arXiv subjects

Bin Chen

Publications and source records attributed to Bin Chen.

At least 667 records · Page 37Linked to original sources

arXiv2015

Large Interval Limit of Rényi Entropy At High Temperature

In this paper, we propose a novel expansion to compute the large interval limit of the Rényi entropy of 2D CFT at high temperature. Via the replica trick, the single interval Rényi entropy of 2D CFT at finite temperature could be read from the partition function on $n$-sheeted torus connected with each other along a branch cut. We calculate the partition function by inserting a complete basis across the branch cut. Because of the monodromy condition across the branch cut in the large interval limit, the basis of the states should be the ones in the twist sector. We study the twist sector of a general module of CFT and find that there is an one-to-one correspondence between the twist sector states and the normal sector states. As an application, we revisit the non-compact free scalar theory and discuss the large interval limit of the Rényi entropy of this theory by using our proposal. We find complete agreement in the leading and next-leading orders with direct expansion of the exact partition function. Moreover, we prove the relation (\ref{th}) between thermal entropy and the entanglement entropy for a generic CFT with discrete spectrum.

hep-th↗

arXiv2015

Holographic Calculation for Large Interval Rényi Entropy at High Temperature

In this paper, we study the holographic Rényi entropy of a large interval on a circle at high temperature for the two-dimensional conformal field theory (CFT) dual to pure AdS$_3$ gravity. In the field theory, the Rényi entropy is encoded in the CFT partition function on $n$-sheeted torus connected with each other by a large branch cut. As proposed by Chen and Wu [Large interval limit of Rényi entropy at high temperature, arXiv:1412.0763], the effective way to read the entropy in the large interval limit is to insert a complete set of state bases of the twist sector at the branch cut. Then the calculation transforms into an expansion of four-point functions in the twist sector with respect to $e^{-\frac{2πTR}{n}}$. By using the operator product expansion of the twist operators at the branch points, we read the first few terms of the Rényi entropy, including the leading and next-to-leading contributions in the large central charge limit. Moreover, we show that the leading contribution is actually captured by the twist vacuum module. In this case by the Ward identity the four-point functions can be derived from the correlation function of four twist operators, which is related to double interval entanglement entropy. Holographically, we apply the recipe in [T. Faulkner, The entanglement Rényi entropies of disjoint intervals in AdS/CFT, arXiv:1303.7221] and [T. Barrella et al., Holographic entanglement beyond classical gravity, J. High Energy Phys. 09 (2013) 109] to compute the classical Rényi entropy and its one-loop quantum correction, after imposing a new set of monodromy conditions. The holographic classical result matches exactly with the leading contribution in the field theory up to $e^{-4πTR}$ and $l^6$, while the holographical one-loop contribution is in exact agreement with next-to-leading results in field theory up to $e^{-\frac{6πTR}{n}}$ and $l^4$ as well.

hep-th↗

arXiv2015

Sum uncertainty relations for arbitrary $N$ incompatible observables

We formulate uncertainty relations for arbitrary $N$ observables. Two uncertainty inequalities are presented in terms of the sum of variances and standard deviations, respectively. The lower bounds of the corresponding sum uncertainty relations are explicitly derived. These bounds are shown to be tighter than the ones such as derived from the uncertainty inequality for two observables [Phys. Rev. Lett. 113, 260401 (2014)]. Detailed examples are presented to compare among our results with some existing ones.

quant-ph↗

arXiv2015

One loop partition function in AdS_3/CFT_2

The 1-loop partition function of the handle-body solutions in the AdS$_3$ gravity have been derived some years ago using the heat-kernel and the method of images. In the semiclassical limit, such partition function should correspond to the order $O (c^0)$ part in the partition function of dual conformal field theory on the boundary Riemann surface. The higher genus partition function could be computed by the multi-point functions in the Riemann sphere via sewing prescription. In the large central charge limit, to the leading order of $c$, the multi-point function is further simplified to be a summation over the product of two-point functions, which may form links. Each link is in one-to-one correspondence with the conjugacy class of the Schottky group of the Riemann surface. Moreover, the value of a link is determined by the eigenvalue of the element in the conjugate class. This allows us to reproduce exactly the gravitational 1-loop partition function. The proof can be generalized to the higher spin gravity and its dual CFT.

