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Showing papers in "Science China-physics Mechanics & Astronomy in 2021"


Journal ArticleDOI
TL;DR: In this article, the magnetic penetration depth of the kagome metal series AV3Sb5 (A=K, Rb, Cs) was measured down to 0.07 K.
Abstract: The recently discovered kagome metal series AV3Sb5 (A=K, Rb, Cs) exhibits topologically nontrivial band structures, chiral charge order and superconductivity, presenting a unique platform for realizing exotic electronic states. The nature of the superconducting state and the corresponding pairing symmetry are key questions that demand experimental clarification. Here, using a technique based on the tunneling diode oscillator, the magnetic penetration depth Δλ(T) of CsV3Sb5 was measured down to 0.07 K. A clear exponential behavior in Δλ(T) with marked deviations from a T or T2 temperature dependence was observed at low temperatures, indicating an absence of nodal quasiparticles. Temperature dependence of the superfluid density and electronic specific heat can be described by two-gap s-wave superconductivity, consistent with the presence of multiple Fermi surfaces in CsV3Sb5. These results evidence nodeless superconductivity in CsV3Sb5 under ambient pressure, and constrain the allowed pairing symmetry.

91 citations


Journal ArticleDOI
TL;DR: In this article, an erbium-doped LNOI laser in the 1550-nm band was demonstrated in microdisk cavities with high quality factors fabricated in batches by UV exposure, inductively coupled plasma reactive ion etching, and chemomechanical polishing.
Abstract: Lithium niobate on insulator (LNOI) provides a platform for the fundamental physics investigations and practical applications of integrated photonics. However, as an indispensable building block of integrated photonics, lasers are in short supply. In this paper, erbium-doped LNOI laser in the 1550-nm band was demonstrated in microdisk cavities with high quality factors fabricated in batches by UV exposure, inductively coupled plasma reactive ion etching, and chemomechanical polishing. The threshold and conversion efficiency of the erbium-doped LNOI microdisk laser were measured to be lower than 1 mW and 6.5×10−5%, respectively. This work will benefit the development of integrated photonics based on LNOI.

65 citations


Journal ArticleDOI
TL;DR: In this article, the authors summarize the basic physics of FRBs and discuss the current research progress in this area, including the observational property, propagation effect, population study, radiation mechanism, source model, and application in cosmology.
Abstract: In 2007, a very bright radio pulse was identified in the archival data of the Parkes Telescope in Australia, marking the beginning of a new research branch in astrophysics. In 2013, this kind of millisecond bursts with extremely high brightness temperature takes a unified name, fast radio burst (FRB). Over the first few years, FRBs seemed very mysterious because the sample of known events was limited. With the improvement of instruments over the last five years, hundreds of new FRBs have been discovered. The field is now undergoing a revolution and understanding of FRB has rapidly increased as new observational data increasingly accumulate. In this review, we will summarize the basic physics of FRBs and discuss the current research progress in this area. We have tried to cover a wide range of FRB topics, including the observational property, propagation effect, population study, radiation mechanism, source model, and application in cosmology. A framework based on the latest observational facts is now under construction. In the near future, this exciting field is expected to make significant breakthroughs.

63 citations


Journal ArticleDOI
TL;DR: The holographic axion model as mentioned in this paper is a bottom-up holographic system characterized by the presence of a set of shift symmetric scalar bulk fields whose profiles are taken to be linear in the spatial coordinates.
Abstract: This is a complete and exhaustive review on the so-called holographic axion model—a bottom-up holographic system characterized by the presence of a set of shift symmetric scalar bulk fields whose profiles are taken to be linear in the spatial coordinates. This simple model implements the breaking of translational invariance of the dual field theory by retaining the homogeneity of the background geometry and therefore allowing for controllable and fast computations. The usages of this model are very vast and they are a proof of the spectacular versatility of the framework. In this review, we touch upon all the up-to-date aspects of this model from its connection with massive gravity and effective field theories, to its role in modeling momentum dissipation and elastic properties ending with all the phenomenological features and its hydrodynamic description. In summary, this is a complete guide to one of the most used models in Applied Holography and a must-read for any researcher entering this field.

