that the interaction of the filament with the overlying QSLs results in the splitting and disintegration of the filament.

Interaction between the atmospheric boundary layer and a stand-alone wind turbine in Gansu-Part II: Numerical analysis

Abstract: To analyze the interaction between wind turbines and the atmospheric boundary layer, we integrated a large-eddy simulation with an actuator line model and examined the characteristics of wind-turbine loads and wakes with reference to a corresponding experiment in Gansu. In the simulation, we set the wind turbine to have a rotor diameter of 14.8 m and a tower height of 15.4 m in the center of an atmospheric boundary layer with a 10.6A degrees yaw angle. The results reveal an obviously skewed wake structure behind the rotor due to the thrust component normal to the flow direction. The power spectra of the inflow fluctuation velocity exhibit a region of -5/3 slope, which confirms the ability of large-eddy simulations to reproduce the energy cascade from larger to smaller scales. We found there to be more energy in the power spectrum of the axial velocity, which shows that coherent turbulence structures have more energy in the horizontal direction. By the conjoint analysis of atmospheric turbulence and windturbine loads, we found that when the inflow wind direction changes rapidly, the turbulence kinetic energy and coherent turbulence kinetic energy in the atmospheric turbulence increase, which in turn causes fluctuations in the wind turbine load. Furthermore, anisotropic atmospheric turbulence causes an asymmetric load cycle, which imposes a strike by the turbine blade on the shaft, thereby increasing the fatigue load on the shaft. Our main conclusion is that the atmospheric boundary layer has a strong effect on the evolution of the wake and the structural response of the turbine.

NLO QCD corrections to B c ( B * c ) production around the Z pole at an e + e - collider

Abstract: The production of $B_c$ and $B_c^*$ mesons at a $Z$-factory (an $e^+e^-$ collider operating at energies around the $Z$ pole) is calculatedup to the next-to-leading order (NLO) QCD accuracy. The results show that the dependence of the total cross sections on the renormalization scale $\mu$ is suppressed by the corrections, and the NLO corrections enhance the total cross sections of $B_c$ by $52%$ and of $B_c^*$ by $33%$ when the renormalization scale is taken at $\mu=2m_b$. To observe the various behaviors of the production of the mesons $B_c$ and $B_c^*$, such as the differential cross section vs. the out-going angle, the forward-backward asymmetry, and the distribution vs. the energy fraction $z$ up to NLO QCD accuracy as well as the relevant $K$-factor (NLO to LO) for the production, are calculated, and it is pointed out that some of the observables obtained in the present work may be used as a specific precision test of the standard model.

Strong Matter: Rethinking Philosophically

Abstract: Normal condensed matter is merely of electromagnetic interaction. A novel state of strong-interaction matter is revisited.

Thermally activated flux flow, vortex-glass phase transition and the mixed-state Hall effect in 112-type iron pnictide superconductors

Abstract: The transport properties in the mixed state of high-quality Ca08La02Fe098Co002As2 single crystal, a newly discovered 112-type iron pnictide superconductor, are comprehensively studied by magneto-resistivity measurement The field-dependent activation energy, U0, is derived in the framework of thermally activated flux flow (TAFF) theory, yielding a power law dependence U0~Hα with a crossover at a magnetic field around 2 T in both H⊥ab and H//ab, which is ascribed to the different pinning mechanisms Moreover, we have clearly observed the vortex phase transition from vortex-glass to vortex-liquid according to the vortex-glass model, and vortex phase diagrams are constructed for both H⊥ab and H//ab Finally, the results of mixed-state Hall effect show that no sign reversal of transverse resistivity ρxy(H) is detected, indicating that the Hall component arising from the vortex flow is also negative based on the time dependent Ginzburg-Landau (TDGL) theory Meanwhile, the transverse resistivity ρxy(H) and the longitudinal resistivity ρxx(H) follow the relation |ρxy(H)|=Aρxx(H)β well with an exponent β~20, which is in line with the results in theories or experiments previously reported on some high-Tc cuprates

Signal-background discrimination with convolutional neural networks in the PandaX-III experiment using MC simulation

Abstract: The PandaX-III experiment will search for neutrinoless double beta decay of $^{136}$Xe with high pressure gaseous time projection chambers at the China Jin-Ping underground Laboratory. The tracking feature of gaseous detectors helps suppress the background level, resulting in the improvement of the detection sensitivity. We study a method based on the convolutional neural networks to discriminate double beta decay signals against the background from high energy gammas generated by $^{214}$Bi and $^{208}$Tl decays based on detailed Monte Carlo simulation. Using the 2-dimensional projections of recorded tracks on two planes, the method successfully suppresses the background level by a factor larger than 100 with a high signal efficiency. An improvement of$62%$ on the efficiency ratio of $\epsilon_{s}/\sqrt{\epsilon_{b}}$ is achieved in comparison with the baseline in the PandaX-III conceptual design report.