In a first phase, we addressed the full characterisation of quantum fluids of light properties, including the observation of superfluid light and of turbulent regimes with the creation of topological excitations. In a second phase, we exploited the established playground to address the simulation of Black Holes in various geometries, to study phase transitions in driven-dissipative systems and to assess the potential of the photonic platforms to simulate strongly correlated systems.
1. Experimental observation and theoretical description of superfluid light
The characterisation of the superfluid behaviour of quantum fluids of light and the observation of quantum turbulence in several systems allowed measuring with an unprecedented resolution the spectrum of the collective excitations of driven dissipative quantum fluid of light. It allowed also to demonstrate that the stochastic evolution of the phase of a driven dissipative condensate follows the Kardar-Parisi-Zhang universlity class. This is an important breakthrough in the field as it demonstrates for the first time that quantum fluids of light can go beyond mean field physics and simulate systems whose evolution is governed by purely quantum effects such as quantum phase fluctuations in this specific case.
2. Simulation of unreachable systems, from condensed matter to astrophysics
The analogue quantum simulation of astrophysical and condensed matter systems was accompanied with studies of phase transitions unique to driven dissipative platforms. Experiments were prepared via theoretical studies, including numerical simulations of stochastic phenomena so as to enable the observation of predicted astrophysical effects (eg, Hawking radiation or superradiance). These also resulted in the discovery of new phenomena related to black hole horizons: analogue models, like black holes, have quasi-normal modes and calculations showed for the first time that these are excited by the zero-point fluctuations of the electromagnetic field. The general derivation of the result suggests that the same behaviour should be valid also for real black holes, due to the quantum fluctuation of the gravitational field. These setups also allowed demonstrating of single photon nonlinearity in polaritons, pushing quantum fluids of light deeply in the quantum regime and enabling the realization of fully programmable quantum logic gates in a fully scalable system.
3. Observation of turbulent regime with the generation of various topological excitations
On the one hand, numerical simulations led to the discovery of novel applications of photon fluids for the realisation of large-scale simulations of condensed matter models, and for universal computing applications. In particular, calculations of light propagation guided the implementation of a record size, fully scalable Ising machine. On the other hand, a new regime of propagation was discovered for polaritons, which stems from their dynamics out of equilibrium. This led to the development of all-optical methods to impring topological excitations of the fluid (soliton and vortex pairs) and to the observation of their controlled propagation over macroscopic distances. This control was also put to use to solve an optical maze, thus demonstrating the taming of the so-called snake instabilities, which inherently limit the excitation and propagation of topological excitations in quantum fluids.
