Quantum phase retrieval of a Rydberg wave packet using a half-cycle   pulse
  A terahertz half-cycle pulse was used to retrieve information stored as quantum phase in an $N$-state Rydberg atom data register. The register was prepared as a wave packet with one state phase-reversed from the others (the "marked bit"). A half-cycle pulse then drove a significant portion of the electron probability into the flipped state via multimode interference. 
J. Ahn, D. N. Hutchinson, C. Rangan, and P. H. Bucksbaum