PT Symmetry of a Square-Wave Modulated Two-Level System  

作　　者：Liwei Duan Yan-Zhi Wang Qing-Hu Chen 段立伟;汪延志;陈庆虎(Department of Physics and Zhejiang Province Key Laboratory of Quantum Technology and Device,Zhejiang University,Hangzhou 310027,China;Collaborative Innovation Center of Advanced Microstructures,Nanjing University,Nanjing 210093,China)

机构地区：[1]Department of Physics and Zhejiang Province Key Laboratory of Quantum Technology and Device,Zhejiang University,Hangzhou 310027,China [2]Collaborative Innovation Center of Advanced Microstructures,Nanjing University,Nanjing 210093,China

出　　处：《Chinese Physics Letters》2020年第8期36-42,共7页中国物理快报（英文版）

基　　金：Supported by the National Natural Science Foundation of China(Grant Nos.11674285 and 11834005);the National Key Research and Development Program of China(Grant No.2017YFA0303002).

摘　　要：We study a non-Hermitian two-level system with square-wave modulated dissipation and coupling.Based on the Floquet theory,we achieve an effective Hamiltonian from which the boundaries of the PT diagram are captured exactly.Two kinds of PT symmetry broken phases are found,whose effective Hamiltonians differ by a constant ω/2.For the time-periodic dissipation,a vanishingly small dissipation strength can lead to the PT symmetry breaking in the (2k-1)-photon resonance(△=(2k-1)ω),with k=1,2,3…It is worth noting that such a phenomenon can also happen in 2k-photon resonance(△=2kω),as long as the dissipation strengths or the driving times are imbalanced,namely γo≠-γ1orT0≠T1.For the time-periodic coupling,the weak dissipation induced$\mathcal{PT}$symmetry breaking occurs at △eff=kω,where △eff=(△0T0+△1 T1)/T.In the high frequency limit,the phase boundary is given by a simple relation γeff=±△eff.

关 键 词：DISSIPATION SYMMETRY BREAKING 

分 类 号：O413[理学—理论物理]