Graphical representations and worm algorithms for the O(N) spin model

We present a family of graphical representations for the O(N)spin model,where N≥1 represents the spin dimension,and N=1,2,3 corresponds to the Ising,XY and Heisenberg models,respectively.With an integer parameter 0≤ℓ≤N/2,each configuration is the coupling of ℓ copies of subgraphs consisting of directed flows and N−2ℓ copies of subgraphs constructed by undirected loops,which we call the XY and Ising subgraphs,respectively.On each lattice site,the XY subgraphs satisfy the Kirchhoff flow-conservation law and the Ising subgraphs obey the Eulerian bond condition.Then,we formulate worm-type algorithms and simulate the O(N)model on the simple-cubic lattice for N from 2 to 6 at all possibleℓ.It is observed that the worm algorithm has much higher efficiency than the Metropolis method,and,for a given N,the efficiency is an increasing function ofℓ.Besides Monte Carlo simulations,we expect that these graphical representations would provide a convenient basis for the study of the O(N)spin model by other state-of-the-art methods like the tensor network renormalization.

Precision mapping the topological bands of 2D spin-orbit coupling with microwave spin-injection spectroscopy

To investigate the band structure is one of the key approaches to study the fundamental properties of a novel material.We report here the precision band mapping of a 2-dimensional(2D) spin-orbit(SO) coupling in an optical lattice.By applying the microwave spin-injection spectroscopy, the band structure and spin-polarization distribution are achieved simultaneously.The band topology is also addressed with observing the band gap close and re-open at the Dirac points.Furthermore, the lattice depth and the Raman coupling strength are precisely calibrated with relative errors in the order of 10^(-3).Our approach could also be applied for exploring the exotic topological phases with even higher dimensional system.

Simultaneous analysis of three-dimensional percolation models

We simulate the bond and site percolation models on several three-dimensional lattices, including the diamond, body-centered cubic, and face-centered cubic lattices. As on the simple-cubic lattice [Phys. Rev. E, 2013, 87（5）： 052107], it is observed that in comparison with dimensionless ratios based on cluster-size distribution, certain wrapping probabilities exhibit weaker finite-size corrections and are more sensitive to the deviation from percolation threshold Pc, and thus provide a powerful means for determining Pc. We analyze the numerical data of the wrapping probabilities simultaneously such that universal parameters are shared by the aforementioned models, and thus significantly improved estimates of Pc are obtained.

Irreversible Markov chain Monte Carlo algorithm for self-avoiding walk

We formulate an irreversible Markov chain Monte Carlo algorithm for the self-avoiding walk （SAW）, which violates the detailed balance condition and satisfies tile balance condition. Its performance improves significantly compared to that of the Berretti-Sokal algorithm, which is a variant of the Metropolis Hastings method. The gained efficiency increases with spatial dimension （D）, from approximately 10 times in 2D to approximately 40 times in 5D. We simulate the SAW on a 5D hypercubic lattice with periodic boundary conditions, for a linear system with a size up to L = 128, and confirm that as for the 5D Ising model, the finite-size scaling of the SAW is governed by renormalized exponents, υ^＊ = 2/d and γ/υ^＊ = d/2. The critical point is determined, which is approximately 8 times more precise than the best available estimate.

费米超流体的类振荡膨胀（英文）

在强相互作用的费米气体的研究中,原子团的膨胀动力学过程的测量是获取强相互作用费米气体性质的重要手段之一.由于制备的原子团原子数少(~10~5)和温度高(~0.1T_F),此前的研究工作中强相互作用费米气体的膨胀过程通常仅能维持几毫秒.因此,本文首先制备出了大原子数(5×10~6)和极低温度(0.06(1)T_F)的费米超流.结合特殊的磁场设计,作者成功地观测到了长达30ms的费米超流体的类振荡膨胀过程.同时,作者测量了费米超流体的指数型状态方程,得到了准震荡频率与相互作用、温度的关系.该实验结果和方法将促进对费米超流诸多有趣现象的研究,如椭圆流、正常-超流相变和super-Efimov效应等.