arXiv subjects

Yu Zhou

Publications and source records attributed to Yu Zhou.

At least 415 records · Page 23Linked to original sources

arXiv2018

Bright room temperature single photon source at telecom range in cubic silicon carbide

Single photon emitters (SPEs) play an important role in a number of quantum information tasks such as quantum key distributions. In these protocols, telecom wavelength photons are desired due to their low transmission loss in optical fibers. In this paper, we present a study of bright single-photon emitters in cubic silicon carbide (3C-SiC) emitting in the telecom range. We find that these emitters are photostable and bright at room temperature with a count rate of ~ MHz. Together with the fact that SiC is a growth and fabrication-friendly material, our result may pave the way for its future application in quantum communication technology applications.

physics.optics↗

arXiv2018

Experimental observation of three-photon superbunching in linear optical system

Three-photon superbunching is experimentally observed with the recently proposed superbunching pseudothermal light. To the best of our knowledge, it is the first time that three-photon superbunching is observed in linear optical system. From the quantum optics point of view, three-photon superbunching is interpreted as the result of constructive-destructive three-photon interference. The key to observe three-photon superbunching in superbunching pseudothermal light is that all the different ways to trigger a three-photon coincidence count are in principle indistinguishable, which is experimentally guaranteed by putting a pinhole before each rotating groundglass to ensure that all the passed photons are within one coherence area. The observed three-photon superbunching is helpful to increase the visibility of ghost imaging and understand the physics of third-order interference of light.

quant-ph↗

arXiv2018

Superbunching pseudothermal light with intensity modulated laser light and rotating groundglass

Pseudothermal light by scattering laser light from rotating groundglass has been extensively employed to study optical coherence in both classical and quantum optics ever since its invention in 1960s. In this paper, we will show that by replacing the invariant intensity laser light in pseudothermal light source with intensity modulated laser light, superbunching pseudothermal light can be obtained. Two-photon interference in Feynman's path integral theory is employed to interpret the phenomenon. Two-photon superbunching is experimentally observed by employing common instruments in optical laboratory. The proposed superbunching pseudothermal light is helpful to understand the physics of two-photon bunching and superbunching, and the difference between classical and quantum interpretations of the second- and higher-order interference of light.

quant-ph↗

arXiv2018

Source-Critical Reinforcement Learning for Transferring Spoken Language Understanding to a New Language

To deploy a spoken language understanding (SLU) model to a new language, language transferring is desired to avoid the trouble of acquiring and labeling a new big SLU corpus. Translating the original SLU corpus into the target language is an attractive strategy. However, SLU corpora consist of plenty of semantic labels (slots), which general-purpose translators cannot handle well, not to mention additional culture differences. This paper focuses on the language transferring task given a tiny in-domain parallel SLU corpus. The in-domain parallel corpus can be used as the first adaptation on the general translator. But more importantly, we show how to use reinforcement learning (RL) to further finetune the adapted translator, where translated sentences with more proper slot tags receive higher rewards. We evaluate our approach on Chinese to English language transferring for SLU systems. The experimental results show that the generated English SLU corpus via adaptation and reinforcement learning gives us over 97% in the slot F1 score and over 84% accuracy in domain classification. It demonstrates the effectiveness of the proposed language transferring method. Compared with naive translation, our proposed method improves domain classification accuracy by relatively 22%, and the slot filling F1 score by relatively more than 71%.

cs.CL↗

arXiv2018

Highly-efficient spintronic terahertz emitter enabled by metal-dielectric photonic crystal

Spintronic terahertz (THz) emitter provides the advantages such as apparently broader spectrum, significantly lower cost, and more flexibility in compared with the commercial THz emitters, and thus attracts great interests recently. In past few years, efforts have been made in optimizing the material composition and structure geometry, and the conversion efficiency has been improved close to that of ZnTe crystal. One of the drawbacks of the current designs is the rather limited laser absorption - more than 50% energy is wasted and the conversion efficiency is thus limited. Here, we theoretically propose and experimentally demonstrate a novel device that fully utilizes the laser intensity and significantly improves the conversion efficiency. The device, which consists of a metal-dielectric photonic crystal structure, utilizes the interference between the multiple scattering waves to simultaneously suppress the reflection and transmission of the laser, and to reshape the laser field distributions. The experimentally detected laser absorption and THz generations show one-to-one correspondence with the theoretical calculations. We achieve the strongest THz pulse emission that presents a 1.7 times improvement compared to the currently designed spintronic emitter. This work opens a new pathway to improve the performance of spintronic THz emitter from the perspective of optics.

