When a coherent superposition of Rydberg states is excited by a laser pulse, a Rydberg wave packet is created. These wave packets are supremely quantum mechanical objects. However, they can be constructed to display classical, nearly classical, or semiclassical behavior, and thus serve as a natural bridge between the microscopic and mesoscopic worlds. In addition, their comparative simplicity allows detailed studies of the fundamental interactions of light with matter.

The authors of this focus issue were invited to submit papers that reflect both the range of dynamical behavior exhibited by Rydberg wave packets, and the depth of understanding of them that is possible with current experiments and theory. In particular, the papers in this issue illustrate the possibility that emerging laser technology can be used not only to observe quantum behavior, but also to control it.

The paper by Noel and Stroud presents theory and experiment demonstrating the use of a train of phase-locked, ultrafast laser pulses to control the evolution of Rydberg wave packets. They show that adjusting the relative phase between the pulses allows a selective destruction of chosen eigenstates in the distribution. Raman, DeCamp and Bucksbaum demonstrate an alternative way to control Rydberg wave packets, using shaped THz pulses. They show that these pulses can selectively redistribute the eigenstate populations, causing resonant population transfer among chosen states. Campbell, Bensky and Jones report on the development of an instrument that allows monitoring of Rydberg wave packets with a single pair of laser fields. This device overcomes many of the problems inherent in traditional pump-probe techniques, and allows the design of an entirely new class of experiments. Alber and Eggers discuss the excitation of Rydberg wave packets with a fluctuating cw-laser field They show that the destruction of quantum interference by the fluctuations leads to a variety of novel effects, such as diffusion and stochastic ionization. Schafer and Krause point out that exciting a Stark manifold results in a complicated wave packet with a time-dependent dipole moment, and an attendant burst of coherent photon emission. They suggest that Stark wave packets might be used as a source of tunable THz radiation. Kalinski and Eberly investigate the possibility of controlling electrons captured in a special class of non-spreading wave packets called Trojan states. They show that applying an adiabatically chirped pulse to a Trojan wave packet results in selective compression or decompression of the packet. Finally, Lee, Farrelly and Uzer explore the creation of wave packets localized in orbits analogous to Bohr’s planetary orbits. They show that under appropriate conditions, an electron can be forced into a stable orbit akin to a charged particle in the ring of a giant planet.

I would like to thank the authors for their contributions, and for their willingness to participate in the new form of publication provided by Optics Express.

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