We propose that a broad class of excited-state quantum phase transitions (ESQPTs) gives rise to two different excited-state quantum phases. These phases are identified by means of an operator, $\hat{\mathcal{C}}$, which is a constant of motion only in one of them. Hence, the ESQPT critical energy splits the spectrum into one phase where the equilibirium expectation values of physical observables crucially depend on this constant of motion, and another phase where the energy is the only relevant thermodynamic magnitude. The trademark feature of this operator is that it has two different eigenvalues, $\pm1$, and therefore it acts as a discrete symmetry in the first of these two phases. This scenario is observed in systems with and without an additional discrete symmetry; in the first case, $\hat{\mathcal{C}}$ explains the change from degenerate doublets to non-degenerate eigenlevels upon crossing the critical line. We present stringent numerical evidence in the Rabi and Dicke models, suggesting that this result is exact in the thermodynamic limit, with finite-size corrections that decrease as a power-law.
Qumode-Based Variational Quantum Eigensolver for Molecular Excited States
Yale University（耶鲁大学）；University of Connecticut（康涅狄格大学）；Mirion Technologies (Canberra) Inc.（米尔尼昂技术（堪培拉）公司）；The University of Chicago（芝加哥大学）；Yale Quantum Institute, Yale University（耶鲁大学量子研究所）
Quantum self-consistent equation-of-motion method for computing molecular excitation energies, ionization potentials, and electron affinities on a quantum computer
Ultrafast spin-flip dynamics in transition metal complexes triggered by soft X-ray light
阿秒物理学的最新进展提供了在其内在时间尺度上的价电子和芯电子的相关运动的访问。对于价激发，与电子自旋相关的过程通常由核运动驱动。对于核心激发态，其中核心空穴具有非零角动量，自旋轨道耦合足够强以在短得多的时间尺度上驱动自旋翻转。在这里，前所未有的短自旋交叉驱动的自旋-轨道耦合证明了L-边缘（2 p $\rightarrow$ 3d）激发态的原型Fe（II）配合物。它发生在一个时间尺度上，这是快于核心空穴寿命约4~fs。对这些现象的详细分析将
