Spectrum of collective excitations of a quantum fluid of polaritons

We use a recently developed high-resolution coherent probe spectroscopy method to investigate the dispersion of collective excitations of a polaritonic quantum fluid. We measure the dispersion relation with high energy and wave-number resolution, which allows to determine the speed of sound in the fluid and to evidence the contribution of an excitonic reservoir. We report on the generation of collective excitations at negative energies, on the ghost branch of the dispersion curve. Precursors of dynamical instabilities are also identified. Our methods open the way to the precise study of quantum hydrodynamics of quantum fluids of light.

Automated summary

We use a high-resolution coherent probe spectroscopy method to study the dispersion of collective excitations in a polaritonic quantum fluid. By measuring the dispersion relation with high energy and wave-number resolution, we determine the speed of sound in the fluid and identify the contribution of an excitonic reservoir. We observe the generation of collective excitations at negative energies, on the ghost branch of the dispersion curve, and identify precursors of dynamical instabilities. Our methods enable precise study of quantum hydrodynamics in quantum fluids of light.