# Anti-Parity-Time Symmetric Optical Four-Wave Mixing in Cold Atoms

## TL;DR

This paper demonstrates anti-PT symmetry in nonlinear optical four-wave mixing within cold atoms, revealing a phase transition between power oscillation and amplification without the need for gain-loss engineering.

## Contribution

It introduces anti-PT symmetry in a nonlinear optical system using cold atoms, distinct from previous gain-loss based PT systems.

## Key findings

- Observation of anti-PT phase transition
- Transition between power oscillation and amplification
- Negligible linear gain and loss in the system

## Abstract

Non-Hermitian optical systems with parity-time (PT) symmetry have recently revealed many intriguing prospects that outperform conservative structures. The prevous works are mostly rooted in complex arrangements with controlled gain-loss interplay. Here, we demonstrate anti-PT symmetry inherent in nonlinear optical interactions based upon forward optical four-wave mixing in a laser-cooled atomic ensemble with negligible linear gain and loss. We observe the pair of frequency modes undergo a nontrivial anti-PT phase transition between coherent power oscillation and optical parametric amplification in presence of a large phase mismatch.

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Source: https://tomesphere.com/paper/1901.06805