arXiv subjects

An-Min Wang

Publications and source records attributed to An-Min Wang.

12 recordsLinked to original sources

arXiv2019

Interplay between tilt, disorder, and Coulomb interaction in type-I Dirac fermions

We investigate the mutual influence of tilt, disorder, and Coulomb interaction in a type-I Dirac semimetal (DSM) with $x$-direction tilt by performing a renormalization group analysis. The interplay between disorder and ordinary tilt generates an effective tilt along the $x$-direction, which is the physically observable one. There exist two types of disorder which increase the effective tilt and drive a phase transition from the DSM phase to the diffusive metal phase. The diffusive phase transition stops the increase of the effective tilt and the surface of the original Dirac cone in the diffusive metal phase is just slightly tilted. Surprisingly, the Dirac point is replaced by a bulk nodal arc in the diffusive metal phase. The Coulomb interaction suppresses the diffusive phase transition and therefore is harmful to the formation of bulk nodal arc. In contrast, there also exists other two types of disorder which reduce the effective tilt and induce no phase transition. For these two types of disorder, the Coulomb interaction enhances their low-energy relevances. Coexistence of Coulomb interaction with any of them leads to a stable infrared fixed point where the coupling strengths for two kinds of interaction are identical and the effective tilt vanishes. The original tilted Dirac semimetal now reacts like an untilted and interaction-free Dirac semimetal. Our results show that interplay between tilt, disorder, and Coulomb interaction results in rich low-energy properties for the tilted Dirac fermions.

cond-mat.str-el↗

arXiv2019

Study on Estimating Quantum Discord by Neural Network with Prior Knowledge

Machine learning has achieved success in many areas because of its powerful fitting ability, so we hope it can help us to solve some significant physical quantitative problems, such as quantum correlation. In this research we will use neural networks to predict the value of quantum discord. Quantum discord is a measure of quantum correlation which is defined as the difference between quantum mutual information and classical correlation for a bipartite system. Since the definition contains an optimization term, it makes analytically solving hard. For some special cases and small systems, such as two-qubit systems and some X-states, the explicit solutions have been calculated. However, for general cases, we still know very little. Therefore, we study the feasibility of estimating quantum discord by machine learning method on two-qubit systems. In order to get an interpretable and high performance model, we modify the ordinary neural network by introducing some prior knowledge which come from the analysis about quantum discord. Our results show that prior knowledge actually improve the performance of neural network.

quant-ph↗

arXiv2018

Condition for the emergence of a bulk Fermi arc in disordered Dirac-fermion systems

We present a renormalization group analysis of the disorder effects on the low-energy behaviors of twodimensional tilted Dirac-fermion systems, in which the fermions have two distinct orbitals unrelated by any symmetry. Four types of disordered potential, two interorbital and two intraorbital, are considered. If there is only one type of interorbital disorder, the fermion-disorder scattering induces logarithmic or power-law corrections to the fermion density of states and specific heat. In contrast, the intraorbital disorder can turn the system into a strongly disordered phase. In this disordered phase, calculations based on self-consistent Born approximation reveal that the Dirac point is destroyed and replaced by a bulk Fermi arc. We also study the interplay of four types of disorder, and find that the Dirac point can either remain intact or give place to a Fermi arc. We obtain the condition for the emergence of a Fermi arc in this case. Our results indicate that disorders can result in rich low-energy properties of tilted Dirac fermions.

cond-mat.dis-nn↗

arXiv2018

Next-to-leading order QCD corrections to the decay of Higgs to vector meson and Z boson

The exclusive decay of the Higgs boson to a vector meson ($ J/ψ$ or $ Υ(1S) $) and $ Z $ boson is studied in this work. The decay amplitudes are separated into two parts in a gauge invariant manner. The first part comes from the direct coupling of the Higgs boson to the charm (bottom) quark and the other from the $ HZZ^{*} $ or the loop-induced $ HZγ^{*} $ vertexes in the standard model. While the branching ratios from the direct channel are much smaller than those of the indirect channel, their interference terms give nontrivial contributions. We further calculate the QCD radiative corrections to both channels, which reduce the total branching ratios by around 20% for both $ J/ψ$ and $ Υ(1S) $ production. These results may help to check the SM predictions of the $ H c\bar{c}(H b\bar{b}) $ coupling and to seek for hints of new physics at the High Luminosity LHC or future hadron colliders.

hep-ph↗

arXiv2017

Magneto-optical conductivity of double Weyl semimetals

We investigate the magneto-optical response of double Weyl semimetals whose energy dispersion is intrinsically anisotropic. We find that in the presence of a magnetic field, the most salient feature of the optical conductivity is a series of resonant peaks with the corresponding frequencies scaling linearly with the strength of the magnetic field. In addition, the optical conductivity is found to be anisotropic, with two of the three longitudinal components residing at a linear background and the remaining one at a constant background. The effects of chemical potential, temperature, impurity scattering, and particle-hole symmetry breaking on the optical conductivity are also studied.

