Theories of dark energy generically introduce new light degrees of freedom to the gravitational sector. These degrees of freedom mediate a fifth force between matter particles, and there is currently no experimental evidence that such a force exists. A popular way around this problem is for the fifth force to dynamically weaken in certain environments. This idea, termed screening, was first proposed nearly 20 years ago, and has resulted in a great deal of theoretical and experimental activity since that time. In addition to several distinct screening mechanisms being identified, there are also a new generation of gravitational experiments currently being performed that are specifically designed to detect screened dark energy. In particular, atom interferometry has made great progress over the last three years towards detecting, or ruling out, one of the simplest and most popular models of screened dark energy, the chameleon.