59 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that the pure gauge operators of dimension-8 can generate ZγZ* and Zγγ* vertices with rapid energy dependence ∈ E5, which can be probed sensitively via the reaction e+e− → Zγ.
Abstract: Neutral triple gauge couplings (nTGCs) are absent in the standard model effective theory up to dimension-6 operators, but could arise from dimension-8 effective operators. In this work, we study the pure gauge operators of dimension-8 that contribute to nTGCs and are independent of the dimension-8 operator involving the Higgs doublet. We show that the pure gauge operators generate both ZγZ* and Zγγ* vertices with rapid energy dependence ∝ E5, which can be probed sensitively via the reaction e+e− → Zγ. We demonstrate that measuring the nTGCs via the reaction e+e− → Zγ followed by $$Z\rightarrow q\bar{q}$$ decays can probe the new physics scales of dimension-8 pure gauge operators up to the range (1-5) TeV at the CEPC, FCC-ee and ILC colliders with $$\sqrt{s}=(0.25-1)$$ TeV, and up to the range (10–16) TeV at CLIC with $$\sqrt{s}=(3-5)$$ TeV, assuming in each case an integrated luminosity of 5 ab−1. We compare these sensitivities with the corresponding probes of the dimension-8 nTGC operators involving Higgs doublets and the dimension-8 fermionic contact operators that contribute to the e+e−Zγ vertex.

47 citations


Journal ArticleDOI
TL;DR: In this article, a 1-mol% erbium-doped lithium niobate crystal and its LNOI on a silicon substrate was developed and a 1.05×105-nm laser emission at ∼1530 and ∼1560 nm (linewidth 0.12 nm) was demonstrated with 974- and 1460-nm pumping, with the latter having better thermal stability.
Abstract: The commercialization of lithium niobate on insulator (LNOI) wafer has resulted in significant on-chip photonic integration application owing to its remarkable photonic, acousto-optic, electro-optic, and piezoelectric nature. In recent years, a variety of high-performance on-chip LNOI-based photonic devices have been realized. In this study, we developed a 1-mol% erbium-doped lithium niobate crystal and its LNOI on a silicon substrate and fabricated an erbium-doped LNOI microdisk with high quality factor (∼ 1.05×105). C-band laser emission at ∼1530 and ∼1560 nm (linewidth 0.12 nm) from the high-Q erbium-doped LNOI microdisk was demonstrated with 974- and 1460-nm pumping, with the latter having better thermal stability. This microlaser would play an important role in the photonic integrated circuits of the lithium niobate platform.

44 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the dynamic phase behavior at a black hole triple point and found that initial small, intermediate, or large black holes can transit to the other two coexistent phases at the triple point, indicating that thermodynamic phase transitions can indeed occur dynamically.
Abstract: Understanding the dynamic process of black hole thermodynamic phase transitions at a triple point is a huge challenge. In this paper, we conduct the first investigation of dynamic phase behavior at a black hole triple point. By numerically solving the Smoluchowski equation near the triple point for a six-dimensional charged Gauss-Bonnet anti-de Sitter black hole, we report that initial small, intermediate, or large black holes can transit to the other two coexistent phases at the triple point, indicating that thermodynamic phase transitions can indeed occur dynamically. More significantly, we observe characteristic weak and strong oscillatory behavior in this dynamic process, which can be understood from an investigation of the rate of first passage from one phase to another. Our results further an understanding of the dynamic process of black hole thermodynamic phase transitions.

38 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the entanglement and EPR steering between two macroscopic magnons in a hybrid ferrimagnet-light system and found that in the absence of light, the two types of magnons on the two sublattices can be entangled, but no quantum steering occurs when they are damped with the same rates.
Abstract: The generation and manipulation of strong entanglement and Einstein-Podolsky-Rosen (EPR) steering in macroscopic systems are outstanding challenges in modern physics. Especially, the observation of asymmetric EPR steering is important for both its fundamental role in interpreting the nature of quantum mechanics and its application as resource for the tasks where the levels of trust at different parties are highly asymmetric. Here, we study the entanglement and EPR steering between two macroscopic magnons in a hybrid ferrimagnet—light system. In the absence of light, the two types of magnons on the two sublattices can be entangled, but no quantum steering occurs when they are damped with the same rates. In the presence of the cavity field, the entanglement can be significantly enhanced, and strong two-way asymmetric quantum steering appears between two magnons with equal dissipation. This is very different from the conventional protocols to produce asymmetric steering by imposing additional unbalanced losses or noises on the two parties at the cost of reducing steerability. The essential physics is well understood by the unbalanced population of acoustic and optical magnons under the cooling effect of cavity photons. Our finding may provide a novel platform to manipulate the quantum steering and the detection of bi-party steering provides a knob to probe the magnetic damping on each sublattice of a magnet.

