arXiv subjects

Chen Liu

Publications and source records attributed to Chen Liu.

283 records · Page 16Linked to original sources

arXiv2015

Non-Markovian effect on remote state preparation

Memory effect of non-Markovian dynamics in open quantum systems is often believed to be beneficial for quantum information processing. In this work, we employ an experimentally controllable two-photon open system, with one photon experiencing a dephasing environment and the other being free from noise, to show that non-Markovian effect may also have a negative impact on quantum tasks such as remote state preparation: For a certain period of controlled time interval, stronger non-Markovian effect yields lower fidelity of remote state preparation, as opposed to the common wisdom that more information leads to better performance. As a comparison, a positive non-Markovian effect on the RSP fidelity with another typical non-Markovian noise is analyzed. Consequently, the observed dual character of non-Markovian effect will be of great importance in the field of open systems engineering.

quant-ph↗

arXiv2015

Quantum-speed-limit time for multiqubit open systems

Quantum-speed-limit (QSL) time captures the intrinsic minimal time interval for a quantum system evolving from an initial state to a target state. In single qubit open systems, it was found that the memory (non-Markovian) effect of environment plays an essential role in shortening QSL time or, say, increasing the capacity for potential speedup. In this paper, we investigate the QSL time for multiqubit open systems. We find that for a certain class of states the memory effect still acts as the indispensable requirement for cutting the QSL time down, while for another class of states this takes place even when the environment is of no memory. In particular, when the initial state is in product state |111...1>, there exists a sudden transition from no capacity for potential speedup to potential speedup in a memoryless environment. In addition, we also display evidence for the subtle connection between QSL time and entanglement that weak entanglement may shorten QSL time even more.

quant-ph↗

arXiv2014

Effects of Oxygen Adsorption on the Surface State of Epitaxial Silicene on Ag(111)

Epitaxial silicene, which is one single layer of silicon atoms packed in a honeycomb structure, demonstrates a strong interaction with the substrate that dramatically affects its electronic structure. The role of electronic coupling in the chemical reactivity between the silicene and the substrate is still unclear so far, which is of great importance for functionalization of silicene layers. Here, we report the reconstructions and hybridized electronic structures of epitaxial 4x4 silicene on Ag(111), which are revealed by scanning tunneling microscopy and angle-resolved photoemission spectroscopy. The hybridization between Si and Ag results in a metallic surface state, which can gradually decay due to oxygen adsorption. X-ray photoemission spectroscopy confirms the decoupling of Si-Ag bonds after oxygen treatment as well as the relatively oxygen resistance of Ag(111) surface, in contrast to 4x4 silicene [with respect to Ag(111)]. First-principles calculations have confirmed the evolution of the electronic structure of silicene during oxidation. It has been verified experimentally and theoretically that the high chemical activity of 4x4 silicene is attributable to the Si pz state, while the Ag(111) substrate exhibits relatively inert chemical behavior.

cond-mat.mes-hall↗

arXiv2014

Plasmonic lasing of nanocavity embedding in metallic nanoantenna array

Plasmonic nanolasers have ultrahigh lasing thresholds, especially those devices for which all three dimensions are truly subwavelength. Because of a momentum mismatch between the propagating light and localized optical field of the subwavelength nanocavity, poor optical pumping efficiency is another important reason for the ultrahigh threshold but is normally always ignored. Based on a cavity-embedded nanoantenna array design, we demonstrate a room-temperature low-threshold plasmonic nanolaser that is robust, reproducible, and easy-to-fabricate using chemical-template lithography. The mode volume of the device is~0.22(λ/2n)3 (here,λ is resonant wavelength and n is the refractive index), and the experimental lasing threshold produced is ~2.70MW/mm2. The lasing polarization and the function of nanoantenna array are investigated in detail. Our work provides a new strategy to achieve room-temperature low-threshold plasmonic nanolasers of interest in applications to biological sensoring and information technology.

physics.optics↗

arXiv2014

Tracing The Largest Seasonal Migration on Earth

It is estimated that over 3.6 billion passengers are travelling during the Chinese Spring Festival travel season. They leave their working cities and return their hometowns to enjoy annual family time, and back to cities after the holiday. In this study, with the massive location-based data collected from millions of smartphone users, we propose a novel method to trace the migration flow and explore the migration patterns of Chinese people. From the temporal perspective, we explore the migration trend over time during a 34-days period, about half a month before and after the Spring Festival. From the spatial perspective, the migration directions and routes are estimated and quantified, and the migration flow is visualized. The spatial range of influence of developed regions could be reflected with the destinations of migration, the migration destinations and originations have obvious characteristic of geographical proximity.

physics.soc-ph↗

arXiv2014

Does A Paper Being Featured on The Cover of A Journal Guarantee More Attention and Greater Impact?

Paper featured on the cover of a journal has more visibility in an issue compared with other ordinary articles for both printed and electronic journal. Does this kind of visibility guarantee more attention and greater impact of its associated content than the non-cover papers? In this research, usage and citation data of 60 issues of PLOS Biology from 2006 to 2010 are analyzed to compare the attention and scholarly impact between cover and non-cover paper. Our empirical study confirms that, in most cases, the group difference between cover and non-cover paper is not significant for attention or impact. Cover paper is not the best one, nor at the upper level in one issue considering the attention or the citation impact. Having a paper featured on the cover of a journal may be a source of pride to researchers, many institutions and researchers would even release news about it. However, a paper being featured on the cover of a journal doesn't guarantee more attention and greater impact.

cs.DL↗

arXiv2014

From Attention to Citation, What and How Does Altmetrics Work?

