An Experimental Platform for Non-Hermitian Physics Study has been Proposed by a Research Group

When optical gain or loss is accurately regulated with nanophotonics, a novel physical occurrence known as the non-Hermitian phenomena may be detected, possibly paving the way for next-generation optical signal management and sensing technologies. However, accurate control of optical gain and loss in optical experiments is challenging.

The study of the behavior of light on the nanoscale scale, as well as the interaction of nanometer-scale objects with light, is known as nanophotonics or nano-optics. Optics, optical engineering, electrical engineering, and nanotechnology are all branches of this field. It frequently incorporates dielectric structures, such as nanoantennas or metallic components, that use surface plasmon polaritons to transport and concentrate light.

Professor Heedeuk Shin of POSTECH’s Department of Physics, in collaboration with Professor Jae Woong Yoon of Hanyang University’s Department of Physics, proposed an easy-to-use approach to non-Hermitian optical research and observed energy-difference conservation in the optical domain for the first time.

Example of non-Hermitian phenomenon

The Hermitian-Hamiltonian operator, which assumes no energy loss in a closed system, has been employed as a basic operational principle of quantum physics for a long time. Researchers in nanophotonics work on a wide range of projects, from biology to electrical engineering. In an open system, however, all physical systems suffer energy loss, which is considered as a basic flaw and rectified by amplification.

The newly developing discipline of non-Hermitian physics, on the other hand, expands the basic operating principle by giving gain and loss a new role other than simple incomplete system rectification. As the next generation signal and energy control technology, demonstrating physical phenomena other than those of ordinary Hermitian-Hamiltonian dynamics is gaining traction.

Nanophotonics has also been linked to the controlled and on-demand release of anti-cancer therapeutics such as adriamycin from nanoporous optical antennas to target triple-negative breast cancer, as well as mitigating exocytosis anti-cancer drug resistance mechanisms and avoiding toxicity to normal systemic tissues and cells.

The Hamiltonian in quantum mechanics supplies a system’s energy levels via its eigenvalues, as well as the system’s temporal development, which is regulated by the time-dependent Schrödinger equation. The study of PT – symmetric Hamiltonians is a common source of interest in non-hermitian systems.

Anti-parity-time (APT) symmetry systems with balanced gain and loss can cause symmetry-breaking transitions at an exceptional point, energy-difference conservation, and synchronized power oscillations, among other non-Hermitian physical systems. However, due to the difficulties of completely balancing optical gain and loss, optical energy-difference conservation and synchronized power oscillation have yet to be seen.

The researchers achieved this by developing an APT symmetry platform based on nonlinear four-wave mixing (FWM) and optical fibers commonly utilized in optical communication. Due to manufacturing difficulties, using optical fibers enabled a simple experimental device with an expanded interaction length and negligible energy loss, which has proven difficult to reach even in nano-photonics.

The researchers observed synchronized optical intensity oscillations owing to the lengthy optical fibers, as well as symmetry-breaking transitions at an unusual location, using the suggested approach. In addition, the energy-difference conservation a unique behavior of the APT symmetry systems was seen for the first time in the optical domain, thanks to the low loss and nonlinearity of optical fibers.

“This study provides an efficient experimental framework for research on non-Hermitian physics,” explained Professor Heedeuk Shin of POSTECH. “It will contribute to higher-level non-Hermitian research and become an important stepping stone for interdisciplinary research including materials development and quantum information science.”