37 citations


Journal ArticleDOI
TL;DR: In this paper, the authors discuss a special form of coherence singularity, ring dislocation, mathematically and physically and provide a feasible approach to measure mode indices of PCVBs.
Abstract: It has been over 30 years since the concept of optical vortices was first proposed by Coullet et al. in 1989, and the field of structured beams has grown extremely. In the last two decades, partially coherent vortex beams (PCVBs) have received increasing interest in the fields of optical manipulation, optical communication, optical imaging, etc., and great progress has been made in the area of the coherence singularities, generation methods, topological charge measurements, and promising applications of PCVBs. In this review, we firstly outline the basic concepts of PCVBs. We explicate the relationship between the coherence vortices and optical vortices, and the evolution behavior of optical vortices to coherence vortices is summarized in detail. We discuss a special form of coherence singularity, ring dislocation, mathematically and physically. The ring dislocation in the correlation functions under low coherence is dependent on the mode indices, which provide a feasible approach to measure mode indices of PCVBs. Subsequently, we summarize the various methods for measuring the topological charge of PCVBs, highlight the measurement method based on the cross-correlation function, and a physical explanation on the relation between ring dislocation and topological charge is given. After that, we review the recent advances on experimental generation of several kinds of PCVBs. Lastly, we give an overview on the potential applications of PCVBs.

37 citations


Journal ArticleDOI
TL;DR: In this paper, a simple quasi-continuous monolayer graphene structure was proposed to achieve a dynamically tunable triple plasmon-induced transparency (PIT) effect in the proposed structure.
Abstract: We propose a simple quasi-continuous monolayer graphene structure and achieve a dynamically tunable triple plasmon-induced transparency (PIT) effect in the proposed structure. Additional analyses indicate that the proposed structure contains a self-constructed bright-dark-dark mode system. A uniform theoretical model is introduced to investigate the spectral response characteristics and slow light-effects in the proposed system, and the theoretical and the simulated results exhibit high consistency. In addition, the influences of the Fermi level and the carrier mobility of graphene on transmission spectra are discussed. It is found that each PIT window exhibits an independent dynamical adjustability owing to the quasi-continuity of the proposed structure. Finally, the slow-light effects are investigated based on the calculation of the group refractive index and phase shift. It is found that the structure displays excellent slow-light effects near the PIT windows with high-group indices, and the maximum group index of each PIT window exceeds 1000 when the carrier mobility of graphene increases to 3.5 m2 V−1 s−1. The proposed structure has potential to be used in multichannel filters, optical switches, modulators, and slow light devices. Additionally, the established theoretical model lays a theoretical basis for research on multimode coupling effects.

32 citations


Journal ArticleDOI
TL;DR: In this article, a DNN-based HSL-TFP surrogate modeling task benchmark is proposed, with consideration for engineering applicability, sample generation, dataset evaluation, DNN model, and surrogate performance metrics are thoroughly investigated.
Abstract: The thermal issue is of great importance during the layout design of heat source components in systems engineering, especially for high functional-density products. Thermal analysis requires complex simulation, which leads to an unaffordable computational burden to layout optimization as it iteratively evaluates different schemes. Surrogate modeling is an effective method for alleviating computation complexity. However, the temperature field prediction (TFP) with complex heat source layout (HSL) input is an ultra-high dimensional nonlinear regression problem, which brings great difficulty to traditional regression models. The deep neural network (DNN) regression method is a feasible way for its good approximation performance. However, it faces great challenges in data preparation for sample diversity and uniformity in the layout space with physical constraints and proper DNN model selection and training for good generality, which necessitates the efforts of layout designers and DNN experts. To advance this cross-domain research, this paper proposes a DNN-based HSL-TFP surrogate modeling task benchmark. With consideration for engineering applicability, sample generation, dataset evaluation, DNN model, and surrogate performance metrics are thoroughly investigated. Experiments are conducted with ten representative state-of-the-art DNN models. A detailed discussion on baseline results is provided, and future prospects are analyzed for DNN-based HSL-TFP tasks.

