  Vacuum quantum fluctuations near horizons are known to yield correlated
emission by the Hawking effect. We use a driven-dissipative quantum fluid of
microcavity polaritons as an analog model of a quantum field theory on a
black-hole spacetime and numerically calculate correlated emission. We show
that, in addition to the Hawking effect at the sonic horizon, quantum
fluctuations may result in a sizeable stationary excitation of a quasi-normal
mode of the field theory. Observable signatures of the excitation of the
quasi-normal mode are found in the spatial density fluctuations as well as in
the spectrum of Hawking emission. This suggests an intrinsic fluctuation-driven
mechanism leading to the quantum excitation of quasi-normal modes on black hole
spacetimes.
