arXiv subjects

Pei Wang

Publications and source records attributed to Pei Wang.

At least 271 records · Page 15Linked to original sources

arXiv2016

One-way quantum computing with arbitrarily large time-frequency continuous-variable cluster states from a single optical parametric oscillator

One-way quantum computing is experimentally appealing because it requires only local measurements on an entangled resource called a cluster state. Record-size, but non-universal, continuous-variable cluster states were recently demonstrated separately in the time and frequency domains. We propose to combine these approaches into a scalable architecture in which a single optical parametric oscillator and simple interferometer entangle up to ($3\times 10^3$ frequencies) $\times$ (unlimited number of temporal modes) into a new and computationally universal continuous-variable cluster state. We introduce a generalized measurement protocol to enable improved computational performance on this new entanglement resource.

quant-ph↗

arXiv2016

Phase diagram of the off-diagonal Aubry-André model

We study a one-dimensional quasiperiodic system described by the off-diagonal Aubry-André model and investigate its phase diagram by using the symmetry and the multifractal analysis. It was shown in a recent work ({\it Phys. Rev. B} {\bf 93}, 205441 (2016)) that its phase diagram was divided into three regions, dubbed the extended, the topologically-nontrivial localized and the topologically-trivial localized phases, respectively. Out of our expectation, we find an additional region of the extended phase which can be mapped into the original one by a symmetry transformation. More unexpectedly, in both "localized" phases, most of the eigenfunctions are neither localized nor extended. Instead, they display critical features, that is, the minimum of the singularity spectrum is in a range $0<γ_{min}<1$ instead of $0$ for the localized state or $1$ for the extended state. Thus, a mixed phase is found with a mixture of localized and critical eigenfunctions.

cond-mat.dis-nn↗

arXiv2016

Discovery of Two New Pulsars in 47 Tucanae (NGC 104)

We report the discovery of two new millisecond pulsars (PSRs J0024$-$7204aa and J0024$-$7204ab) in the globular cluster 47\,Tucanae (NGC 104). Our results bring the total number of pulsars in 47\,Tucanae to 25. These pulsars were discovered by reprocessing archival observations from the Parkes radio telescope. We reprocessed the data using a standard search procedure based on the PRESTO software package as well as using a new method in which we incoherently added the power spectra corresponding to $\sim$1100\,hr of observations. The newly discovered PSR~J0024$-$7204aa, has a pulse frequency of $\rm \sim$541\,Hz (corresponding to a $\rm \sim$1.84 ms period), which is higher than any other pulsars currently known in the cluster and ranks 12$^{\rm{th}}$ amongst all the currently known pulsars. The dispersion measure of this pulsar, 24.941(7)\,cm$^{-3}$ pc, is the highest in the cluster. The second discovered pulsar, PSR~J0024$-$7204ab, is an isolated pulsar with a pulse frequency of $\rm \sim$270\,Hz (corresponding to a period of $\rm \sim$3.70 ms).

astro-ph.HE↗

arXiv2016

Numerically Fitting The Electron Fermi Energy and The Electron Fraction in A Neutron Star

Based on the basic definition of Fermi energy of degenerate and relativistic electrons, we obtain a special solution to electron Fermi energy, $E_{\rm F}(e)$, and express $E_{\rm F}(e)$ as a function of electron fraction, $Y_{e}$, and matter density, $ρ$. Several useful analytical formulae for $Y_{e}$ and $ρ$ within classical models and the work of Dutra et al. 2014 (Type-2) in relativistic mean field theory are obtained using numerically fitting. When describing the mean-field Lagrangian, density, we adopt the TMA parameter set, which is remarkably consistent with with the updated astrophysical observations of neutron stars. Due to the importance of the density dependence of the symmetry energy, $S$, in nuclear astrophysics, a brief discussion on the symmetry parameters $S_v$ and $L$ (the slope of $S$) is presented. Combining these fit formulae with boundary conditions for different density regions, we can evaluate the value of $E_{\rm F}(e)$ in any given matter density, and obtain a schematic diagram of $E_{\rm F}(e)$ as a continuous function of $ρ$. Compared with previous study on the electron Fermi energy in other models, our methods of calculating $E_{\rm F}(e)$ are more simple and convenient, and can be universally suitable for the relativistic electron regions in the circumstances of common neutron stars. We have deduced a general expression of $E_{\rm F}(e)$ and $n_{e}$, which could be used to indirectly test whether one EoS of a NS is correct in our future studies on neutron star matter properties. Since URCA reactions are expected in the center of a massive star due to high-value electron Fermi energy and electron fraction, this study could be useful in the future studies on the NS thermal evolution.