Journal ArticleDOI
TL;DR: In this article, the authors performed dynamic mechanical analysis and thermal creep on a bulk metallic glass material at a temperature domain around the β relaxation, including ideal elastic strain, anelastic strain, and viscous-plastic strain.
Abstract: Dynamic mechanical relaxation is a fundamental tool to understand the mechanical and physical properties of viscoelastic materials like glasses. Mechanical spectroscopy shows that the high-entropy bulk metallic glass (La30Ce30Ni10Al20Co10) exhibits a distinct β-relaxation feature. In the present research, dynamic mechanical analysis and thermal creep were performed using this bulk metallic glass material at a temperature domain around the β relaxation. The components of total strain, including ideal elastic strain, anelastic strain, and viscous-plastic strain, were analyzed based on the model of shear transformation zones (STZs). The stochastic activation of STZ contributes to the anelastic strain. When the temperature or external stress is high enough or the timescale is long enough, the interaction between STZs induces viscous-plastic strain. When all the spectrum of STZs is activated, the quasi-steady-state creep is achieved.

Journal ArticleDOI
Bofeng Gao1, Mengxin Ren2, Mengxin Ren1, Wei Wu1, Wei Cai1, Jingjun Xu1 
TL;DR: In this article, an electro-optic lithium niobate (EO-LN) metasurface has been developed for displaying, pulse shaping, and spatial light modulating.
Abstract: Many applications of metasurfaces require an ability to dynamically change their properties in the time domain Electrical tuning techniques are of particular interest, since they pave a way to on-chip integration of metasurfaces with optoelectronic devices In this work, we propose and experimentally demonstrate an electro-optic lithium niobate (EO-LN) metasurface that shows dynamic modulations to phase retardation of transmitted light Quasi-bound states in the continuum (QBIC) are observed from this metasurface By applying external electric voltages, the refractive index of lithium niobate (LN) is changed by Pockels EO nonlinearity, leading to efficient phase modulations to the transmitted light around the QBIC wavelength The EO-LN metasurface developed in this study opens up new routes for potential applications in the field of displaying, pulse shaping, and spatial light modulating

Journal ArticleDOI
TL;DR: In this article, the authors show that the NANOGrav evidence of a common-source stochastic background provides a hint to gravitational waves (GW) radiation from the Early Universe.
Abstract: The recent NANOGrav evidence of a common-source stochastic background provides a hint to gravitational waves (GW) radiation from the Early Universe. We show that this result can be interpreted as a GW spectrum produced from first order phase transitions (FOPTs) around a temperature in the keV-MeV window. Such a class of FOPTs at temperatures much below the electroweak scale can be naturally envisaged in several warm dark matter models such as Majoron dark matter.

Journal ArticleDOI
TL;DR: In this paper, a perspective review over the recent development of short-pulsed Raman fiber laser (RFLs), which can provide laser emissions with flexible wavelengths for a variety of applications as well as an excellent platform to investigate various nonlinear pulse dynamics behaviors that cannot be captured in conventional rare-earth (RE) doped counterparts, is provided.
Abstract: We provide a perspective review over the recent development of short-pulsed Raman fiber lasers (RFLs), which can provide laser emissions with flexible wavelengths for a variety of applications as well as an excellent platform to investigate various nonlinear pulse dynamics behaviors that cannot be captured in conventional rare-earth (RE) doped counterparts Various pulse generation techniques have been explored in RFLs However, the output pulse performance in terms of the pulse energy, duration and stability from short-pulsed RFLs is still inferior to their RE-doped counterparts despite significant advances made over the past few decades Therefore, more efforts are required to improve these targets In this review, we present a detailed overview of the short-pulsed RFLs based on different mechanisms from the principle to the experiment, including the Q-switching, gain-switching, mode-locking, synchronous pumping and other innovative techniques In addition, Raman-induced pulse dynamics in ultrafast RFLs and RE-doped mode-locked fiber lasers (MLFLs) are briefly reviewed Finally, a perspective outlook for the future ultrafast RFLs is provided based on their potential applications in industrial and scientific research areas

Journal ArticleDOI
TL;DR: The first search for an isotropic non-tensorial GWB allowed in general metric theories of gravity in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 12.5-year data set was performed in this paper.
Abstract: We perform the first search for an isotropic non-tensorial gravitational-wave background (GWB) allowed in general metric theories of gravity in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 12.5-year data set. By modeling the GWB as a power-law spectrum, we find strong Bayesian evidence for a spatially correlated process with scalar transverse (ST) correlations whose Bayes factor versus the spatially uncorrelated common-spectrum process is $99\pm 7$, but no statistically significant evidence for the tensor transverse, vector longitudinal and scalar longitudinal polarization modes. The median and the $90\%$ equal-tail amplitudes of ST mode are $\mathcal{A}_{\mathrm{ST}}= 1.06^{+0.35}_{-0.28} \times 10^{-15}$, or equivalently the energy density parameter per logarithm frequency is $\Omega_{\mathrm{GW}}^{\mathrm{ST}} = 1.54^{+1.20}_{-0.71} \times 10^{-9}$, at frequency of 1/year.

