Gravitational Decoherence

We discuss effects of loss of coherence in low energy quantum systems causedby or related to gravitation, referred to as gravitational decoherence. Theseeffects, resulting from random metric fluctuations, for instance, promise to beaccessible by relatively inexpensive table-top experiments, way before thescales where true quantum gravity effects become important. Therefore, they canprovide a first experimental view on gravity in the quantum regime. We willsurvey models of decoherence induced both by classical and quantumgravitational fluctuations; it will be manifest that a clear understanding ofgravitational decoherence is still lacking. Next we will review models wherequantum theory is modified, under the assumption that gravity causes thecollapse of the wave functions, when systems are large enough. These modelschallenge the quantum-gravity interplay, and can be tested experimentally. Inthe last part we have a look at the state of the art of experimental research.We will review efforts aiming at more and more accurate measurements of gravity(G and g) and ideas for measuring conventional and unconventional gravityeffects on nonrelativistic quantum systems.