cond-mat.mes-hall↗

arXiv2018

Recurrent Meta-Structure for Robust Similarity Measure in Heterogeneous Information Networks

Similarity measure as a fundamental task in heterogeneous information network analysis has been applied to many areas, e.g., product recommendation, clustering and Web search. Most of the existing metrics depend on the meta-path or meta-structure specified by users in advance. These metrics are thus sensitive to the pre-specified meta-path or meta-structure. In this paper, a novel similarity measure in heterogeneous information networks, called Recurrent Meta-Structure-based Similarity (RMSS), is proposed. The recurrent meta-structure as a schematic structure in heterogeneous information networks provides a unified framework to integrate all of the meta-paths and meta-structures. Therefore, RMSS is robust to the meta-paths and meta-structures. We devise an approach to automatically constructing the recurrent meta-structure. In order to formalize the semantics, the recurrent meta-structure is decomposed into several recurrent meta-paths and recurrent meta-trees, and we then define the commuting matrices of the recurrent meta-paths and meta-trees. All of the commuting matrices of the recurrent meta-paths and meta-trees are combined according to different weights. Note that the weights can be determined by two kinds of weighting strategies: local weighting strategy and global weighting strategy. As a result, RMSS is defined by virtue of the final commuting matrix. Experimental evaluations show that the existing metrics are sensitive to different meta-paths or meta-structures and that the proposed RMSS outperforms the existing metrics in terms of ranking and clustering tasks.

cs.DB↗

arXiv2018

Derived equivalences via HRS-tilting

Let $\mathcal{A}$ be an abelian category and $\mathcal{B}$ be the Happel-Reiten-Smalø tilt of $\mathcal{A}$ with respect to a torsion pair. We give necessary and sufficient conditions for the existence of a derived equivalence between $\mathcal{B}$ and $\mathcal{A}$, which is compatible with the inclusion of $\mathcal{B}$ into the derived category of $\mathcal{A}$. In particular, any splitting torsion pair induces a derived equivalence. We prove that for the realization functor of any bounded $t$-structure, its denseness implies its fully-faithfulness.

math.RT↗

arXiv2018

Decorated marked surfaces III: The derived category of a decorated marked surface

We study the Ginzburg dg algebra $Γ_\mathbf{T}$ associated to the quiver with potential arising from a triangulation $\mathbf{T}$ of a decorated marked surface $\mathbf{S}_\bigtriangleup$, in the sense of Qiu. We show that there is a canonical way to identify all finite dimensional derived categories $\mathcal{D}_{fd}(Γ_\mathbf{T})$, denoted by $\mathcal{D}_{fd}(\mathbf{S}_\bigtriangleup)$. As an application, we show that the spherical twist group $\operatorname{ST}(\mathbf{S}_\bigtriangleup)$ associated to $\mathcal{D}_{fd}(\mathbf{S}_\bigtriangleup)$ acts faithfully on its space of stability conditions.

math.RT↗

arXiv2018

Molecular Communications at the Macroscale: A Novel Framework for Modeling Epidemic Spreading and Mitigation

Using the notion of effective distance proposed by Brockmann and Helbing, complex spatiotemporal processes of epidemic spreading can be reduced to circular wave propagation patterns with well-defined wavefronts. This hidden homogeneity of contagion phenomena enables the mapping of virtual mobility networks to physical propagation channels. Subsequently, we propose a novel communications-inspired model of epidemic spreading and mitigation by establishing the one-to-one correspondence between the essential components comprising information and disease transmissions. The epidemic processes can be regarded as macroscale molecular communications, in which individuals are macroscale information molecules carrying messages (epidemiological states). We then present the notions of normalized ensemble-average prevalence (NEAP) and prevalence delay profile (PDP) to characterize the relative impact and time difference of all the spreading paths, which are analogous to the classical description methods of path loss and power delay profile in communications. Furthermore, we introduce the metric of root mean square (RMS) delay spread to measure the distortion of early contagion dynamics caused by multiple infection transmission routes. In addition, we show how social and medical interventions can be understood from the perspectives of various communication modules. The proposed framework provides an intuitive, coherent, and efficient approach for characterization of the disease outbreaks by applying the deep-rooted communications theories as the analytical lens.