astro-ph.HE↗

arXiv2016

Higgs amplitude mode in massless Dirac fermion systems

The Higgs amplitude mode in superconductors is the condensed matter analogy of Higgs bosons in particle physics. We investigate the time evolution of Higgs amplitude mode in massless Dirac systems, induced by a weak quench of an attractive interaction. We find that the Higgs amplitude mode in the half-filling honeycomb lattice has a logarithmic decaying behaviour, qualitatively different from the $1/\sqrt{t}$ decay in the normal superconductors. Our study is also extended to the doped cases in honeycomb lattice. As for the 3D Dirac semimetal at half filling, we obtain an undamped oscillation of the amplitude mode. Our finding is not only an important supplement to the previous theoretical studies on normal fermion systems, but also provide an experimental signature to characterize the superconductivity in 2D or 3D Dirac systems.

cond-mat.supr-con↗

arXiv2016

A Mixed-effects Model for Incomplete Data With Batch-Level Abundance-Dependent Missing-Data Mechanism

In mass spectrometry based quantitative proteomics research, the emerging iTRAQ technique has been widely adopted for high throughput protein profiling, as it enables one to measure multiple samples simultaneously in one multiplex experiment and thus greatly enhances the throughput of protein quantification. However, the technical variation across different iTRAQ multiplex experiments is often large due to the dynamic nature of MS instruments. This leads to strong batch effects in the iTRAQ data. Moreover, the iTRAQ data often contain substantial batch-level non-ignorable missingness. Specifically, the abundance measures of a given protein/peptide are often missing altogether in all the samples from the same batch, with the missing probability depending on the combined batch-level abundances. We term this unique missing-data mechanism as the Batch-level Abundance-Dependent Missing-data mechanism (BADMM). We introduce a new method, mixEMM, for analyzing iTRAQ data with batch effects and batch-level non-ignorable missingness. The mixEMM method employs a linear mixed-effects model and explicitly models the batch effects and the BADMM in the likelihood function. With simulation studies, we showed that compared with existing approaches that utilize relative abundances and ignore the missing batches under the missing completely at random assumption, the mixEMM method achieves more accurate parameter estimation and inference.We applied the method to an iTRAQ proteomics data from a breast cancer study and identified phosphopeptides differentially expressed between different breast cancer subtypes. The method can be applied to general clustered data with cluster level non ignorable missing-data mechanisms.

stat.AP↗

arXiv2016

Translingual Obfuscation

Program obfuscation is an important software protection technique that prevents attackers from revealing the programming logic and design of the software. We introduce translingual obfuscation, a new software obfuscation scheme which makes programs obscure by "misusing" the unique features of certain programming languages. Translingual obfuscation translates part of a program from its original language to another language which has a different programming paradigm and execution model, thus increasing program complexity and impeding reverse engineering. In this paper, we investigate the feasibility and effectiveness of translingual obfuscation with Prolog, a logic programming language. We implement translingual obfuscation in a tool called BABEL, which can selectively translate C functions into Prolog predicates. By leveraging two important features of the Prolog language, i.e., unification and backtracking, BABEL obfuscates both the data layout and control flow of C programs, making them much more difficult to reverse engineer. Our experiments show that BABEL provides effective and stealthy software obfuscation, while the cost is only modest compared to one of the most popular commercial obfuscators on the market. With BABEL, we verified the feasibility of translingual obfuscation, which we consider to be a promising new direction for software obfuscation.

