Decoherence of high-$\ell $ Rydberg wave packets by collisions and electrical noise

Quantum revivals in very-high-$n$ ($n\sim $300) high-$\ell $ Rydberg wave packets generated from parent $n$p states are used to examine decoherence induced by collisions and by the application of ``colored'' noise from a random pulse generator. In the absence of external perturbations, the high-$\ell $ wave packets maintain their coherence for periods $\sim $ 1 $\mu $s, i.e., for many hundreds of orbits. However, their coherence can be destroyed on sub-microsecond timescales by the presence of even small amounts of electrical noise at a rate that depends markedly on the spectral characteristics of the noise. In contrast, measurements over similar timescales with CO$_{2}$ target gas at densities of $\sim $ 10$^{11}$ cm$^{-3}$ provide no evidence of collisional dephasing.