  Space--time can be understood as some kind of space--time foam of fluctuating
bubbles or loops which are expected to be an outcome of a theory of quantum
gravity. One recently discussed model for this kind of space--time fluctuations
is the holographic principle which allows to deduce the structure of these
fluctuations. We review and discuss two scenarios which rely on the holographic
principle leading to holographic noise. One scenario leads to fluctuations of
the space--time metric affecting the dynamics of quantum systems: (i) an
apparent violation of the equivalence principle, (ii) a modification of the
spreading of wave packets, and (iii) a loss of quantum coherence. All these
effects can be tested with cold atoms. These tests would supplement
measurements of a so called ``mystery noise'' at the gravitational wave
detector GEO600 which was recently speculated to have its origin in holographic
noise.
