  The large density of gluons, which is present shortly after a nuclear
collision at very high energies, can lead to the formation of a condensate. We
identify a gauge-invariant order parameter for condensation based on elementary
non-perturbative excitations of the plasma, which are described by spatial
Wilson loops. Using real-time lattice simulations, we demonstrate that a
self-similar transport process towards low momenta builds up a macroscopic zero
mode. Our findings reveal intriguing similarities to recent discoveries of
condensation phenomena out of equilibrium in table-top experiments with
ultracold Bose gases.
