title: Process tomography of dynamical decoupling in a dense cold atomic ensemble.
abstract: Atomic ensembles have many potential applications in quantum information science. Owing to collective enhancement, working with ensembles at high densities increases the efficiency of quantum operations, but at the same time also increases the collision rate and leads to decoherence. Here we report on experiments with optically trapped 87Rb atoms demonstrating a 20-fold increase of the coherence time when a dynamical decoupling sequence with more than 200 pi pulses is applied. Using quantum process tomography we demonstrate that a dense ensemble with an optical depth of 230 can be used as an atomic memory with coherence times exceeding 3 seconds.
authors.affiliation: Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Yoav
authors.initials: Y
authors.lastname: Sagi
authors.forename: Ido
authors.initials: I
authors.lastname: Almog
authors.forename: Nir
authors.initials: N
authors.lastname: Davidson