Scholarly and social impacts of scientific publications could be measured by various metrics. In this study, the relationship between various metrics of 63,805 PLOS research articles are studied. Generally, article views correlate well with citation, however, different types of article view have different levels of correlation with citation, when pdf download correlates the citation most significantly. It's necessary for publishers and journals to provide detailed and comprehensive article metrics. Although the low correlation between social attention and citation is confirmed by this study and previous studies, more than ever, we find that social attention is highly correlated with article view, especially the browser html view. Social attention is the important source that bringing network traffic to browser html view and may lead to citation subsequently. High altmetric score has the potential role in promoting the long-term academic impact of articles, when a conceptual model is proposed to interpret the conversion from social attention to article view, and to citation finally.

cs.DL↗

arXiv2014

How far does scientific community look back?

How does the published scientific literature used by scientific community? Many previous studies make analysis on the static usage data. In this research, we propose the concept of dynamic usage data. Based on the platform of realtime.springer.com, we have been monitoring and recording the dynamic usage data of Scientometrics articles round the clock. Our analysis find that papers published in recent four years have many more downloads than papers published four years ago. According to our quantitative calculation, papers down-loaded on one day have an average lifetime of 4.1 years approximately. Classic papers are still being downloaded frequently even long after their publication. Additionally, we find that social media may reboot the attention of old scientific literature in a short time.

cs.DL↗

arXiv2014

Quantum speedup in a memory environment

Memory (non-Markovian) effect is found to be able to accelerate quantum evolution [S. Deffner and E. Lutz, Phys. Rev. Lett. 111, 010402 (2013)]. In this work, for an atom in a structured reservoir, we show that the mechanism for the speedup is not only related to non-Markovianity but also to the population of excited states under a given driving time. In other words, it is the competition between non-Markovianity and population of excited states that ultimately determines the acceleration of quantum evolution in memory environment. A potential experimental realization for verifying the above phenomena is discussed by using a nitrogen-vacancy (N-V) center embedded in a planar photonic crystal cavity (PCC) under the current experimental conditions.

quant-ph↗

arXiv2013

Finite-temperature decoherence of spin states in a $\texttt{\{}\emph{Cu}_3\texttt{\}}$ single molecular magnet

We investigate the quantum evolution of spin states of a single molecular magnet in a local electric field. The decoherence of a $\texttt{\{}\emph{Cu}_3\texttt{\}}$ single molecular magnet weakly coupled to a thermal bosonic environment can be analyzed by the spin-boson model. Using the finite-temperature time-convolutionless quantum master equation, we obtain the analytical expression of the reduced density matrix of the system in the secular approximation. The suppressed and revived dynamical behavior of the spin states are presented by the oscillation of the chirality spin polarization on the time scale of the correlation time of the environment. The quantum decoherence can be effectively restrained with the help of the manipulation of local electric field and the environment spectral density function. Under the influence of the dissipation, the pointer states measured by the von Neumann entropy are calculated to manifest the entanglement property of the system-environment model.

quant-ph↗

arXiv2013

Games and Culture: Using Online-gaming Data to Cluster Chinese Regional Cultures

To identify cluster of societies and cultures is not easy in subject to the availability of data. In this study, we propose a novel method to cluster Chinese regional cultures. Using geotagged online-gaming data of Chinese internet users playing online card and board games with regional features, 336 Chinese cities are grouped into 17 clusters. The distribution of clustering units shows great geographical proximity when the boundary of the clusters coincides well with the geographical boundary of provinces.

cs.CY↗

arXiv2012

Quantum decoherence of spin states in an electric-field controllable single molecular magnet

The time evolution of low energy spin states of a single molecular magnet in a local electric field is investigated. The decoherence of the driven single molecular magnet weakly coupled to a thermal bosonic environment is analyzed by the second-order time-convolutionless non-Markovian master equation. If the characteristic time of the system is much smaller than the correlation time of the environment, the analytical expression of the reduced density matrix of the system is obtained. The non-Markovian dynamics of the spin states at low temperatures is induced by the memory effects in the decay rates. The non-Markovian oscillation of the Bloch vector is presented. The quantum decoherence can be effectively restrained with the help of the reasonable manipulation of the environment spectral density function and local electric field. The influence of the dissipation on the pointer states are investigated by the von Neumann entropy. The pointer states can be selected by the environment.

quant-ph↗

arXiv2010

Symmetry breaking and criticality in tensor-product states

We discuss variationally optimized matrix-product states for the transverse-field Ising chain, using D*D matrices with small D=2-10. For finite system size N there are energy minimums for symmetric as well as symmetry-broken states, which cross each other at a field value hc(N,D); thus the transition is first-order. A continuous transition develops as N->infinity. The asymptotic critical behavior is then always of mean-field type (the magnetization exponent beta=1/2), but a window of field strengths where true Ising scaling holds (beta=1/8) emerges with increasing D. We also demonstrate asymptotic mean-field behavior for infinite-size two-dimensional tensor-product (iPEPS) states with small tensors.

cond-mat.str-el↗