cond-mat.mes-hall↗

arXiv2017

Effects of random potentials in three-dimensional quantum electrodynamics

Three-dimensional quantum electrodynamics exhibits a number of interesting properties, such as dynamical chiral symmetry breaking, weak confinement, and non-Fermi liquid behavior, and also has wide applications in condensed matter physics. We study the effects of random potentials, which exist in almost all realistic condensed-matter systems, on the low-energy behaviors of massless Dirac fermions by means of renormalization group method, and show that the role of random mass is significantly enhanced by the gauge interaction, whereas random scalar and vector potentials are insusceptible to the gauge interaction at the one-loop order. The static random potential breaks the Lorentz invariance, and as such induces unusual renormalization of fermion velocity. We then consider the case in which three types of random potentials coexist in the system. The random scalar potential is found to play a dominant role in the low-energy region, and drives the system to undergo a quantum phase transition.

cond-mat.str-el↗

arXiv2016

Interplay of Coulomb interaction and disorder in a two-dimensional semi-Dirac fermion system

It was recently found that Coulomb interaction can induce a series of nontrivial spectral and transport properties in a two-dimensional anisotropic Weyl semimetal. Different from graphehe that is basically an ordinary Fermi liquid, the Coulomb interaction in this system makes the Fermi liquid description invalid over a wide range of energy scales. We present a systematic renormalization group analysis of the interplay of Coulomb interaction and quenched disorder, and show that they have substantial mutual effects on each other, which then leads to a variety of quantum phase transitions and non-Fermi liquid behaviors. The low-energy physics of the system depends sensitively on the effective strength of Coulomb interaction and disorder.

cond-mat.str-el↗

arXiv2015

Matrix product state approach to a frustrated spin chain with long-range interactions

We make extensive simulations over a spin chain model that combines the frustrated $J_1\textrm{-}J_2$ spin chain and the long-range nonfrustrated $(-1)^{(r-1)}r^{-α}$ decay interactions through the variational matrix product state method for both finite and infinite lengths. We study both the ground state entanglement and phase diagram. We find that it is most entangled in the rotation invariant long-range ordered antiferromagnetic phase, where the entanglement scales approximately logarithmically. We determine the development of the Majudar-Ghosh point to a disorder line from entanglement. And we determine approximately the transition from the dimerized and incommensurate phase of the $J_1\textrm{-}J_2$ model to a decoupled phase by studying spin correlation and the dimerization order parameter. Some implications for entanglement in systems with long-range interactions are stated.

cond-mat.str-el↗

arXiv2013

Entanglement entropy in quasi-symmetric multi-qubit states

We generalize the symmetric multi-qubit states to their q-analogs, whose basis vectors are identified with the q-Dicke states. We study the entanglement entropy in these states and find that entanglement is extruded towards certain regions of the system due to the inhomogeneity aroused by q-deformation. We also calculate entanglement entropy in ground states of a related q-deformed Lipkin-Meshkov-Glick model and show that the singularities of entanglement can correctly signify the quantum phase transition points for different strengths of q-deformation.

quant-ph↗

arXiv2013

Remote implementation of partially unknown operations and its entanglement costs

We present the generalized version of Wang's protocol[A.M.Wang, Phys.Rev.A 74,032317 (2006)] for the remote implementation(sometimes referred to as quantum remote control) of partially unknown quantum operations. The protocol only requires no more than half of the entanglements used in Bidirectional Quantum State Teleportation. We also propose a protocol for another form of quantum remote control. It can remotely implement a unitary operation which is a combination of the projective representations of a group. Moreover, we prove that the Schmidt rank of the entanglements cannot not be less than the number of controlled parameters of the operations, which for the first time gives a lower bound on entanglement costs in remote implementation of quantum operations.

quant-ph↗

arXiv2007

Theoretical construction of 1D anyon models

One-dimensional anyon models are renewedly constructed by using path integral formalism. A statistical interaction term is introduced to realize the anyonic exchange statistics. The quantum mechanics formulation of statistical transmutation is presented.

cond-mat.stat-mech↗

arXiv2007

Multi-particle and High-dimension Controlled Order Rearrangement Encryption Protocols

Based on the controlled order rearrange encryption (CORE) for quantum key distribution using EPR pairs[Fu.G.Deng and G.L.Long Phys.Rev.A68 (2003) 042315], we propose the generalized controlled order rearrangement encryption (GCORE) protocols of $N$ qubits and $N$ qutrits, concretely display them in the cases using 3-qubit, 2-qutrit maximally entangled basis states. We further indicate that our protocols will become safer with the increase of number of particles and dimensions. Moreover, we carry out the security analysis using quantum covariant cloning machine for the protocol using qutrits. Although the applications of the generalized scheme need to be further studied, the GCORE has many distinct features such as great capacity and high efficiency.

quant-ph↗