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# Josephson vortices induced by phase twisting a polariton superfluid

## Abstract

Quantum fluids of light are an emerging platform for energy-efficient signal processing, ultrasensitive interferometry and quantum simulators at elevated temperatures. Here we demonstrate all-optical control of the topological excitations in a large polariton condensate realizing the bosonic analogue of a long Josephson junction and inducing the nucleation of Josephson vortices. When a phase difference is imposed at the boundaries of the condensate, two extended regions become separated by a sharp phase jump of π radians and a solitonic depletion of the density, forming an insulating barrier with a suppressed order parameter. The superfluid behaviour—characterized by a smooth phase gradient across the system instead of the sharp phase jump—is recovered at higher polariton densities and 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 macroscale quantum systems.

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The raw experimental and numerical data used in this study are available from the corresponding author on reasonable request.

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## Acknowledgements

D.C., D.B. and D.S. acknowledge the ERC project POLAFLOW—Polariton condensates: from fundamental physics to quantum based devices (grant number 308136) and the ERC ‘ElecOpteR’ grant number 780757. N.B. and M.M. acknowlegde support from National Science Center grant numbers 2015/17/B/ST3/02273 and 2016/22/E/ST3/00045. The authors thank P. Cazzato for his constant help. Discussions with M. H. Szymańska are acknowledged. The work at Princeton University was funded by the Gordon and Betty Moore Foundation through the EPiQS initiative grant GBMF4420 and by the National Science Foundation MRSEC grant DMR 1420541.

## Author information

N.B. and M.M. developed the theoretical model and ran the numerical simulations. K.W. and L.N.P. grew the semiconductor microcavity sample used in the experiments. M.D.G., L.D. and G.G. provided technical support. D.C., D.S. and D.B. designed the experiment and analysed/discussed the results. All authors contributed to the discussion of the results and to the preparation of the manuscript.

### Competing interests

The authors declare no competing interests.

Correspondence to Dario Ballarini.

## Supplementary information

1. ### Supplementary Information

Supplementary notes and figures