physics.soc-ph↗

arXiv2018

Jet mixing optimization using machine learning control

We experimentally optimize mixing of a turbulent round jet using machine learning control (MLC) following Li et al (2017). The jet is manipulated with one unsteady minijet blowing in wall-normal direction close to the nozzle exit. The flow is monitored with two hotwire sensors. The first sensor is positioned on the centerline 5 jet diameters downstream of the nozzle exit, i.e. the end of the potential core, while the second is located 3 jet diameters downstream and displaced towards the shear-layer. The mixing performance is monitored with mean velocity at the first sensor. A reduction of this velocity correlates with increased entrainment near the potential core. Machine Learning Control (MLC) is employed to optimize sensor feedback, a general open-loop broadband frequency actuation and combinations of both. MLC has identified the optimal periodic forcing with a small duty cycle as the best control policy employing only 400 actuation measurements, each lasting for 5 seconds. This learning rate is comparable if not faster than typical optimization of periodic forcing with two free parameters (frequency and duty cycle). In addition, MLC results indicate that neither new frequencies nor sensor feedback improves mixing further-contrary to many of other turbulence control experiments. The optimality of pure periodic actuation may be attributed to the simple jet flapping mechanism in the minijet plane. The performance of sensor feedback is shown to face a challenge for small duty cycles. The jet mixing results demonstrate the untapped potential of MLC in quickly learning optimal general control policies, even deciding between open- and closed-loop control.

physics.flu-dyn↗

arXiv2018

A Semantic-Rich Similarity Measure in Heterogeneous Information Networks

Measuring the similarities between objects in information networks has fundamental importance in recommendation systems, clustering and web search. The existing metrics depend on the meta path or meta structure specified by users. In this paper, we propose a stratified meta structure based similarity $SMSS$ in heterogeneous information networks. The stratified meta structure can be constructed automatically and capture rich semantics. Then, we define the commuting matrix of the stratified meta structure by virtue of the commuting matrices of meta paths and meta structures. As a result, $SMSS$ is defined by virtue of these commuting matrices. Experimental evaluations show that the proposed $SMSS$ on the whole outperforms the state-of-the-art metrics in terms of ranking and clustering.

cs.DB↗

arXiv2018

Tunable multiband directional electromagnetic scattering from spoof Mie resonant structure

We demonstrate that directional electromagnetic scattering can be realized from a artificial Mie resonant strcuture which supports electric and magnetic dipole modes simultaneously. The directivity of the far-field radiation pattern can be switched by changing the incident light wavelength as well as tailoring the geometric parameters of the structure. Particularly, the electric quadrupole at higher frequency contribute significantly to the scattered fields, leading to enhancement of the directionality. In addition, we further design a quasiperiodic spoof Mie resonant structure by alternately inserting two materials into the slits. The results show that multi-band directional light scattering are realized by exciting multiple electric and magnetic dipole modes with different frequencies in the quasiperiodic structure. The presented design concept is general from microwave to terahertz region and can be applied for various advanced optical devices, such as antenna, metamaterial and metsurface.

physics.optics↗

arXiv2017

Profitability of simple stationary technical trading rules with high-frequency data of Chinese Index Futures

Technical trading rules have been widely used by practitioners in financial markets for a long time. The profitability remains controversial and few consider the stationarity of technical indicators used in trading rules. We convert MA, KDJ and Bollinger bands into stationary processes and investigate the profitability of these trading rules by using 3 high-frequency data(15s,30s and 60s) of CSI300 Stock Index Futures from January 4th 2012 to December 31st 2016. Several performance and risk measures are adopted to assess the practical value of all trading rules directly while ADF-test is used to verify the stationarity and SPA test to check whether trading rules perform well due to intrinsic superiority or pure luck. The results show that there are several significant combinations of parameters for each indicator when transaction costs are not taken into consideration. Once transaction costs are included, trading profits will be eliminated completely. We also propose a method to reduce the risk of technical trading rules.