Journal ArticleDOI
TL;DR: In this article, an electrical circuit is constructed to realize a modified Haldane lattice exhibiting the phenomenon of antichiral edge states, where the next nearest neighbor hoppings are configured differently from the standard HaldANE model, and as predicted by earlier theoretical studies, this gives rise to Antichiral Edge states that propagate in the same direction on opposite edges and coexist with bulk states at the same frequency.
Abstract: We construct an electrical circuit to realize a modified Haldane lattice exhibiting the phenomenon of antichiral edge states. The circuit consists of a network of inductors and capacitors with interconnections reproducing the effects of a magnetic vector potential. The next nearest neighbor hoppings are configured differently from the standard Haldane model, and as predicted by earlier theoretical studies, this gives rise to antichiral edge states that propagate in the same direction on opposite edges and coexist with bulk states at the same frequency. Using pickup coils to measure voltage distributions in the circuit, we experimentally verify the key features of the antichiral edge states, including their group velocities and ability to propagate consistently in a Mobius strip configuration.

Journal ArticleDOI
TL;DR: It is highlighted that a dishonest participant can obtain a sender’s secret message alone without introducing any detectable error, evidencing the vulnerability of the MDI-QSS protocol to the participant attack.
Abstract: In a recent article [Gao et al., Sci. China-Phys. Mech. Astron. 63, 120311 (2020)], a two-receiver measurement-device-independent quantum secret sharing (MDI-QSS) protocol was presented. It was proven to be secure against eavesdropping and generalized to the multireceiver case. However, the participant attack is a fatal threat to QSS protocols. Here, we highlight that a dishonest participant can obtain a sender’s secret message alone without introducing any detectable error, evidencing the vulnerability of the MDI-QSS protocol to the participant attack.

Journal ArticleDOI
TL;DR: In this paper, the authors search for metal-rich Sausage-kinematic (MRSK) stars with [Fe/H] > −0.8 and −100 < Vφ < 50 km/s in LAMOST DR5 in order to investigate the influence of the Gaia-Sausage Enceladus (GSE) merger event on the Galactic disk.
Abstract: We search for metal-rich Sausage-kinematic (MRSK) stars with [Fe/H] > −0.8 and −100 < Vφ < 50 km/s in LAMOST DR5 in order to investigate the influence of the Gaia-Sausage-Enceladus (GSE) merger event on the Galactic disk. For the first time, we find a group of low-α MRSK stars, and classify it as a metal-rich tail of the GSE galaxy based on the chemical and kinematical properties. This group has slightly larger Rapo, Zmax and Etot distributions than a previously-reported high-α group. Its low-α ratio does not allow for an origin resulting from the splash process of the GSE merger event, as is proposed to explain the high-α group. A hydrodynamical simulation by Amarante et al. provides a promising solution, in which the GSE galaxy is a clumpy Milky-Way analogue that develops a bimodal disk chemistry. This scenario explains the existence of MRSK stars with both high-α and low-α ratios found in this work. It is further supported by another new feature that a clump of MRSK stars is located at Zmax=3−5 kpc, which corresponds to the widely adopted disk-halo transition at ∣Z∣ ∼ 4 kpc. We suggest that a pile-up of MRSK stars at Zmax contributes significantly to this disk-halo transition, an interesting imprint left by the GSE merger event. These results also provide an important implication on the connection between the GSE and the Virgo Radial Merger.

Journal ArticleDOI
TL;DR: In this paper, a two-decoy-state protocol was proposed to solve the problem of photon-number-splitting attacks caused by the use of attenuated lasers in quantum secure direct communication (QSDC).
Abstract: Quantum secure direct communication (QSDC) has been demonstrated in both fiber-based and free-space channels using attenuated lasers. Decoy-state QSDC by exploiting four decoy states has been proposed to address the problem of photon-number-splitting attacks caused by the use of attenuated lasers. In this study, we present an analysis of the practical aspects of decoy-state QSDC. First, we design a two-decoy-state protocol that only requires two decoy states, thereby significantly reducing experimental complexity. Second, we successfully perform full parameter optimization for a real-life QSDC system by introducing a genetic algorithm. Our simulation results show that the two-decoy-state protocol could be the best choice for developing a practical QSDC system. Furthermore, full optimization is crucial for a high-performance QSDC system. Our work serves as a major step toward the further development of practical decoy-state QSDC systems.