hep-th↗

arXiv2015

Multi-Fields Modulation of Physical Properties of Oxide Thin Films

Oxide thin films exhibit versatile physical properties such as magnetism, ferroelectricity, piezoelectricity, metal-insulator transition (MIT), multiferroicity, colossal magnetoresistivity, switchable resistivity, etc. More importantly, the exhibited multifunctionality could be tuned by various external fields, which has enabled demonstration of novel electronic devices. In this article, recent studies of the multi-fields modulation of physical properties in oxide thin films have been reviewed. Some of the key issues and prospects about this field are also addressed.

cond-mat.mtrl-sci↗

arXiv2015

Superconductivity in a new layered nickel-selenide CsNi2Se2

The physical properties of CsNi$_{2}$Se$_{2}$ were characterized by electrical resistivity, magnetization and specific heat measurements. We found that the stoichiometric CsNi$_{2}$Se$_{2}$ compound is a superconductor with a transition temperature \textit{T$_{c}$}=2.7K. A large Sommerfeld coefficient $γ$$_{n}$ ($\sim$77.90 mJ/mol$\cdot$K$^{-2}$), was obtained from the normal state electronic specific heat. However, the Kadowaki-Woods ratio of CsNi$_{2}$Se$_{2}$ was estimated to be about 0.041$\times$10$^{-5}$ $μΩ$$\cdot$cm(mol$\cdot$K/mJ)$^{2}$, indicating the absence of strong electron-electron correlations in this compound. In the superconducting state, we found that the zero-field electronic specific heat data, $C_{es}(T)$ (0.5K $\leq$ T $<$ 2.6K), can be well fitted with a two-gap BCS model. The comparison with the results of the density functional theory (DFT) calculations suggested that the large $γ$$_{n}$ in the nickel-selenide superconductors may be related to the large Density of States (DOS) at the fermi surface.

cond-mat.supr-con↗

arXiv2015

Entanglement Entropy for Descendent Local Operators in 2D CFTs

We mainly study the Rényi entropy and entanglement entropy of the states locally excited by the descendent operators in two dimensional conformal field theories (CFTs). In rational CFTs, we prove that the increase of entanglement entropy and Rényi entropy for a class of descendent operators, which are generated by $\cal{L}^{(-)}\bar{\cal{L}}^{(-)}$ onto the primary operator, always coincide with the logarithmic of quantum dimension of the corresponding primary operator. That means the Rényi entropy and entanglement entropy for these descendent operators are the same as the ones of their corresponding primary operator. For 2D rational CFTs with a boundary, we confirm that the Rényi entropy always coincides with the logarithmic of quantum dimension of the primary operator during some periods of the evolution. Furthermore, we consider more general descendent operators generated by $\sum_{} d_{\{n_i\}\{n_j\}}(\prod_{i} L_{-n_i}\prod_{j}{\bar L}_{-n_j})$ on the primary operator. For these operators, the entanglement entropy and Rényi entropy get additional corrections, as the mixing of holomorphic and anti-holomorphic Virasoro generators enhance the entanglement. Finally, we employ perturbative CFT techniques to evaluate the Rényi entropy of the excited operators in deformed CFT. The Rényi and entanglement entropies are increased, and get contributions not only from local excited operators but also from global deformation of the theory.

hep-th↗

arXiv2015

Temporal evolution of chromospheric evaporation: case studies of the M1.1 flare on 2014 September 6 and X1.6 flare on 2014 September 10