cs.CR↗

arXiv2015

Identifying the closeness of eigenstates in quantum many-body systems

We propose a new quantity called modulus fidelity to measure the closeness of two quantum pure states. Especially, we use it to investigate the closeness of eigenstates of quantum many-body systems. When the system is integrable, the modulus fidelity of neighbor eigenstates displays a large fluctuation. But the modulus fidelity is close to a constant when system becomes non-integrable with fluctuation reduced drastically. Average modulus fidelity of neighbor eigenstates increases with the increase of parameters that destroy the integrability, which also indicates the integrable-chaos transition. In non-integrable case, it is found two eigenstates are closer to each other if their level spacing is small. We also show that the closeness of eigenstates in non-integrable domain is the underlying mechanism of \emph{eigenstate thermalization hypothesis} (ETH) which explains the thermalization in nonintegrable system we studied.

cond-mat.stat-mech↗

arXiv2015

Universal nonanalytic behavior of the Hall conductance in a Chern insulator at the topologically driven nonequilibrium phase transition

We study the Hall conductance of a Chern insulator after a global quench of the Hamiltonian. The Hall conductance in the long time limit is obtained by applying the linear response theory to the diagonal ensemble. It is expressed as the integral of the Berry curvature weighted by the occupation number over the Brillouin zone. We identify a topologically driven nonequilibrium phase transition, which is indicated by the nonanalyticity of the Hall conductance as a function of the energy gap m_f in the post-quench Hamiltonian H_f. The topological invariant for the quenched state is the winding number of the Green's function W, which equals the Chern number for the ground state of H_f. In the limit that m_f goes to zero, the derivative of the Hall conductance with respect to m_f is proportional to ln(|m_f|), with the constant of proportionality being the ratio of the change of W at m_f = 0 to the energy gap in the initial state. This nonanalytic behavior is universal in two-band Chern insulators such as the Dirac model, the Haldane model, or the Kitaev honeycomb model in the fermionic basis.

cond-mat.quant-gas↗

arXiv2015

Topologically driven nonequilibrium phase transitions in diagonal ensembles

We identify a new class of topologically driven phase transitions when calculating the Hall conductance of two-band Chern insulators in the long-time limit after a global quench of the Hamiltonian. The Hall conductance is expressed as the integral of the Berry curvature in the diagonal ensemble. Even if the topological invariant of the wave function is conserved under unitary evolution, the Hall conductance as a function of the energy gap in the post-quench Hamiltonian displays a continuous but nonanalytic behavior, that is it has a logarithmically divergent derivative as the gap closes. The coefficient of this logarithmic function is the ratio of the change of Chern number in the ground state of the post-quench Hamiltonian to the energy gap in the initial state. This nonanalytic behavior is universal in two-band Chern insulators.

cond-mat.quant-gas↗

arXiv2015

FFLO state with angle dependent Gap in Asymmetric Nuclear Matter

We consider the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state with an angle dependent-gap (ADG) for the arbitrary angle θ_0 between the direction of the Cooper pair momentum and the symmetry axis of the ADG in asymmetric nuclear matter. We find two kinds of locally stable states, i.e., the FFLO-ADG-orthogonal and FFLO-ADG-parallel states, which correspond to θ_0=π/2 and θ_0=0, respectively. Furthermore, the-FFLO-ADG-orthogonal state is located at small asymmetry, whereas the FFLO-ADG-parallel state is favored for large asymmetry. The critical isospin asymmetry α_c, where the superfluid vanishes, is enhanced largely by considering the Cooper pair momentum with an ADG.

nucl-th↗

arXiv2015

Engineering large-scale entanglement in the quantum optical frequency comb: influence of the quasiphasematching bandwidth and of dispersion

