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报告题目：Mixed-order symmetry-breaking quantum phase transition far from equilibrium
报告人：Prof. Stefano Chesi, Beijing Computational Science Research Center（北京计算科学研究中心）
报告摘要：The generalization of quantum phase transitions to non-equilibrium conditions raises a number of interesting questions. In particular, if and how out-of-equilibrium critical phenomena can be categorized into universality classes(in analogy with thermal equilibrium). Here we explore the non-equilibrium steady-state of a transverse magnetic field Ising chain coupled at its ends to magnetic thermal reservoirs, as schematically shown in Fig. 1(a). We generalize the phase diagram to non-equilibrium conditions (see Fig 1), obtained by applying a magnetization bias to the reservoirs . Upon increasing the bias, we observe a discontinuous jump of the magnetic order parameter that coincides with a divergent the correlation length (see Fig.2). In equilibrium, the first observation is a signature of a first-order transition while the second only arises for continuous (second-order) transitions. Thus, our findings show that out-of-equilibrium conditions allow for novel critical phenomena not possible at equilibrium. Moreover, for steady states with a non-vanishing conductance, the entanglement entropy at the zero temperature was found to have logarithmic corrections that differ from the well-known equilibrium case .
 T. O. Puel, S. Chesi, S. Kirchner, and P. Ribeiro, Phys. Rev. Lett. 122, 235701 (2019).
Stefano Chesi received his Ph.D. (2007) from Purdue University. In 2013 he became Research Scientist in RIKEN, Japan. He joined Beijing CSRC as a faculty in 2014, after being selected by the national Recruitment program 1000 Young Thousand Talents of China. His research area is Condensed Matter Theory, with strong interests in nanoscience, spin coherence, and Quantum Information.