# Josephson vortices in a long Josephson junction formed by phase twist in a polariton superfluid

## TL;DR

This paper demonstrates the optical control and observation of bosonic Josephson vortices in a polariton superfluid, revealing their role in superfluid behavior and excitations in quantum fluids of light.

## Contribution

It reports the first observation of bosonic Josephson vortices in a polariton condensate and explores their role in superfluid phase behavior.

## Key findings

- Imposed phase difference creates a $ ext{π}$-slippage and solitonic density depletion.
- Superfluid behavior is restored at higher densities via Josephson vortex nucleation.
- Results enhance understanding of excitations in macroscopic quantum systems.

## Abstract

Quantum fluids of light are an emerging platform for energy efficient signal processing, ultra-sensitive interferometry and quantum simulators at elevated temperatures. Here we demonstrate the optical control of the topological excitations induced in a large polariton condensate, realising the bosonic analog of a long Josephson junction and reporting the first observation of bosonic Josephson vortices. When a phase difference is imposed at the boundaries of the condensate, two extended regions become separated by a sharp $\pi$-slippage of the phase and a solitonic depletion of the density, forming an insulating barrier with a suppressed order parameter. The superfluid behavior, that is a smooth phase gradient across the system instead of the sharp phase jump, is recovered at higher polariton densities and it is mediated by the nucleation of Josephson vortices within the barrier. Our results contribute to the understanding of dissipation and stability of elementary excitations in macroscopic quantum systems.