With observations from the Interface Region Imaging Spectrograph (IRIS), we track the complete evolution of $\sim$11 MK evaporation flows in an M1.1 flare on 2014 September 6 and an X1.6 flare on 2014 September 10. These hot flows, as indicated by the blueshifted Fe~{\sc{xxi}}~1354.08Å~line, evolve smoothly with a velocity decreasing exponentially from $\sim$200~km~s$^{-1}$ to almost stationary within a few minutes. We find a good correlation between the flow velocity and energy deposition rate as represented by the hard X-Ray flux observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), or time derivative of the soft X-Ray flux observed with the Geostationary Operational Environmental Satellites (GOES) and the HINODE X-ray Telescope (XRT), which is in general agreement with models of nonthermal electron heating. The maximum blue shift of Fe~{\sc{xxi}}~appears approximately at the same time as or slightly after the impulsive enhancement of the ultraviolet continuum and the Mg~{\sc{ii}}~2798.8Å~line emission, demonstrating that the evaporation flow is closely related to heating of the lower chromosphere. Finally, while the hot Fe~{\sc{xxi}}~1354.08Å line is entirely blueshifted with no obvious rest component, cool chromospheric and transition region lines like Si~{\sc{iv}}~1402.77Å are often not entirely redshifted but just reveal an obvious red wing enhancement at the ribbons, suggesting that the speed of chromospheric condensation might be larger than previously thought.

astro-ph.SR↗

arXiv2015

Unsaturated both large positive and negative magnetoresistance in Weyl Semimetal TaP

After growing successfully TaP single crystal, we measured its longitudinal resistivity (rhoxx) and Hall resistivity (rhoyx) at magnetic fields up to 9T in the temperature range of 2-300K. It was found that at 2K its magnetoresistivity (MR) reaches to 328000 percent, at 300K to 176 percent at 8T, and both do not appear saturation. We confirmed that TaP is indeed a low carrier concentration, hole-electron compensated semimetal, with a high mobility of hole muh=371000 cm2V-1s-1, and found that a magnetic-field-induced metal-insulator transition occurs at room temperature. Remarkably, as a magnetic field (H) is applied in parallel to the electric field (E), the negative MR due to chiral anomaly is observed, and reaches to -3000 percent at 9T without any signature of saturation, too, which distinguishes with other Weyl semimetals (WSMs). The analysis on the Shubnikov-de Haas (SdH) oscillations superimposing on the MR reveals that a nontrivial Berry phase with strong offset of 0.3958 realizes in TaP, which is the characteristic feature of the charge carriers enclosing a Weyl nodes. These results indicate that TaP is a promising candidate not only for revealing fundamental physics of the WSM state but also for some novel applications.

cond-mat.str-el↗

arXiv2015

Holographic Rényi Entropy of Single Interval on Torus: with W symmetry

In this paper, we extend our study of the holographic Rényi entropy of single interval on a torus to the CFT with W symmetry. To read the possible corrections from W fields clearly, we compute the thermal correction to the Rényi entropy up to the order $e^{-8π/TL}$. In the field theory, this requires us to compute the contribution from all the level 4 states, from both the vacuum module and W primaries. On the gravity side, after computing the eigenvalue of single Schottky generators to the order $e^{-4 π/TL}$, we obtain the 1-loop quantum correction to the holographic Rényi entropy. We find complete agreement between the bulk and boundary theories.

hep-th↗

arXiv2015

Spin-orbit engineering in transition metal dichalcogenide alloy monolayers

Transition metal dichalcogenide (TMDC) monolayers are newly discovered semiconductors for a wide range of applications in electronics and optoelectronics. Most studies have focused on binary monolayers that share common properties: direct optical bandgap, spin-orbit (SO) splittings of hundreds of meV, light-matter interaction dominated by robust excitons and coupled spin-valley states of electrons. Studies on alloy-based monolayers are more recent, yet they may not only extend the possibilities for TMDC applications through specific engineering but also help understanding the differences between each binary material. Here, we synthesized highly crystalline Mo$_{(1-x)}$W$_{x}$Se$_2$ to show engineering of the direct optical bandgap and the SO coupling in ternary alloy monolayers. We investigate the impact of the tuning of the SO spin splitting on the optical and polarization properties. We show a non-linear increase of the optically generated valley polarization as a function of tungsten concentration, where 40% tungsten incorporation is sufficient to achieve valley polarization as high as in binary WSe2. We also probe the impact of the tuning of the conduction band SO spin splitting on the bright versus dark state population i.e. PL emission intensity. We show that the MoSe2 PL intensity decreases as a function of temperature by an order of magnitude, whereas for WSe2 we measure surprisingly an order of magnitude increase over the same temperature range (T=4-300K). The ternary material shows a trend between these two extreme behaviors. These results show the strong potential of SO engineering in ternary TMDC alloys for optoelectronics and applications based on electron spin- and valley-control.

