WRITING THE WORD "OPTICS" ON A SINGLE ATOM is possible, scientists have shown, demonstrating the huge information capacity that exists even in an individual hydrogen atom. The trick is to sculpt the electron cloud surrounding an atom into the letters of this word. Shining an ultrashort UV laser pulse and lower-frequency electromagnetic waves on an atom can send one of its electrons to a high-lying "Rydberg state," in which it no longer exists as a cloud of charge enshrouding the nucleus but instead becomes a "wavepacket" that circles the atomic nucleus like a planet around a sun (Update 234). Applying a series of pulses can create a set of wavepackets that combine with each other like water waves and cancel each other out at specific places to form patterns around the atom, such as the word "optics," in which points on each letter correspond to possible places for finding the electron after measurement. Although neither this feat, nor the act of accurately measuring such spatial patterns, can yet be achieved technologically, Carlos Stroud of the University of Rochester (716-275-2598) and Michael Noel of the University of Virginia (804-924-6599) point out that an electron in an n=50 Rydberg state (49 energy levels higher than the lowest state) has 2,500 possible states of angular momentum, and have shown that the states can be combined in many ways, such as to form this word. (Optics & Photonics News, April 1999; See figure at Physics News Graphics.)