Experimental Observation of Partial Parity-Time Symmetry and Its Phase Transition with a Laser-Driven Cesium Atomic Gas

TL;DR

This paper reports the first experimental observation of partial PT symmetry in a laser-driven cesium atomic gas, demonstrating phase transitions and precise exceptional point determination, advancing control of non-Hermitian optical systems.

Contribution

It introduces the first experimental realization of partial PT symmetry in atomic gases and develops a technique to locate the symmetry-breaking exceptional point.

Findings

Observation of partial PT symmetry in atomic gas

Detection of phase transition from unbroken to broken symmetry

Method for precise exceptional point measurement

Abstract

Realization and manipulation of parity-time (PT) symmetry in multidimensional systems are highly desirable for exploring nontrivial physics and uncovering exotic phenomena in non-Hermitian systems. Here, we report the first experimental observation of partial PT (pPT) symmetry in a cesium atomic gas coupled with laser fields, where a two-dimensional pPT-symmetric optical potential for probe laser beam is created. A transition of the pPT symmetry from an unbroken phase to a broken one is observed through changing the beam-waist ratio of the control and probe laser beams, and the domains of unbroken, broken, and non-pPT phases are also discriminated unambiguously. Moreover, we develop a technique to precisely determine the location of the exceptional point of the pPT symmetry breaking by measuring the asymmetry degree of the probe-beam intensity distribution. The findings reported here pave the way for controlling multidimensional laser beams in non-Hermitian systems via laser-induced atomic coherence, and have potential applications for designing new types of light amplifiers and attenuators