Long Coherence Times with Trapped Cold Atoms

Since the advent of laser cooling in the 80’s ultra cold neutral atoms have been extensively used for precision spectroscopic measurements, mostly under free falling conditions and low atomic density where the perturbations of trapping forces and atomic collisions are minimal. We review recent developments that exploit high density trapped ensembles of ultra cold atoms for precision spectroscopy and quantum memories. We show that the negative role of atomic collisions in limiting the attainable atomic coherence time can be suppressed and sometimes even inverted into a positive role.