cond-mat.mtrl-sci↗

arXiv2015

Detection of Ideal Resource for Multiqubit Teleportation

We give a sufficient condition in detecting entanglement resource for perfect multiqubit teleportation. The criterion involves only local measurements on some complementary observables and can be experimentally implemented. It is also a necessary condition for fully separability of multiqubit states. Moreover, by proving the optimality of teleportation witnesses, we solve the open problem in [Phys. Rev. A {\bf 86}, 032315 (2012)].

quant-ph↗

arXiv2015

Holographical Description of BPS Wilson Loops in Flavored ABJM Theory

As holographic description of BPS Wilson loops in ${\cal N}=3$ flavored ABJM theory with $N_f=k=1$, BPS M2-branes in $AdS_4\times N(1, 1)$ are studied in details. Two $1/3$-BPS membrane configurations are found. One of them is dual to the $1/3$-BPS Wilson loop of Gaiotto-Yin type. The regulated membrane action captures precisely the leading exponential behavior of the vacuum expectation values of $1/3$-BPS Wilson loops in the strong coupling limit, which was computed before using supersymmetric localization technique. Moreover, there is no BPS membrane with more supersymmetries in the background, under quite natural assumption on the membrane worldvolume. This suggests that there is no Wilson loop preserving more than 1/3 supersymmetries in such flavored ABJM theory.

hep-th↗

arXiv2015

Superconductivity and Disorder Effect in TlNi$_2$Se$_{2-x}$S$_x$ crystals

After our first discovery of superconductivity (SC) with $T_C$=3.7 K in TlNi$_2$Se$_2$, we grew successfully a series of TlNi$_2$Se$_{2-x}$S$_x$ (0.0 $\leq$ x $\leq$2.0) single crystals. The measurements of resistivity, susceptibility and specific heat were carried out. We found that SC with $T_C$=2.3 K also emerges in TlNi$_2$S$_2$ crystal, which appears to involve heavy electrons with an effective mass $m^*$=13$\sim$25 $m_b$, as inferred from the normal state electronic specific heat and the upper critical field, $H_{C2}(T)$. It was found that the $T_C$ and superconducting volume fraction in TlNi$_2$Se$_{2-x}$S$_x$ crystals changes with the disorder degree induced by the partial substitution of S for Se, which is characterized by the residual resistivity ratio (\textit{RRR}). The effect of the disorder on SC may provide some information for understanding the mechanism of SC in this new Ni-chalcogenide system.

cond-mat.supr-con↗

arXiv2015

Algorithms And Programs For Strong Gravitational Lensing In Kerr Space-time Including Polarization

