Revue en français sur le site de l’Institut de Physique du CNRS : https://www.inp.cnrs.fr/fr/cnrsinfo/quand-la-lumiere-coherente-revele-un-comportement-universel

Nature’s News and Views 24 August 2022 : A new phase for universal growth of interfaces by Sebastian Diehl

What links the spread of a forest fire and the condensed state of quasiparticles called exciton–polaritons — tiny hybrid objects made of light and matter that are found in semi­conductors ? Fontaine et al. answer this question on page 687 with experiments showing that a property of the wave-like nature of the quasiparticles in the condensate behaves just like an interface : it is governed by a mathematical expression, known as the Kardar–Parisi–Zhang (KPZ) equation , that describes interfaces ranging from wildfire fronts to the growth of a bacterial colony. The results suggest that a versatile quantum-optical platform could be used to explore this far-reaching model of non-equilibrium statistical mechanics in a controlled way.[...]

more on https://www.nature.com/articles/d41586-022-02117-9

Article published page 687

[...] Revealing universal behaviours is a hallmark of statistical physics. Phenomena such as the stochastic growth of crystalline surfaces and of interfaces in bacterial colonies, and spin transport in quantum magnets all belong to the same universality class, despite the great plurality of physical mechanisms they involve at the microscopic level. Morespecifically, in all these systems, space–time correlations show power-law scalings characterized by universal critical exponents. This universality stems from a common underlying effective dynamics governed by the nonlinear stochastic Kardar–Parisi–Zhang (KPZ) equation. Recent theoretical works have suggested that this dynamics also emerges in the phase of out-of-equilibrium systems showing macroscopic spontaneous coherence. Here we experimentally demonstrate that the evolution of the phase in a driven-dissipative one-dimensional polariton condensate falls in the KPZ universality class. Our demonstration relies on a direct measurement of KPZ space–time scaling laws, combined with a theoretical analysis that reveals other key signatures of this universality class. Our results highlight fundamental physical differences between
out-of-equilibrium condensates and their equilibrium counterparts, and open a paradigm for exploring universal behaviours in driven open quantum system. [...]

more on https://www.nature.com/articles/s41586-022-05001-8 or https://doi.org/10.1038/s41586-022-05001-8

arXiv:2112.09550

In the article’s references :

• 13 : Squizzato, D., Canet, L. & Minguzzi, A. Kardar–Parisi–Zhang universality in the phase distributions of one-dimensional exciton–polaritons. Phys. Rev. B 97, 195453 (2018).
  http://arxiv.org/pdf/1712.03709
  https://doi.org/10.1103%2FPhysRevB.97.195453

• 16 : Deligiannis, K., Squizzato, D., Minguzzi, A. & Canet, L. Accessing Kardar–Parisi–Zhang universality sub-classes with exciton polaritons. Europhys. Lett. 132, 67004 (2021).
  http://arxiv.org/pdf/2010.06435
  https://doi.org/10.1209%2F0295-5075%2F132%2F67004