Hefei,Science and Technology Daily,January 16(Reporter Wu Changfeng)The reporter learned from the University of Science and Technology of China on the 16th that Du Jiangfeng,Rongxing,et al.,the key laboratory of micro magnetic resonance of the Chinese Academy of Sciences,systematically studied the relationship between symmetry and high-order non Hermite singular point structures in a single spin system,and successfully observed a class of high-order non Hermite singular point structures.The relevant research results were published online on January 15th in Nature Nanotechnology.
  Non Hermitian physics pays special attention to a special type of degeneracy point-singularity-that exists in non Hermitian systems.Unlike degeneracy points in Hermitian systems,second-order or higher-order singular points have two or more eigenvalues and eigenstates simultaneously undergoing degeneracy.Due to the unique spectral properties near singular points,numerous novel physical phenomena unique to non Hermitian systems have emerged,making them of significant research value in fields such as quantum computing,precision measurement,and topological physics.The high-order singular point structure composed of high-order singular points,such as high-order singular lines and singular arcs,can exhibit richer topological properties.However,the observation of high-order singular points in quantum systems is no longer easy,and achieving high-order singular point structures is even more challenging.
  The research group is based on a single electron spin and nuclear spin composite system with a nitrogen vacancy color center in diamond,and based on its developed non Hermitian Hamiltonian implementation method,a non Hermitian system with both parity time symmetry and pseudochirality symmetry was achieved.Singular lines formed by a series of third-order singular points were successfully observed.The research group further elucidated the relationship between symmetry and higher-order non Hermitian singular structures.The experimental results indicate that when the Hamiltonian of the system has only parity time symmetry,only isolated third-order singular points can exist in the two-dimensional parameter space.When further removing the parity time symmetry of the system,there will be no third-order singular points in the two-dimensional parameter space.The experimental results demonstrate the important role of symmetry in studying high-order singular point structures.
  This research achievement lays the foundation for extensive non Hermitian physics research in multi-level systems.On the one hand,it helps to study new topological phases and topological invariants in multi-level non Hermitian systems;On the other hand,the eigenstate transformation based on high-order singular points and the enhancement of perturbation response are expected to have important applications in the fields of quantum control and quantum precision measurement.