Observation of energy-difference conservation in optical domain

Date:
September 23, 2021
Source:
Pohang University of Science & Technology (POSTECH)
Summary:
A research team proposes an efficient experimental platform for non-
Hermitian physics research.



FULL STORY ==========================================================================
When optical gain or loss are precisely controlled using nanophotonics,
a new physical event called the non-Hermitian phenomenon can be observed, potentially the next-generation technology of optical signal control
and sensing. However, it is difficult to control the optical gain and
loss in optical experiments precisely.


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

The Hermitian-Hamiltonian operator has been used for a long time as a
basic operating principle of quantum physics, assuming that there is
no energy loss in a closed system. However, all physical systems in an
open system have energy loss, which is treated as a simple imperfection
and compensated by amplification.

However, the recently emerging field of non-Hermitian physics extends
the basic operating principle by giving gain and loss a new role other
than simple correction to incomplete systems. Demonstrating physical
phenomena different from those of the standard Hermitian-Hamiltonian
dynamics is attracting attention as the next generation signal and energy control technology.

Among the non-Hermitian physical systems, anti-parity-time (APT) symmetry systems consisting of balanced gain and loss can induce symmetry-breaking transitions that occur at an exceptional point, energy-difference
conservation, and synchronized power oscillations. However, optical energy-difference conservation and synchronized power oscillation have
not yet been observed due to the difficulty of balancing perfectly
optical gain and loss.

To this, the researchers produced an APT symmetry platform based on
nonlinear four-wave-mixing (FWM) using optical fibers widely used in
optical communication. Using optical fibers enabled a simple experimental device with an elongated interaction length with little energy loss,
which has been difficult to access even in nano-photonics due to the fabrication limitations.

Using the proposed method, the researchers observed synchronized
oscillations of optical intensity thanks to the long optical fibers
as well as symmetry- breaking transitions at an exceptional point. In
addition, using the low loss and nonlinearity of optical fibers, the energy-difference conservation -- a unique behavior of the APT symmetry
systems -- was observed for the first time in the optical domain.

"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." ========================================================================== Story Source: Materials provided by Pohang_University_of_Science_&_Technology_(POSTECH).

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Sebae Park, Dongjin Lee, Kyungdeuk Park, Heedeuk Shin, Youngsun
Choi, Jae
Woong Yoon. Optical Energy-Difference Conservation in a Synthetic
Anti- PT-Symmetric System. Physical Review Letters, 2021; 127 (8)
DOI: 10.1103/ PhysRevLett.127.083601 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210923115645.htm

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