One of the most scalable methods for continuous-variable quantum computing is to encode quantum information in the quantum optical frequency comb generated by an optical parametric oscillator (OPO). The scalability is limited by the quasiphasematching bandwidth and dispersion of the OPO. We study both factors in this article. The results show that 3200 qumodes are probably entangled in our recent demonstration of a record 60-qumode entanglement.

physics.optics↗

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

Identify the topological superconducting order in a multi-band quantum wire

How to distinguish the zero-bias peak (ZBP) caused by the Majorana fermions from that by the other effects remains a challenge in detecting the topological order of a quantum wire. In this paper we propose to distinguish the topological superconducting phase from the topologically trivial phase by making a Josephson junction of the quantum wire attached to a side lead and then measuring the tunneling conductance through it as the phase difference across the junction $ϕ$ varies. Even if the ZBPs exist in both phases, we can identify the topological superconducting phase by a conductance peak at $ϕ=π$ and a nearby butterfly pattern.

cond-mat.mes-hall↗

arXiv2014

Numerical operator method for the real time dynamics of strongly-correlated quantum impurity systems far from equilibrium

We develop a method for studying the real time dynamics of Heisenberg operators in strongly-interacting nonequilibrium quantum impurity models. Our method is applicable to a wide range of interaction strengths and to bias voltages beyond the linear response regime, works at zero temperature, and overcomes the finite-size limitations faced by other numerical methods. We compare our method with quantum Monte Carlo simulations at a strong interaction strength, at which no analytical method is applicable up to now. We find a very good coincidence of the results at high bias voltage, and in the short time period at low bias voltage. We discuss the possible reason of the deviation in the long time period at low bias voltage. We also find a good coincidence of our results with the perturbation results at weak interactions.

cond-mat.str-el↗

arXiv2014

Weaving quantum optical frequency combs into continuous-variable hypercubic cluster states

Cluster states with higher-dimensional lattices that cannot be physically embedded in three-dimensional space have important theoretical interest in quantum computation and quantum simulation of topologically ordered condensed-matter systems. We present a simple, scalable, top-down method of entangling the quantum optical frequency comb into hypercubic-lattice continuous-variable cluster states of a size of about 10^4 quantum field modes, using existing technology. A hypercubic lattice of dimension D (linear, square, cubic, hypercubic, etc.) requires but D optical parametric oscillators with bichromatic pumps whose frequency splittings alone determine the lattice dimensionality and the number of copies of the state.

quant-ph↗

arXiv2014

Topological phase transition in the quench dynamics of a one-dimensional Fermi gas

We study the quench dynamics of a one-dimensional ultracold Fermi gas in an optical lattice potential with synthetic spin-orbit coupling. At equilibrium, the ground state of the system can undergo a topological phase transition and become a topological superfluid with Majorana edge states. As the interaction is quenched near the topological phase boundary, we identify an interesting dynamical phase transition of the quenched state in the long-time limit, characterized by an abrupt change of the pairing gap at a critical quenched interaction strength. We further demonstrate the topological nature of this dynamical phase transition from edge-state analysis of the quenched states. Our findings provide interesting clues for the understanding of topological phase transitions in dynamical processes, and can be useful for the dynamical detection of Majorana edge states in corresponding systems.

cond-mat.quant-gas↗

arXiv2014

The transport properties of Floquet topological superconductors at the transition from the topological phase to the Anderson localized phase

The Floquet topological superconducting state is a nonequilibrium time-periodic state hosting Majorana fermions. We study its transport properties by using the Kitaev model with time-periodic incommensurate potentials, which experiences phase transition from the Floquet topological superconducting phase to the Anderson localized phase with increasing driving strength. We study both the real time dynamics of the current and the non-analytic behavior of the tunneling conductance at the transition. Especially, we find that the tunneling conductance changes continuously at the transition, being a finite value in the presence of Floquet Majorana fermions, but dropping to zero as the Majorana fermions vanish. For a special choice of parameters, the Majorana fermions revive at larger driving strength, accompanied by the revival of conductances.

cond-mat.mes-hall↗