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.

An optical time-domain reflectometer (OTDR) is a device that is used to precisely identify problems in a communication network’s optical fiber link. Its job is to generate and transmit a succession of high-speed optical pluses throughout the fiber. An OTDR simply sends a pulse across a fiber to check for flaws or errors. OTDRs are also used to ensure the smooth operation of countrywide telephone exchanges and poles within the network.

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.

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. In an open system, however, all physical systems suffer energy loss, which is considered as a basic flaw and rectified by amplification.

This study provides an efficient experimental framework for research on non-Hermitian physics.

Professor Heedeuk Shin

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.

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 will serve as a stepping stone for multidisciplinary study in areas such as materials development and quantum information technology.”

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