论文标题

量子准蒙特卡洛算法,用于长时间平衡的绿色功能

Quantum Quasi-Monte Carlo algorithm for out-of-equilibrium Green functions at long times

论文作者

Bertrand, Corentin, Bauernfeind, Daniel, Dumitrescu, Philipp T., Maček, Marjan, Waintal, Xavier, Parcollet, Olivier

论文摘要

我们扩展了最近开发的量子准蒙特卡洛(QQMC)方法,以在单个计算中获得绿色函数的全频率依赖性。 QQMC是一种通用方法,用于计算电子电子相互作用强度的高阶扰动膨胀。与常规的马尔可夫链蒙特卡洛采样相反,QQMC使用低静止序列来对所涉及的多维积分进行更均匀的采样,并且可以通过几个幅度来超过蒙特卡洛。 QQMC的核心概念是“模型函数”的先验构造,该函数近似于集成,并用于优化采样分布。在本文中,我们表明模型函数概念扩展到用于计算绿色功能的内核方法。我们说明了Anderson杂质模型的方法,并表明,在最佳情况下,Integrand评估$ n $的误差的比例是$ n $是$ \ sim 1/n^{0.86} $,并且与Monte Carlo缩放$ \ sim 1/n^{0.5} $相媲美。在使用基本的模型函数的同时,我们发现至少两个数量级对蒙特卡洛采样的系统改进。最后,我们将QQMC结果与用叉张量产品状态(FTPS)方法进行的计算进行了比较,这是一种最近开发的张量网络方法,用于解决杂质问题。在串联重新调整中,应用简单的padé近似值,我们发现QQMC匹配FTPS结果超出了扰动状态。

We extend the recently developed Quantum Quasi-Monte Carlo (QQMC) approach to obtain the full frequency dependence of Green functions in a single calculation. QQMC is a general approach for calculating high-order perturbative expansions in power of the electron-electron interaction strength. In contrast to conventional Markov chain Monte Carlo sampling, QQMC uses low-discrepancy sequences for a more uniform sampling of the multi-dimensional integrals involved and can potentially outperform Monte Carlo by several orders of magnitudes. A core concept of QQMC is the a priori construction of a "model function" that approximates the integrand and is used to optimize the sampling distribution. In this paper, we show that the model function concept extends to a kernel approach for the computation of Green functions. We illustrate the approach on the Anderson impurity model and show that the scaling of the error with the number of integrand evaluations $N$ is $\sim 1/N^{0.86}$ in the best cases, and comparable to Monte Carlo scaling $\sim 1/N^{0.5}$ in the worst cases. We find a systematic improvement over Monte Carlo sampling by at least two orders of magnitude while using a basic form of model function. Finally, we compare QQMC results with calculations performed with the Fork Tensor Product State (FTPS) method, a recently developed tensor network approach for solving impurity problems. Applying a simple Padé approximant for the series resummation, we find that QQMC matches the FTPS results beyond the perturbative regime.

扫码加入交流群

加入微信交流群

微信交流群二维码

扫码加入学术交流群,获取更多资源