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"Quantifying Symmetry and Its Breaking in Quantum Systems"

Dr. Chang-Pu Sun
Beijing Computational Science Research Center
Beijing 100084, China


Symmetry is a theme of modern physics, which plays a crucial role in the understanding of fundamental interactions of the microscopic world as well as the emergence of macroscopic orders. It is conventionally described only in a contrariety manner that the system is either completely symmetric or completely asymmetric. Although this conventional approach has succeed in classifying the spectrum structure and even various phases of matters, it is not natural for us be- cause there is not a room for the intermediate circumstance, namely, a continuous measure of symmetry has not been found. Now using group theoretical approach to overcome this dichotomous problem, we introduce the degree of symmetry (DoS) as a non-negative continuous number ranging from zero to unity. DoS is defined through an average of the fidelity deviations of Hamiltonian or quantum state over its transformation group G, and thus is computable by making use of the completeness relations of the irreducible representations of G. The monotonicity of DoS can effectively probe the extended group for accidental degeneracy while its multi-valued natures characterize some (spontaneous) symmetry breaking.

Reference : Commun. Theor. Phys. 65 (2016) 423433

About Speaker

Professor Chang-Pu Sun, a theoretical physicist, currently is a chair professor at Beijing Computational Science Research Center (CSRC), and the Dean of Graduate School of the Chinese Academy of Engineering Physics (CAEP). He obtained his PhD in 1992 at the Chern Institute of Mathematics. He is also an Academician of CAS in 2009, and a Fellow of TWAS (the World Academy of Sciences) in 2011. His research interests include probing mathematical structures behind the dynamics of quantum systems, such as quantum groups related to the Yang- Baxter equation, Berry geometric phase related to general gauge symmetry and finite-size thermodynamic systems far off equilibrium. He currently studies the fundamental aspects of quantum mechanics, e.g., open quantum system approaches to quantum measurement and decoherence, and quantum statistical thermodynamics. His researches are partially oriented to future quantum technologies, such as quantum information processing, quantum coherent devices for Bio-Compass and also the new generation of energy based on the artificial photosynthesis with quantum effects.

Tuesday, May 10, 2016
IQSE 578, 12:30 Noon
Mitchell Physics Building

Institute for Quantum Science and Engineering
Texas A&M University

(Pizza, salad, and soda to be served at 12:00 noon)