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Tao Li

Publications and source records attributed to Tao Li.

At least 487 records · Page 27Linked to original sources
arXiv2018

Alpha decay in intense laser fields: Calculations using realistic nuclear potentials

We calculate the effect of intense laser fields on nuclear alpha decay processes, using realistic and quantitative nuclear potentials. We show that alpha decay rates can indeed be modified by strong laser fields to some finite extent. We also predict that alpha decays with lower decay energies are relatively easier to be modified than those with higher decay energies, due to longer tunneling paths for the laser field to act on. Furthermore, we predict that modifications to angle-resolved penetrability are easier to achieve than modifications to angle-integrated penetrability.

physics.atom-ph↗
arXiv2018

YouTube AV 50K: An Annotated Corpus for Comments in Autonomous Vehicles

With one billion monthly viewers, and millions of users discussing and sharing opinions, comments below YouTube videos are rich sources of data for opinion mining and sentiment analysis. We introduce the YouTube AV 50K dataset, a freely-available collections of more than 50,000 YouTube comments and metadata below autonomous vehicle (AV)-related videos. We describe its creation process, its content and data format, and discuss its possible usages. Especially, we do a case study of the first self-driving car fatality to evaluate the dataset, and show how we can use this dataset to better understand public attitudes toward self-driving cars and public reactions to the accident. Future developments of the dataset are also discussed.

cs.CL↗
arXiv2018

On the longitudinal momentum of the electron at the tunneling exit

The longitudinal momentum of the electron at the tunneling exit is a useful quantity to make sense of the tunneling ionization process. It was usually assumed to be zero from a classical argument, but recent experiments show that it must be nonzero in order to explain the measured electron momentum distributions. In this article we show that the flow momentum of the probability fluid is a sensible quantum mechanical definition for tunneling-exit momentum, and it can be (and in general is) nonzero at the tunneling exit point where the kinetic energy is zero by definition. We show that this longitudinal momentum is nonzero even in the static or adiabatic limit, and this nonzero momentum is a purely quantum mechanical effect determined by the shape of the wave function in the vicinity of the tunneling exit point. Nonadiabaticity or finite wavelength may increase this momentum substantially, and the detailed value depends on both the atomic and the laser parameters.

physics.atom-ph↗
arXiv2018

Music Sequence Prediction with Mixture Hidden Markov Models

Recommendation systems that automatically generate personalized music playlists for users have attracted tremendous attention in recent years. Nowadays, most music recommendation systems rely on item-based or user-based collaborative filtering or content-based approaches. In this paper, we propose a novel mixture hidden Markov model (HMM) for music play sequence prediction. We compare the mixture model with state-of-the-art methods and evaluate the predictions quantitatively and qualitatively on a large-scale real-world dataset in a Kaggle competition. Results show that our model significantly outperforms traditional methods as well as other competitors. We conclude by envisioning a next-generation music recommendation system that integrates our model with recent advances in deep learning, computer vision, and speech techniques, and has promising potential in both academia and industry.

cs.IR↗
arXiv2018

HashTran-DNN: A Framework for Enhancing Robustness of Deep Neural Networks against Adversarial Malware Samples

Adversarial machine learning in the context of image processing and related applications has received a large amount of attention. However, adversarial machine learning, especially adversarial deep learning, in the context of malware detection has received much less attention despite its apparent importance. In this paper, we present a framework for enhancing the robustness of Deep Neural Networks (DNNs) against adversarial malware samples, dubbed Hashing Transformation Deep Neural Networks} (HashTran-DNN). The core idea is to use hash functions with a certain locality-preserving property to transform samples to enhance the robustness of DNNs in malware classification. The framework further uses a Denoising Auto-Encoder (DAE) regularizer to reconstruct the hash representations of samples, making the resulting DNN classifiers capable of attaining the locality information in the latent space. We experiment with two concrete instantiations of the HashTran-DNN framework to classify Android malware. Experimental results show that four known attacks can render standard DNNs useless in classifying Android malware, that known defenses can at most defend three of the four attacks, and that HashTran-DNN can effectively defend against all of the four attacks.

