The decay in the hyperfine coherence of optically trapped atoms due to interactions with the environment, is only partly suppressed by “echo” spectroscopy [M. F. Andersen et al. Phys. Rev. Lett. 90, 023001 (2003)], primarily due to dynamical (time-dependent) dephasing mechanisms. We demonstrate here an improved pulse sequence, for which the decay of coherence is reduced by a factor of $2.5$ beyond the reduction offered by the “echo” spectroscopy. This reduction occurs when each dark period in-between pulses is shorter than the time scale over which substantial dephasing develops. The coherence time is then limited by mixing to other vibrational levels in the trap and, to a lesser extent, the lifetime of the internal states of the atoms.

• Received 17 December 2003

DOI:https://doi.org/10.1103/PhysRevA.70.013405