Journal ArticleDOI
TL;DR: In this article, the authors employed a machine learning-accelerated crystal structure searching method and first-principles calculations, and found that the new pentazolate salts, CaN10 and BaN10, are energetically favorable at high pressures.
Abstract: The search for high energy density materials (HEDMs) in polymeric nitrogen compounds has gained considerable attention. Previous theoretical predictions and experiments have revealed that metal ions can be used to stabilize the pentazolate (N 5 − ) anion. In this work, by employing a machine learning-accelerated crystal structure searching method and first-principles calculations, we found that the new pentazolate salts, CaN10 and BaN10, are energetically favorable at high pressures. Phonon dispersion calculations reveal that they are quenchable at ambient pressure. Ab initio molecular dynamics simulations verify their dynamic stability at finite temperature. Bader charge and electron localization function illustrates that alkaline earth atoms serve as electron donors, contributing to the stability of N5 rings. Bonding calculations reveal covalent bonds between nitrogen atoms and weak interactions between N5 rings. Similar to other pentazolate salts, these polymeric nitrides have high energy densities of approximately 2.35 kJ/g for CaN10 and 1.32 kJ/g for BaN10. The predictions of CaN10 and BaN10 structures indicate that these salts are potential candidates for green nitrogen-rich HEDMs.

Journal ArticleDOI
TL;DR: In this article, the Vernier effect was applied to two coupled erbium-doped LNOI microrings with different radii under the pump of a 980-nm continuous laser.
Abstract: Microcavity lasers based on erbium-doped lithium niobate on insulator (LNOI), which are key devices for LNOI integrated photonics, have attracted significant attention recently. In this study, we report the realization of a C-band single-mode laser using the Vernier effect in two coupled erbium-doped LNOI microrings with different radii under the pump of a 980-nm continuous laser. The laser, operating stably over a large range of pumping power, has a pump threshold of about 200 µW and a side-mode suppression ratio exceeding 26 dB. The high-performance LNOI single-mode laser will promote the development of lithium niobate integrated photonics.

Journal ArticleDOI
TL;DR: In this paper, the authors refreshed the calibration of multiple measurements of high-redshift quasars (in the framework of a cosmological-model-independent method with the newest Hubble parameters data).
Abstract: Recently, two classes of quasar samples were identified, which are promising as new cosmological probes extending to higher redshifts. The first sample uses the nonlinear relation between the ultraviolet and X-ray luminosities of quasars to derive luminosity distances, whereas the linear sizes of compact radio quasars in the second sample can serve as standardized rulers, providing angular-diameter distances. In this study, under the assumption of a flat universe, we refreshed the calibration of multiple measurements of high-redshift quasars (in the framework of a cosmological-model-independent method with the newest Hubble parameters data). Furthermore, we placed constraints on four models that characterize the cosmic equation of state (w). The obtained results show that: (1) the two quasar samples could provide promising complementary probes at much higher redshifts, whereas compact radio quasars perform better than ultraviolet and X-ray quasars at the current observational level; (2) strong degeneracy between the cosmic equation of state (w) and Hubble constant (H0) is revealed, which highlights the importance of independent determination of H0 from time-delay measurements of strongly lensed quasars; (3) together with other standard ruler probes, such as baryon acoustic oscillation distance measurements, the combined QSO+BAO measurements are consistent with the standard ΛCDM model at a constant equation of state w = −1; (4) ranking the cosmological models, the polynomial parametrization gives a rather good fit among the four cosmic-equation-of-state models, whereas the Jassal-Bagla-Padmanabhan (JBP) parametrization is substantially penalized by the Akaike Information Criterion and Bayesian Information Criterion.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate the effects of quantum anomalous energy (QAE) in QED, as well as in a toy 1 + 1 dimensional non-linear sigma model where it contributes non-perturbatively, in a way resembling the Higgs mechanism for the masses of matter particles in electro-weak theory.
Abstract: Apart from the quark and gluon kinetic and potential energies, the nucleon mass includes a novel energy of pure quantum origin resulting from anomalous breaking of scale symmetry. We demonstrate the effects of this quantum anomalous energy (QAE) in QED, as well as in a toy 1 + 1 dimensional non-linear sigma model where it contributes non-perturbatively, in a way resembling the Higgs mechanism for the masses of matter particles in electro-weak theory. The QAE contribution to the nucleon mass can be explained using a similar mechanism, in terms of a dynamical response of the gluonic scalar field through Higgs-like couplings between the nucleon and scalar resonances. In addition, the QAE sets the scale for other energies in the nucleon through a relativistic virial theorem, and contributes a negative pressure to confine the colored quarks.