cs.CR↗
arXiv2018

Variation of Contact Resonance Frequency during Domain Switching in PFM Measurements for Ferroelectric Materials

Piezoresponse Force Spectroscopy (PFS) is a powerful method widely used for measuring the nanoscale ferroelectric responses of the materials. However, it is found that certain non-ferroelectric materials can also generate similar responses from the PFS measurements due to many other factors, hence, it is believed that PFS alone is not sufficient to differentiate the ferroelectric and non-ferroelectric materials. On the other hands, this work shows that there are distinct differences in contact resonance frequency variation during the PFS measurements for ferroelectric and non-ferroelectric materials. Therefore, a new, simple and effective method is proposed to differentiate the responses from the ferroelectric and non-ferroelectric materials, this new analysis uses contact resonance frequency responses during the PFS measurements as a new parameter to differentiate the PFS measured responses from different materials.

cond-mat.mtrl-sci↗
arXiv2018

Entanglement purification of nonlocal quantum-dot-confined electrons assisted by double-sided optical microcavities

We present a nondestructive parity-check detector (PCD) scheme for two single-electron quantum dots embedded in double-sided optical microcavities. Using a polarization-entangled photon pair, the PCD works in a parallel style and is robust to the phase fluctuation of the optical path length. In addition, we present an economic entanglement purification protocol for electron pairs with our nondestructive PCD. The parties in quantum communication can increase the purification efficiency and simultaneously decrease the quantum source consumed for some particular fidelity thresholds. Therefore, our protocol has good applications in the future quantum communication and distributed quantum networks.

quant-ph↗
arXiv2018

Self-error-rejecting quantum state transmission of entangled photons for faithful quantum communication without calibrate reference frames

We propose an alignment-free two-party polarization-entanglement transmission scheme for entangled photons by using only linear-optical elements, requiring neither ancillary photons nor calibrated reference frames. The scheme is robust against both the random channel noise and the instability of reference frames, and it is subsequently extended to multi-party Greenberger-Horne-Zeilinger state transmission. Furthermore, the success probabilities for two- and multi-party entanglement transmission are, in principle, improved to unity when active polarization controllers are used. The distinct characters of a simple structure, easy to be implemented, and a high fidelity and efficiency make our protocol very useful for long-distance quantum communications and distributed quantum networks in practical applications.

quant-ph↗
arXiv2018

Self-error-corrected hyperparallel photonic quantum computation working with both the polarization and the spatial-mode degrees of freedom

Usually, the hyperparallel quantum computation can speed up quantum computing, reduce the quantum resource consumed largely, resist to noise, and simplify the storage of quantum information. Here, we present the first scheme for the self-error-corrected hyperparallel photonic quantum computation working with both the polarization and the spatial-mode degrees of freedom of photon systems simultaneously. It can prevent bit-flip errors from happening with an imperfect nonlinear interaction in the nearly realistic condition. We give the way to design the universal hyperparallel photonic quantum controlled-NOT (CNOT) gate on a two-photon system, resorting to the nonlinear interaction between the circularly polarized photon and the electron spin in the quantum dot in a double-sided microcavity system, by taking the imperfect interaction in the nearly realistic condition into account. Its self-error-corrected pattern prevents the bit-flip errors from happening in the hyperparallel quantum CNOT gate, guarantees the robust fidelity, and relaxes the requirement for its experiment. Meanwhile, this scheme works in a failure-heralded way. Also, we generalize this approach to achieve the self-error-corrected hyperparallel quantum CNOT$^N$ gate working on a multiple-photon system. These good features make this scheme more useful in the photonic quantum computation and quantum communication in the future.

quant-ph↗
arXiv2018

Observation of anomalous π modes in photonic Floquet engineering

Recent progresses on Floquet topological phases have shed new light on time-dependant quantum systems, among which one-dimensional (1D) Floquet systems have been under extensive theoretical research. However, an unambiguous experimental observation of these 1D Floquet topological phases has still been lacking. Here, by periodically bending ultrathin metallic arrays of coupled corrugated waveguides, a photonic Floquet simulator was well designed and successfully fabricated to simulate the periodically driven Su-Schrieffer-Heeger model. Intriguingly, under moderate driven frequencies, we first experimentally observed and theoretically verified the Floquet topological $π$ mode propagating along the array's boundary. The different evolutionary behaviors between static and non-static topological end modes have also been clearly demonstrated. Our experiment also reveals the universal high-frequency behavior in perically driven systems. We emphasize that, our system can serve as a powerful and versatile testing ground for various phenomena related to time-dependant 1D quantum phases, such as Thouless charge pumping and manybody localization.

