Analogue cosmological particle creation in an ultracold quantum fluid of light

The rapid expansion of the early universe resulted in the spontaneous production of cosmological particles, some of which are observable today in the cosmic microwave background anisotropy. We present our observation of the spontaneous creation of analogue cosmological particles in the laboratory, using a quenched 3-dimensional quantum fluid of light.

We observe acoustic peaks in the density power spectrum, in close quantitative agreement with the quantum-field theoretical prediction. We find that the long-wavelength particles provide a window to early times. This work introduces the quantum fluid of light, as cold as an atomic Bose-Einstein condensate.