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The numerical sign problem is known as the problem of evaluating the high oscillatory functions by numerical method. In many physics problems involving complex valued actions, the sign problem prevents people from using the conventional Monte Carlo method to numerically evaluate the observables. Many recent progresses suggest that the Picard-Lefschetz theory can cure the sign problem. In my work, an algorithm combining the Lefschetz thimble method and Differential Evolution Adaptive Metropolis (DREAM) algorithm is proposed to compute the expectation value of any observable in any system suffering from the sign problem. In particular, this algorithm is applied to compute the spin foam propagator, which is a 2-point correlation function introduce in the Loop Quantum Gravity (LQG) theory, and we hope this algorithm can have broader applications in lattice QCD, Non-Hermitian system, etc.
Zichang obtained his bachelor from Beijing Normal university. He then moved to Aix-Marseille University in France for his master and Florida Atlantic University in the US for his PhD. After that he came back to China and has been working as a postdoctoral researcher at Fudan university. His research interest focus on loop quantum gravity, quantum computing and numerical computation.