Journal ArticleDOI
TL;DR: In this paper, a resonantly coupled plasmonic-photonic cavity can boost the efficiency of single-photon generation by more than three orders of magnitude compared with that of all-dielectric microcavity.
Abstract: The generation and manipulation of single photons are crucial in advanced quantum technologies, such as quantum communication and quantum computation devices. High-purity single photons can be generated from classical light using the single-photon blockade (1PB). However, the efficiency and purity are exclusive in 1PB, which hinders its practical applications. Here, we show that the resonantly coupled plasmonic-photonic cavity can boost the efficiency of single-photon generation by more than three orders of magnitude compared with that of all-dielectric microcavity. This significant improvement is attributed to two new mechanisms of atom-microcavity coupling after introducing the plasmonic cavity: the formation of a quasi-bound state and the transition to the nonreciprocal regime, due to the destructive interference between the coupling pathways and the nonzero relative phase of the closed-loop coupling, respectively. The quasi-bound state has a relatively small decaying, while its effective coupling strength is significantly enhanced. Suppressing the dissipative component of the effective atom-microcavity coupling in the nonreciprocal regime can further improve single-photon performance, particularly without temporal oscillations. Our study demonstrates the possibility of enhancing the intrinsically low efficiency of 1PB in low excitation regime, and unveils the novel light-matter interaction in hybrid cavities.

Journal ArticleDOI
Qing Li1, Chengping He1, Xiyu Zhu1, Jin Si1, Xinwei Fan1, Hai-Hu Wen1 
TL;DR: In this paper, the crystal structures and physical properties of trilayer nickelates Nd4Ni3O10 and Nd 4 Ni3O8 have been reported and the magnetic properties of the two compounds have been investigated.
Abstract: We report the crystal structures and physical properties of trilayer nickelates Nd4Ni3O10 and Nd4Ni3O8. Measurements of magnetization and electrical resistivity display contrasting behaviors in the two compounds. Nd4Ni3O10 shows a paramagnetic metallic behavior with a metal-to-metal phase transition ( T ∗) at about 162 K, as revealed by both magnetic susceptibility and resistivity. Further magnetoresistance and Hall coefficient results show a negative magnetoresistance at low temperatures and the carrier type of Nd4Ni3O10 is dominated by hole-type charge carriers. The significant enhancement of Hall coefficient and resistivity below T ∗ suggests that effective charge carrier density decreases when cooling through the transition temperature. In contrast, Nd4Ni3O8 shows an insulating behavior. In addition, this compound shows a paramagnetic behavior with the similar magnetic moment as that of Nd4Ni3O10 derived from the Curie-Weiss fitting. This may suggest that the magnetic moments in both systems are contributed by Nd3+ ions. By applying pressures up to about 49 GPa, the insulating behavior is still present and becomes even stronger under a high pressure. Our results suggest that the different Ni configurations (Ni1+/2+ or Ni2+/3+) and the changes of coordination environment of Ni sites may account for the contrasting behaviors in trilayer nickelates Nd4Ni3O10 and Nd4Ni3O8.

Journal ArticleDOI
TL;DR: In this paper, the atomistic mechanism of spin-lattice coupling in spintronic applications is explored based on the density functional theory, and it is shown that the first and second-order SL couplings in ternary system CrGeTe3 are considerably stronger than those in binary system CrI3.
Abstract: Spin-lattice (SL) coupling plays an important role in spintronic applications given its effects on magnetic, ferroelectric, optical, and thermodynamic properties. Experiments and theoretical calculations have revealed a large SL coupling effect in CrGeTe3 and CrI3 monolayers. However, the microscopic origin of SL coupling in these systems is still unclear. In this work, we develop a systematic method to explore the atomistic mechanism of SL coupling based on the density functional theory. We find that the first- and second-order SL couplings in ternary system CrGeTe3 are considerably stronger than those in binary system CrI3. For the first-order SL coupling, the Cr ions of the magnetic pair and Ge ions positively contribute to the strain enhancement of ferromagnetism in CrGeTe3. However, the Cr ions provide a negative contribution in CrI3. Furthermore, our tight-binding analysis suggests that the p-d hopping in CrGeTe3 gradually decreases with the tensile strain, rapidly enhancing the ferromagnetism under the tensile strain. The large frequency shifts in CrGeTe3 are caused by the large second-order exchange derivatives (one type of second-order SL coupling) of the Cr ions of the magnetic pair.

