报告一
【报告题目】：Quantum phase transitions of non-equilibrium spin systems
【报告人】：Stefano Chesi研究员（stefano.chesi@csrc.ac.cn），北京计算科学中心
【报告时间】：2024-10-11，09:00-
【报告地点】：29-414
【报告摘要】：Non equilibrium conditions enable a richer variety of critical phenomena and, in some cases, induce critical behaviors not permitted in equilibrium. In this talk I will give an overview of our recent work in this area. I first discuss a simple driven-dissipative setup composed by a single spin strongly coupled to a damped cavity mode, where photon decay induces non-trivial mixtures of superradiant and normal solutions [1]. A more challenging example is a 2D transverse Ising model with spin relaxation, where we have extended the cluster mean-field approach to extract critical exponents beyond mean-field, based on the coherent anomaly method [2]. Biased 1D chains are another interesting example of non-equilibrium systems. For a 1D transverse Ising model, we show that a finite magnetic bias can realize an exotic mixed-order phase transition, with a jump in magnetization accompanied by a diverging correlation length [3]. Finally, for localized spins interacting with 1D itinerant electrons, we have analyzed the effects of a voltage bias on the equilibrium spiral state. We find that at small bias a rigidly rotating magnetic state is established, which transitions to quasi-periodic and chaotic evolution at larger values of the applied voltage [4]. These dynamical states can realize electrically-driven transport of spin polarization and are of significant interest for topological superconductivity based on the spiral phase.
[1] J. Li, R. Fazio, Y.-D. Wang, and S. Chesi, to appear in Phys. Rev. Res. (2024)
[2] J. Jin, et al., Phys. Rev. B 104, 214301 (2021)
[3] T. O. Puel, Stefano Chesi, S. Kirchner, and P. Ribeiro, Phys. Rev. Lett. 122, 235701 (2019)
[4] X. Han, P. Ribeiro, S. Chesi, in preparation.
【报告人简介】：
08/2020 - present, Associate Professor, Beijing CSRC, China.
05/2014 - 08/2020, Assistant Professor, Beijing CSRC, China.
05/2013 - 05/2014, Research Scientist, RIKEN, Japan.
01/2011 - 04/2013, Postdoc, McGill University, Canada.
07/2007 - 12/2010, Postdoc, University of Basel, Switzerland.
Education
2007, Ph.D. in Condensed Matter Theory, Purdue University, USA.
2002, Laurea in Fisica (M.S.), University of Pisa and Scuola Normale Superiore, Italy.
报告二
【报告题目】：Reservoir engineering in Cavity Optomechanical systems
【报告人】：王颖丹研究员，中科院物理所
【报告时间】：2024-10-11，10:00-
【报告地点】：29-414
【报告摘要】：Cavity Optomechanical systems have attracted considerable interest in quantum information, quantum metrology, as well as fundamental physics. They are driven-dissipative systems and provide ideal platforms to implement reservoir engineering. In our past work, we have shown that strong steady-state entanglement can be achieved in a three-mode optomechanical system, or other parametrically coupled bosonic system, by effectively laser cooling a delocalized Bogoliubov mode. Our recent research shows that reservoir engineering can also help with other quantum protocols, such as the generation of strong squeezing and entanglement in the unresolved sideband regime, as well as realizing the antibunching and phononic Fock states with weak nonlinearity under thermal noise.
【报告人简介】：王颖丹，2001年毕业于华中师范大学物理系，获学士学位。2005年于中国科学院理论物理研究所获博士学位。2005年7月先后在日本电信电话公司（NTT）、瑞士Basel大学和加拿大McGill大学从事博士后研究工作。2013年5月在日本理化学研究所担任研究科学家。2014年5月回国工作。目前主要的研究兴趣为基于固态量子体系的量子态操控，特别是超导约瑟夫森结系统和光力学系统中的量子耗散和量子纠缠等问题。