quant-ph↗
arXiv2018

Vanishing pseudogap around $(π,0)$ in an electron-doped high-$\mathrm{T_{c}}$ superconductor: a simple picture

Recent ARPES measurement on electron-doped cuprate $\mathrm{Pr}_{1.3-x}\mathrm{La}_{0.7}\mathrm{Ce}_{x}\mathrm{CuO}_{4}$ finds that the pseudogap along the boundary of the antiferromagnetic Brillouin zone(AFBZ) exhibits dramatic momentum dependence. In particular, the pseudogap vanishes in a finite region around the anti-nodal point, in which a single broadened peak emerges at the un-renormalized quasiparticle energy. Such an observation is argued to be inconsistent with the antiferromagnetic(AFM) band-folding picture, which predicts a constant pseudogap along the AFBZ boundary. On the other hand, it is claimed that the experimental results are consistent with the prediction of the cluster dynamical mean field theory(CDMFT) simulation on the Hubbard model, in which the pseudogap is interpreted as a s-wave splitting between the Hubbard bands and the in-gap states. Here we show that the observed momentum dependence of the pseudogap is indeed consistent with AFM band-folding picture, provided that we assume the existence of a strongly momentum dependent quasiparticle scattering rate. More specifically, we show that the quasiparticle scattering rate acts to reduce the spectral gap induced by AFM band-folding effect. The new quasiparticle poles corresponding to the AF-split bands can even be totally eliminated when the scattering rate exceeds the bare band folding gap, leaving the system with a single pole at the un-renormalized quasiparticle energy. We predict that the pseudogap should close in a square root fashion as we move toward $(π,0)$ along the AFBZ boundary. Our results illustrates again that the quasiparticle scattering rate can play a much more profound role than simply broadening the quasiparticle peak in the quasiparticle dynamics of strongly correlated electron systems.

cond-mat.str-el↗
arXiv2018

Cooperative Adaptive Cruise Control for a Platoon of Connected and Autonomous Vehicles Considering Dynamic Information Flow Topology

Vehicle-to-vehicle communications can be unreliable as interference causes communication failures. Thereby, the information flow topology for a platoon of Connected Autonomous Vehicles (CAVs) can vary dynamically. This limits existing Cooperative Adaptive Cruise Control (CACC) strategies as most of them assume a fixed information flow topology (IFT). To address this problem, we introduce a CACC design that considers a dynamic information flow topology (CACC-DIFT) for CAV platoons. An adaptive Proportional-Derivative (PD) controller under a two-predecessor-following IFT is proposed to reduce the negative effects when communication failures occur. The PD controller parameters are determined to ensure the string stability of the platoon. Further, the designed controller also factors the performance of individual vehicles. Hence, when communication failure occurs, the system will switch to a certain type of CACC instead of degenerating to adaptive cruise control, which improves the control performance considerably. The effectiveness of the proposed CACC-DIFT is validated through numerical experiments based on NGSIM field data. Results indicate that the proposed CACC-DIFT design outperforms a CACC with a predetermined information flow topology.

eess.SY↗
arXiv2018

Cooperative Adaptive Cruise Control for Connected Autonomous Vehicles by Factoring Communication-Related Constraints