Active galactic nuclei (AGNs) and quasars are important astrophysical objects to understand. Recently, microlensing observations have constrained the size of the quasar X-ray emission region to be of the order of 10 gravitational radii of the central supermassive black hole. For distances within a few gravitational radii, light paths are strongly bent by the strong gravity field of the central black hole. If the central black hole has nonzero angular momentum (spin), a photon's polarization plane will be rotated by the gravitational Faraday effect. The observed X-ray flux and polarization will then be influenced significantly by the strong gravity field near the source. Consequently, linear gravitational lensing theory is inadequate for such extreme circumstances. We present simple algorithms computing strong lensing effects of Kerr black holes, including effects on polarization. Our algorithms are realized in a program "KERTAP" in two versions: MATLAB and Python. The key ingredients of KERTAP are: a graphic user interface, a {\it backward} ray-tracing algorithm, a polarization propagator dealing with gravitational Faraday rotation, and algorithms computing observables such as flux magnification and polarization angles. Our algorithms can be easily realized in other programming languages such as FORTRAN, C, and C++. The MATLAB version of KERTAP is parallelized using the MATLAB Parallel Computing Toolbox and the Distributed Computing Server. The Python code was sped up using Cython and supports full implementation of MPI using 'mpi4py' package. As an example, we investigate the inclination angle dependence of the observed polarization and the strong lensing magnification of AGN X-ray emission. We conclude that it is possible to perform complex numerical-relativity-related computations using interpreted languages such as MATLAB and Python.

astro-ph.HE↗

arXiv2015

Universal relation between thermal entropy and entanglement entropy in CFT

Inspired by the holographic computation of large interval entanglement entropy of two dimensional conformal field theory at high temperature, it was proposed that the thermal entropy is related to the entanglement entropy as $S_{th}=\displaystyle{\lim_{l \to 0}(S_{EE}(R-l)-S_{EE}(l))}$. In this letter, we prove this relation for 2D CFT with discrete spectrum in two different ways. Moreover we discuss this relation for a 2D noncompact free scalar, which is a gapless CFT with continuous spectrum. We show that it could be recovered, after appropriately regularizing the theory.

hep-th↗

arXiv2015

Probing the integrated Sachs-Wolfe effect using embedded lens models

The photometry profile of the integrated Sachs-Wolfe (ISW) effect recently obtained by the Planck consortium by stacking patches of Cosmic Microwave Background (CMB) sky maps around a large number of cosmic voids, contains a cold ring at about half the void's effective radius surrounded by a hot ring near the void's boundary. The source of the temperature structure is assumed to be the ISW effect but the exact cause of the ringed structure is not currently well understood, particularly the outer hot ring. Numerical simulations have suggested that hot/cold ring structures can be produced by motions associated with nonlinear growths of cosmic structures whose gravitational potentials produce the ISW effect. We have recently developed the embedded lens theory and the Fermat potential formalism which can be used to model the ISW effect caused by intervening individual lens inhomogeneities evolving arbitrarily. This theory only requires knowledge of the void's projected mass profile as a function of the passing CMB photons' impact radius and the rate of change of that mass distribution at passage. We present two simple embedded void lens models with evolving mass densities and investigate the ISW effect caused by these lenses. Both models posses expanding mass shells which produce hot rings around central cold regions, consistent with the recent observations. By adding a small over-density at the void's center we can produce the slight positive temperature excess hinted at in Planck's photometric results. We conclude that the embedded lens theory and the Fermat potential formalism is well suited for modeling the ISW effect.

astro-ph.CO↗

arXiv2015

An integrated Sachs-Wolfe effect vs redshift test for the cosmological parameters

We describe a method using the integrated Sachs-Wolfe (ISW) effect caused by individual inhomogeneities to determine the cosmological parameters, $H_0$, $Ω_{\rm m}$, and $Ω_Λ$, etc. This ISW-redshift test requires detailed knowledge of the internal kinematics of a set of individual density perturbations, e.g., galaxy clusters and/or cosmic voids, in particular their density and velocity profiles, and their mass accretion rates. It assumes the density perturbations are isolated and imbedded (equivalently compensated) and makes use of the newly found relation between the ISW temperature perturbation of the CMB and the Fermat potential of the lens. Given measurements of the amplitudes of the temperature variations in the CMB caused by such clusters or voids at various redshifts and estimates of their angular sizes or masses, one can constrain the cosmological parameters. More realistically, the converse is more likely, i.e., if the background cosmology is sufficiently constrained, measurement of ISW profiles of clusters and voids (e.g., hot and cold spots and rings) can constrain dynamical properties of the dark matter, including accretion, associated with such lenses and thus constrain the evolution of these objects with redshift.

astro-ph.CO↗