High-Resolution Coherent Probe Spectroscopy of a Polariton Quantum Fluid

Characterizing elementary excitations in quantum fluids is essential to study their collective effects. We present an original angle-resolved coherent probe spectroscopy technique to study the dispersion of these excitation modes in a fluid of polaritons under resonant pumping. Thanks to the unprecedented spectral and spatial resolution, we observe directly the low-energy phononic behavior and detect the negative-energy modes, i.e., the ghost branch, of the dispersion relation. In addition, we reveal narrow spectral features precursory of dynamical instabilities due to the intrinsic out-of-equilibrium nature of the system. This technique provides the missing tool for the quantitative study of quantum hydrodynamics in polariton fluids.

Automated summary

In this study, we present an original angle-resolved coherent probe spectroscopy technique to characterize elementary excitations in polariton fluids. With unprecedented spectral and spatial resolution, we directly observe the low-energy phononic behavior and detect negative-energy modes, as well as reveal narrow spectral features precursory of dynamical instabilities due to the intrinsic out-of-equilibrium nature of the system.