The study of wave chaos within optical microcavities provides a beautiful avenue to bridge classical and quantum physics. It falls into the branch of quantum chaos, which holds prospective potential for advancing technology by integrating these two fundamental philosophies of physics. The peculiar and unpredictable behavior observed in chaotic microcavities mirrors other chaotic systems, including perturbed atoms and quantum dots. Therefore, by exploring the topological properties of optical modes in microcavities, we can gain valuable insights into the behavior of various chaotic systems, deepening our understanding of nature's elegance.

In the study published in Light: Science & Application, a collaborative team led by Dr. YI Chang-Hwan from the Center for Theoretical Physics of Complex Systems within the Institute for Basic Science, Republic of Korea, Prof. PARK Hee Chul from Pukyong National University, Republic of Korea, and Prof. PARK Moon Jip from Hanyang University, Republic of Korea, achieved significant breakthroughs in wave chaos research within the realm of quantum chaos.

The team's study focused on dynamical localization transitions in a periodic array of chaotic cavities, specifically exploring the behavior of light wave modes within deformed optical microcavities coupled to crystalline momentum. The authors coined a new term for this phenomenon, naming it “cavity-momentum locking”.

Their investigations shed light on the quantum scar phenomenon and its transmutation, which occur within the microcavities embedded in photonic crystals. The quantum scar is an intriguing quantum eigenstate, which appears as a consequence of wave interference, exhibiting enhanced probability density around unstable periodic orbits that correspond to unstable fixed points in a classically chaotic system. Existence of these structures challenges the stability principles in traditional classical mechanics. By manipulating the crystalline momentum, the team demonstrated that these quantum scar states can be precisely controlled.

This discovery not only provides a deeper understanding of the intricate nature of wave chaos but also opens up exciting possibilities for utilizing the intrinsic wave properties of chaotic states to promote Berry curvature-induced transport phenomena. The authors underscore the groundbreaking nature of this research, highlighting its potential to manipulate the light wave behaviors over periodically structured microcavities. This has profound implications for quantum information, communication, and the development of optoelectronic devices.

Importantly, the ability to control quantum scar states within optical resonators composing photonic crystals unlocks the potential for various quantum technologies, including extreme-resolution quantum sensing. Additionally, the research findings contribute to advancements in frameworks of quantum chaos studies, expanding it to the crystal momentum-associated quantum chaos in photonic crystals.

Figure 1. The quantum scar state in a chaotic optical microcavity embedded in a photonic crystal can be engineered employing the “cavity-momentum locking” phenomenon. It is discovered that when the chaotic cavities are periodically arranged, the new degree of freedom, the “Bloch Crystalline momentum,” brings about the emerging transmutation of the quantum scar states. This allows us to devise novel control schemes of light integrating the intra-cavity chaos and the crystalline momentum of the cavity array.