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I will talk about two recent surprises in the quantum Monte Carlo (QMC) simulation of quantum phase transitions. Surprise one is the solution of a thirty years old sign problem by Huffman and Chandrasekharan. It enables us to study the fermionic quantum critical point of spinless Dirac fermions using unbiased continuous-time QMC simulations. Compatible results are also obtained from infinite projected entangled-pair states calculations. I will compare the numerical results with predictions of the Gross-Neveu theory and discuss their physical implications. Surprise two is a generic, efficient and elegant approach to compute fidelity susceptibility of correlated fermions, bosons, and quantum spin systems in modern QMC methods. It can be used to detect quantum phase transitions without any prior knowledge of the local order parameter. Using it I will shed light on the hypothetical spin-liquid phase in the Hubbard model on honeycomb lattice.

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Lei Wang, ETH Zurich
Seminar Room TP 0.03
Contact: Simon Trebst