Emergent cooperative adaptive cruise control (CACC) strategies being proposed in the literature for platoon formation in the Connected Autonomous Vehicle (CAV) context mostly assume idealized fixed information flow topologies (IFTs) for the platoon, implying guaranteed vehicle-to-vehicle (V2V) communications for the IFT assumed. Since CACC strategies entail continuous information broadcasting, communication failures can occur in congested CAV traffic networks, leading to a platoon's IFT varying dynamically. To enhance the performance of CACC strategies, this study proposes the idea of dynamically optimizing the IFT for CACC, labeled the CACC-OIFT strategy. Under CACC-OIFT, the vehicles in the platoon cooperatively determine in real-time which vehicles will dynamically deactivate or activate the "send" functionality of their V2V communication devices to generate IFTs that optimize the platoon performance in terms of string stability under the ambient traffic conditions. Given the adaptive Proportional-Derivative (PD) controller with a two-predecessor-following scheme, and the ambient traffic conditions and the platoon size just before the start of a time period, the IFT optimization model determines the optimal IFT that maximizes the expected string stability. The optimal IFT is deployed for that time period, and the adaptive PD controller continuously determines the car-following behaviors of the vehicles based on the unfolding degeneration scenario for each time instant within that period. The effectiveness of the proposed CACC-OIFT is validated through numerical experiments in NS-3 based on NGSIM field data. The results indicate that the proposed CACC-OIFT can significantly enhance the string stability of platoon control in an unreliable V2V communication context, outperforming CACCs with fixed IFTs or with passive adaptive schemes for IFT dynamics.

eess.SY↗
arXiv2018

$Z_{2}$ spin liquid ground state of the spin-$\frac{1}{2}$ Kagome antiferromagnetic Heisenberg model

We show that the best variational ground state of the spin-$\frac{1}{2}$ Kagome antiferromagnetic Heisenberg model with nearest-neighboring exchange coupling(NN-KAFH) is a $Z_{2}$ spin liquid state, rather than the widely believed $U(1)$ Dirac spin liquid state. The spinon excitation in the $Z_{2}$ spin liquid state has a small gap of about $1/40$ of the spinon band width. We find that while the $Z_{2}$ and the $U(1)$ spin liquid state have a large overlap on finite clusters and are thus very close in energy, they host totally different spinon excitation spectrum. The strength of the RVB theory becomes particularly clear in such a situation, as it provides not only a variational understanding of the ground state structure, but also a comprehensive picture for the excitation spectrum of the system. Our result indicates that the spin-$\frac{1}{2}$ NN-KAFH should be better understood as a nearly critical system, rather than a prototypical gapped $Z_{2}$ spin liquid system.

cond-mat.str-el↗
arXiv2018

Topological solid phase in a quantum dimer model

We present an example for the phase transition between a topological non-trivial solid phase and a trivial solid phase in the quantum dimer model(QDM) on triangular lattice. Such a transition is beyond the Landau's paradigm of phase transition. We have characterized such a transition with the topological entanglement entropy(TEE) of the system, which is found to change from $γ=\ln 2$ in the topological solid phase to zero in the trivial solid phase, through a pronounced peak around the transition point. We also calculated the correlation function of the vison excitation in the QDM and find that the vison condensate develops right at the topological transition point. These results imply that the topological order and the related fractionalized excitation can coexist with conventional symmetry breaking order.

cond-mat.str-el↗
arXiv2018

The driving mechanism of the d-wave orbital order in the iron-based superconductors

We study the driving mechanism and the form of the orbital order in the electronic nematic phase of the iron-based superconductors(IBSs) within the random phase approximation of a 5-band model. We find the magnetic correlation energy of the system can be significantly improved when an orbital order of the d-wave form is spontaneously generated. On the other hand, the magnetic correlation energy increases as one introduce either an on-site or an extended s-wave orbital order. More specifically, we find that the on-site orbital order is disfavored by the Hund's rule coupling and the extended s-wave orbital order is disfavored by the stripy magnetic correlation pattern in the IBSs.

cond-mat.supr-con↗
arXiv2018

Quantum memory and gates using a Lambda-type quantum emitter coupled to a chiral waveguide

By coupling a $Λ$-type quantum emitter to a chiral waveguide, in which the polarization of a photon is locked to its propagation direction, we propose a controllable photon-emitter interface for quantum networks. We show that this chiral system enables the SWAP gate and a hybrid-entangling gate between the emitter and a flying single photon. It also allows deterministic storage and retrieval of single-photon states with high fidelities and efficiencies. In short, this chirally coupled emitter-photon interface can be a critical building block toward a large-scale quantum network.

quant-ph↗