Optimized Decimation of Tensor Networks with Super-orthogonalization for Two-Dimensional Quantum Lattice Models

A novel algorithm based on the optimized decimation of tensor networks with super-orthogonalization (ODTNS) that can be applied to simulate efficiently and accurately not only the thermodynamic but also the ground state properties of two-dimensional (2D) quantum lattice models is proposed. By transforming the 2D quantum model into a three-dimensional (3D) closed tensor network (TN) comprised of the tensor product density operator and a 3D brick-wall TN, the free energy of the system can be calculated with the imaginary time evolution, in which the network Tucker decomposition is suggested for the first time to obtain the optimal lower-dimensional approximation on the bond space by transforming the TN into a super-orthogonal form. The efficiency and accuracy of this algorithm are testified, which are fairly comparable with the quantum Monte Carlo calculations. Besides, the present ODTNS scheme can also be applicable to the 2D frustrated quantum spin models with nice efficiency

Cryptanalysis of a multi-party quantum key agreement protocol with single particles

Recently, Sun et al. [Quant Inf Proc DOI: 10.1007/s11128-013-0569-x] presented an efficient multi-party quantum key agreement (QKA) protocol by employing single particles and unitary operations. The aim of this protocol is to fairly and securely negotiate a secret session key among $N$ parties with a high qubit efficiency. In addition, the authors claimed that no participant can learn anything more than his/her prescribed output in this protocol, i.e., the sub-secret keys of the participants can be kept secret during the protocol. However, here we points out that the sub-secret of a participant in Sun et al.'s protocol can be eavesdropped by the two participants next to him/her. In addition, a certain number of dishonest participants can fully determine the final shared key in this protocol. Finally, we discuss the factors that should be considered when designing a really fair and secure QKA protocol.Comment: 7 page

Linearized Tensor Renormalization Group Algorithm for Thermodynamics of Quantum Lattice Models

A linearized tensor renormalization group (LTRG) algorithm is proposed to calculate the thermodynamic properties of one-dimensional quantum lattice models, that is incorporated with the infinite time-evolving block decimation technique, and allows for treating directly the two-dimensional transfer-matrix tensor network. To illustrate its feasibility, the thermodynamic quantities of the quantum XY spin chain are calculated accurately by the LTRG, and the precision is shown to be comparable with (even better than) the transfer matrix renormalization group (TMRG) method. Unlike the TMRG scheme that can only deal with the infinite chains, the present LTRG algorithm could treat both finite and infinite systems, and may be readily extended to boson and fermion quantum lattice models.Comment: published versio

Kosterlitz-Thouless phase transition and reentrance in an anisotropic 3-state Potts model on the generalized Kagome lattice

The unusual reentrant phenomenon is observed in the anisotropic 3-state Potts model on a gen- eralized Kagome lattice. By employing the linearized tensor renormalization group method, we find that the reentrance can appear in the region not only under a partial ordered phase as commonly known but also a phase without a local order parameter, which is uncovered to fall into the uni- versality of the Kosterlitz-Thouless (KT) type. The region of the reentrance depends strongly on the ratios of the next nearest couplings {\alpha} = J2 /|J1 | and {\beta} = J3 /|J1 |. The phase diagrams in the plane of temperature versus {\beta} for different {\alpha} are obtained. Through massive calculations, it is also revealed that the quasi-entanglement entropy can be used to accurately detect the KT transition temperature

dd-wave Superconductivity, Pseudogap, and the Phase Diagram of tt-t′t'-JJ Model at Finite Temperature

Recently, a robust $d$-wave superconductivity has been unveiled in the ground state of the 2D $t$-$t'$-$J$ model -- with both nearest-neighbor ($t$) and next-nearest-neighbor ($t'$) hoppings -- through the density matrix renormalization group calculations in the ground state. In this study, we exploit the state-of-the-art thermal tensor network approach to accurately simulate the finite-temperature electron states of the $t$-$t'$-$J$ model on cylinders with widths up to $W=6$. Our analysis suggests that in the dome-like superconducting phase, the $d$-wave pairing susceptibility exhibits a divergent behavior with $\chi_\textrm{SC} \propto 1/T^\alpha$ below the onset temperature $T_c^*$. Near the optimal doping, $T_c^*$ reaches its highest value of about $0.05 t$ ($\equiv 0.15 J$). Above $T_c^*$ yet below a higher crossover temperature $T^*$, the magnetic susceptibility is suppressed, and the Fermi surface also exhibits node-antinode structure, resembling the pseudogap behaviors observed in cuprates. Our unbiased and accurate thermal tensor network calculations obtain the phase diagram of the $t$-$t'$-$J$ model with $t'/t>0$, shedding light on the $d$-wave superconducting and pseudogap phases in the enigmatic cuprate phase diagram.Comment: 7+5 pages, 4+8 figure

Responses of microbial abundance and enzyme activity in integrated vertical-flow constructed wetlands for domestic and secondary wastewater

Although micro-organisms play a significant role in pollutant removal in constructed wetlands, little is known on the effect of wastewater-quality properties on microbial characteristics. In this study, two groups of integrated vertical-flow constructed wetland microcosms were applied to treat synthetic domestic wastewater and synthetic secondary effluent. The effects of wastewater-quality properties on microbial features were assessed. Results showed that higher values of microbial indicators were observed in the systems with domestic wastewater and in down-flow cells. Redundancy analysis revealed that organic matter concentration and temperature were two critical determinants influencing the microbial features

Web-based computer adaptive assessment of individual perceptions of job satisfaction for hospital workplace employees

<p>Abstract</p> <p>Background</p> <p>To develop a web-based computer adaptive testing (CAT) application for efficiently collecting data regarding workers' perceptions of job satisfaction, we examined whether a 37-item Job Content Questionnaire (JCQ-37) could evaluate the job satisfaction of individual employees as a single construct.</p> <p>Methods</p> <p>The JCQ-37 makes data collection via CAT on the internet easy, viable and fast. A Rasch rating scale model was applied to analyze data from 300 randomly selected hospital employees who participated in job-satisfaction surveys in 2008 and 2009 via non-adaptive and computer-adaptive testing, respectively.</p> <p>Results</p> <p>Of the 37 items on the questionnaire, 24 items fit the model fairly well. Person-separation reliability for the 2008 surveys was 0.88. Measures from both years and item-8 job satisfaction for groups were successfully evaluated through item-by-item analyses by using <it>t</it>-test. Workers aged 26 - 35 felt that job satisfaction was significantly worse in 2009 than in 2008.</p> <p>Conclusions</p> <p>A Web-CAT developed in the present paper was shown to be more efficient than traditional computer-based or pen-and-paper assessments at collecting data regarding workers' perceptions of job content.</p