Photo credit: phys.org
Exploring the Groundbreaking Discovery of Dirac Exceptional Points
Exceptional points (EPs) represent a fascinating phenomenon in non-Hermitian systems, characterized by unique energy-level degeneracies. Although the concept was introduced over a century ago, empirical observations have largely been limited to two specific types of EPs. These have paved the way for unusual phases of matter, particularly in materials like Dirac and Weyl semimetals.
Researchers from the University of Science and Technology of China have recently made strides toward the experimental identification of a novel class of EPs, termed Dirac EPs. Their findings, detailed in a publication in *Physical Review Letters*, promise to shed light on non-Hermitian dynamics and set the stage for innovative methods to manipulate quantum systems.
“Our motivation originated from a previous theoretical study that postulated the existence of Dirac EPs,” explained Xing Rong, a lead author of the study. “We recognized that this exceptional type differs fundamentally from all EPs previously observed in experiments. Our objective was to translate this theoretical insight into a tangible experiment.”
Dirac EPs are thought to merge concepts from Dirac points in Hermitian systems with the characteristics of EPs unique to non-Hermitian systems. The researchers aimed to construct and identify these degeneracies using nitrogen-vacancy defects in diamonds—nanoscale quantum systems within a solid-state framework.
“We synthesized a non-Hermitian Hamiltonian featuring Dirac EPs by incorporating a spin-squared operator into a three-level non-Hermitian system,” Rong elaborated. “Utilizing our established dilation method, we experimentally implemented this Hamiltonian with nitrogen-vacancy defects in diamond. We confirmed the existence of Dirac EPs by detecting real eigenvalues in proximity to them and the degeneracy of eigenstates at these points.”
The successful identification of Dirac EPs, which introduces Hermitian-like symmetry into non-Hermitian frameworks, may catalyze further experimental initiatives in this field. Such work is likely to deepen our understanding of these new energy-level degeneracies, potentially leading to breakthrough methodologies for controlling quantum states.
“The Dirac EP reveals a unique real-valued eigenvalue spectrum, challenging the traditional notion that EPs invariably come with complex eigenvalues,” noted Rong. “This attribute fosters adiabatic evolution in non-Hermitian contexts and mitigates dissipative challenges, presenting significant opportunities for applications in topological physics and quantum control strategies.”
Rong and his team are optimistic that their research will ignite further developments in non-Hermitian and quantum physics. They believe that the experimental confirmation of Dirac EPs could open new pathways for quantum physicists and engineers, enhancing their capability to manipulate various advanced quantum technologies, which include sensors and quantum computing systems.
“Dirac EPs can prevent non-adiabatic transitions typically associated with conventional EPs, making it feasible to study complex geometric phases experimentally,” Rong added. “The successful identification of Dirac EPs in our work paves the way for exploring geometric phases in non-Hermitian systems in future experiments.”
More information:
Yang Wu et al, Experimental Observation of Dirac Exceptional Points, *Physical Review Letters* (2025). DOI: 10.1103/PhysRevLett.134.153601. On arXiv: DOI: 10.48550/arxiv.2503.08436
Source
phys.org