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►【先进量子技术系列讲座第8期】

题目：Classical Simulation of Quantum Supremacy Circuits

时间：2020年7月9日（周四）10:00-11:00

报告人：陈建鑫（阿里巴巴集团）

摘要：It is believed that random quantum circuits are difficult to simulate classically. These have been used to demonstrate quantum supremacy: the execution of a task on a quantum computer that is infeasible for all classical computers. The task underlying the assertion of quantum supremacy by Arute {\em et al.} ({\em Nature}, {\bf 574}, 505--510(2019)) has been estimated to require Summit, the world's most powerful supercomputer today, at least 10,000 years. The same task was performed on their quantum processor Sycamore in only 200 seconds.
In this work, we present a classical simulation algorithm that, using a cluster on Alibaba Cloud with the same number of nodes and GPU specifications as Summit, can perform this task in 20 days. On smaller instances, we reduce the runtime from years to minutes, surpassing even Sycamore. The key ingredient is identifying and optimizing the ``stem'' of the computation: a sequence of pairwise tensor contractions that dominate the computational cost. This orders-of-magnitude reduction in classical simulation time, together with proposals for further significant improvements, indicate that achieving quantum supremacy may require a period of continuing quantum hardware improvements, without an unequivocal first demonstration.

报告人简介：Dr. Jianxin Chen is a Quantum Scientist of Alibaba Group and Head of Quantum Computer Systems of Alibaba Quantum Laboratory (AQL), a division of Alibaba Group's global research institute DAMO Academy. Jianxin received his Bachelor's and Ph.D. degrees from Tsinghua University, both in computer science. Prior to joining Alibaba, he was a postdoctoral fellow jointly with Department of Mathematics and Statistics, University of Guelph and Institute for Quantum Computing at University of Waterloo and then a Hartree postdoctoral fellow in the Joint Center for Quantum Information and Computer Science at University of Maryland. Jianxin's research focuses on classical simulation of quantum systems and scalable compilation of quantum circuits.