标题： 狄拉克奇异点的实验观测 显示英文标题

标题： Experimental observation of Dirac exceptional point

摘要： 能级简并，也称为奇异点（EPs），对于理解材料中的新兴现象以及为器件实现创新功能至关重要。 自EPs提出半个世纪以来，仅实验发现了两种类型的EPs，揭示了诸如狄拉克和外尔半金属等材料的有趣相。 这些发现展示了众多奇特的拓扑性质和新应用，例如单向能量传输。 在此，我们报告了利用金刚石中的氮空位中心观察到一种新型的EP，称为狄拉克EP。 在狄拉克EP处，两个本征值被测量为简并，并在其附近保持实数。 与狄拉克EP相关的这种奇特带结构拓扑使得在通过时能够保持对称性，并能够在非厄米系统中实现绝热演化。 我们通过量子态层析技术检查了两个本征态之间的简并，确认该简并点是一个狄拉克EP，而不是厄米简并。 我们对这种不同类型的EP的研究为非厄米系统中的动力学提供了新的视角，并可能在非厄米系统中的量子控制应用和EP拓扑性质的研究中具有价值。 显示英文摘要

摘要： The energy level degeneracies, also known as exceptional points (EPs), are crucial for comprehending emerging phenomena in materials and enabling innovative functionalities for devices. Since EPs were proposed over half a century age, only two types of EPs have been experimentally discovered, revealing intriguing phases of materials such as Dirac and Weyl semimetals. These discoveries have showcased numerous exotic topological properties and novel applications, such as unidirectional energy transfer. Here we report the observation of a novel type of EP, named the Dirac EP, utilizing a nitrogen-vacancy center in diamond. Two of the eigenvalues are measured to be degenerate at the Dirac EP and remain real in its vicinity. This exotic band topology associated with the Dirac EP enables the preservation of the symmetry when passing through, and makes it possible to achieve adiabatic evolution in non-Hermitian systems. We examined the degeneracy between the two eigenstates by quantum state tomography, confirming that the degenerate point is a Dirac EP rather than a Hermitian degeneracy. Our research of the distinct type of EP contributes a fresh perspective on dynamics in non-Hermitian systems and is potentially valuable for applications in quantum control in non-Hermitian systems and the study of the topological properties of EP.