  Recent theoretical advances predict the existence, deep into the glass phase,
of a novel phase transition, the so-called Gardner transition. This transition
is associated with the emergence of a complex free energy landscape composed of
many marginally stable sub-basins within a glass metabasin. In this study, we
explore several methods to detect numerically the Gardner transition in a
simple structural glass former, the infinite-range Mari-Kurchan model. The
transition point is robustly located from three independent approaches: (i) the
divergence of the characteristic relaxation time, (ii) the divergence of the
caging susceptibility, and (iii) the abnormal tail in the probability
distribution function of cage order parameters. We show that the numerical
results are fully consistent with the theoretical expectation. The methods we
propose may also be generalized to more realistic numerical models as well as
to experimental systems.
