Echo spectroscopy and quantum stability of trapped atoms

This work investigates the dephasing of ultra cold ⁸⁵Rb atoms trapped in an optical dipole trap and prepared in a coherent superposition of the two hyperfine ground states by interaction with a so-called π/2 micro wave (MW) pulse. The dephasing, measured as the Ramsey fringe contrast decay and related with the Loschmidt echo decay, can be reversed by stimulating a "coherence echo". The later is obtained by adding a population-inverting "p" pulse between the usual two π/2 pulses. Echo spectroscopy on atoms in a Gaussian beam red-detuned trap is performed and observed, for the proper trap parameters, a coherent signal, which for long times decays due to photon scattering, and has a time scale two orders of magnitude longer than the Ramsey decoherence times.