q-fin.ST↗

arXiv2017

Out-of-plane Piezoelectricity and Ferroelectricity in Layered $α$-In2Se3 Nano-flakes

Piezoelectric and ferroelectric properties in the two dimensional (2D) limit are highly desired for nanoelectronic, electromechanical, and optoelectronic applications. Here we report the first experimental evidence of out-of-plane piezoelectricity and ferroelectricity in van der Waals layered $α$-In2Se3 nano-flakes. The non-centrosymmetric R3m symmetry of the $α$-In2Se3 samples is confirmed by scanning transmission electron microscopy, second-harmonic generation, and Raman spectroscopy measurements. Domains with opposite polarizations are visualized by piezo-response force microscopy. Single-point poling experiments suggest that the polarization is potentially switchable for $α$-In2Se3 nano-flakes with thicknesses down to ~ 10 nm. The piezotronic effect is demonstrated in two-terminal devices, where the Schottky barrier can be modulated by the strain-induced piezopotential. Our work on polar $α$-In2Se3, one of the model 2D piezoelectrics and ferroelectrics with simple crystal structures, shows its great potential in electronic and photonic applications.

cond-mat.mtrl-sci↗

arXiv2017

Room-temperature solid state quantum emitters in the telecom range

On demand single photon emitters (SPEs) play a key role across a broad range of quantum technologies, including quantum computation, quantum simulation, quantum metrology and quantum communications. In quantum networks and quantum key distribution protocols, where photons are employed as flying qubits, telecom wavelength operation is preferred due to the reduced fibre loss. However, despite the tremendous efforts to develop various triggered SPE platforms, a robust source of triggered SPEs operating at room temperature and the telecom wavelength is still missing. Here we report a triggered, optically stable, room temperature solid state SPE operating at telecom wavelengths. The emitters exhibit high photon purity (~ 5% multiphoton events) and a record-high brightness of ~ 1.5 MHz. The emission is attributed to localized defects in a gallium nitride (GaN) crystal. The high performance SPEs embedded in a technologically mature semiconductor are promising for on-chip quantum simulators and practical quantum communication technologies.

quant-ph↗

arXiv2017

High visibility temporal ghost imaging with classical light

High visibility temporal ghost imaging with classical light is possible when superbunching pseudothermal light is employed. In the numerical simulation, the visibility of temporal ghost imaging with pseudothermal light equaling ($4.7\pm 0.2$)\% can be increased to ($75\pm 8$)\% in the same scheme with superbunching pseudothermal light. The reasons for the difference in visibility and quality of the retrieved images in different situations are discussed in detail. It is concluded that high visibility and high quality temporal ghost image can be obtained by collecting large enough number of data points. The results are helpful to understand the difference between ghost imaging with classical light and entangled photon pairs. The superbunching pseudothermal light can be employed to improve the image quality in ghost imaging applications.

quant-ph↗

arXiv2017

Mutation of torsion pairs in triangulated categories and its geometric realization

We introduce and study mutation of torsion pairs, as a generalization of mutation of cluster tilting objects, rigid objects and maximal rigid objects. It is proved that any mutation of a torsion pair is again a torsion pair. A geometric realization of mutation of torsion pairs in the cluster category of type $A_n$ or $A_{\infty}$ is given via rotation of Ptolemy diagrams.

math.RT↗

arXiv2017

Decorated marked surfaces II: Intersection numbers and dimensions of Homs

We study the 3-Calabi-Yau categories $\mathcal{D}$ arising from quivers with potential associated to a decorated marked surface $\mathbf{S}_\bigtriangleup$ introduced by the first author. We prove two conjectures in the prequel, that under a bijection between certain objects in $\mathcal{D}$ and certain arcs in $\mathbf{S}_\bigtriangleup$, the dimensions of morphisms between these objects equal the intersection numbers between the corresponding arcs.

math.RT↗