How small a bit can be

ABSTRACT: High-density optical and magnetic storage using macroscopic properties of the re cording material, such as magnetization or reflectivity, are fast approaching th eir limits. Further progress requires manipulation of materials at the atomic le vel with the hope that a few atoms can be used to store a single ‘bit’ of informat ion. Such memories can be a million-times or more dense than their conventional optical or magnetic counterparts. Spectral hole-burning based memories provide s uch a storage where a group of atoms, to be precise a group of missing atoms, is used to store a ‘bit’. For the past quarter century spectral storage devices hav e not been realized; low densities, long storage times, and cryogenic temperatur es of operation have been the major obstacles towards a successful implementatio n. This has been due in large part to the lack of suitable materials and control on atomic scale processes that are initiated under intense laser excitation. By engineering the atomic as well as the bulk properties of the storage medium, hi gh-density storage approaching hundreds of terabits per square inch has been dem onstrated in my research group. These memories are in the form of thin film mult i-layer structures of II-VI materials where photo-ionization of Eu-impurities is responsible for the storage. They have all necessary characteristics for a prac tical device with one exception that they operate at low temperature. In this talk I will review the status of spectral storage, its future prospects, and the physical limits of this atomic scale storage.