Journal ArticleDOI
TL;DR: In this paper, an Abelian-geometric-phase-based nonadiabatic geometric one-qubit gates with a superconducting Xmon qubit were demonstrated.
Abstract: Geometric phases are only dependent on evolution paths but independent of evolution details so that they possess some intrinsic noise-resilience features. Based on different geometric phases, various quantum gates have been proposed, such as nonadiabatic geometric gates based on nonadiabatic Abelian geometric phases and nonadiabatic holonomic gates based on nonadiabatic non-Abelian geometric phases. Up to now, nonadiabatic holonomic one-qubit gates have been experimentally demonstrated with superconducting transmons, where the three lowest levels are all utilized in operation. However, the second excited state of transmons has a relatively short coherence time, which results in a decreased fidelity of quantum gates. Here, we experimentally realize Abelian-geometric-phase-based nonadiabatic geometric one-qubit gates with a superconducting Xmon qubit. The realization is performed on the two lowest levels of an Xmon qubit and thus avoids the influence from the short coherence time of the second excited state. The experimental result indicates that the average fidelities of single-qubit gates can be up to 99.6% and 99.7% characterized by quantum process tomography and randomized benchmarking.

Journal ArticleDOI
TL;DR: In this article, the response of ultraflat bands to lattice relaxation and a magnetic field in twisted trilayer graphene (tTLG) with different stacking arrangements is investigated by using a full tight-binding model.
Abstract: Twisted graphene multilayers exhibit strongly correlated insulating states and superconductivity due to the presence of ultraflat bands near the charge neutral point. In this paper, the response of ultraflat bands to lattice relaxation and a magnetic field in twisted trilayer graphene (tTLG) with different stacking arrangements is investigated by using a full tight-binding model. We show that lattice relaxations are indispensable for understanding the electronic properties of tTLG, in particular, of tTLG in the presence of mirror symmetry. Lattice relaxations renormalize the quasiparticle spectrum near the Fermi energy and change the localization of higher energy flat bands. Furthermore, different from the twisted bilayer graphene, the Hofstadter butterfly spectrum can be realized at laboratory accessible strengths of magnetic field. Our work verifies tTLG as a more tunable platform than the twisted bilayer graphene in strongly correlated phenomena.

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TL;DR: In this article, the meridional circulation of the Sun is modeled as an axisymmetric 2D mean field theory, where the mean values of various quantities averaged over turbulence are assumed to be axisymetric, and the large-scale flows in solar-like stars are studied.
Abstract: The meridional circulation of the Sun, which is observed to be poleward at the surface, should have a return flow at some depth. Since large-scale flows like the differential rotation and the meridional circulation are driven by turbulent stresses in the convection zone, these flows are expected to remain confined within this zone. Current observational (based on helioseismology) and theoretical (based on dynamo theory) evidences point towards an equatorward return flow of the meridional circulation at the bottom of the convection zone. Assuming the mean values of various quantities averaged over turbulence to be axisymmetric, we study the large-scale flows in solar-like stars on the basis of a 2D mean field theory. Turbulent stresses in a rotating star can transport angular momentum, setting up a differential rotation. The meridional circulation arises from a slight imbalance between two terms which try to drive it in opposite directions: a thermal wind term (arising out of the higher efficiency of convective heat transport in the polar regions) and a centrifugal term (arising out of the differential rotation). To make these terms comparable, the poles of the Sun should be slightly hotter than the equator. We discuss the important role played by the meridional circulation in the flux transport dynamo model. The poloidal field generated by the Babcock-Leighton process at the surface is advected poleward, whereas the toroidal field produced at the bottom of the convection zone is advected equatorward. The fluctuations in the meridional circulation (with coherence time of about 30–40 yr) help in explaining many aspects of the irregularities in the solar cycle. Finally, we discuss how the Lorentz force of the dynamo-generated magnetic field can cause periodic variations in the large-scale flows with the solar cycle.