Physics. Interfacing atoms and light--the smaller the stronger.

1175 PERSPECTIVES M ost of us use the Internet to exchange information in everyday life. The ever-increasing rate at which Internet connections transmit data requires faster and faster conversion of local information into signals that can be easily transmitted over long distances. For example , the information sent by your computer is converted from electronic signals into optical signals, which are then sent through a network of optical fi bers. Without the reliable and high-speed conversion of information from electronic to optical form, modern communication would not be possible. With the emergence of quantum technologies, most notably quantum information technology , the way we communicate is about to change fundamentally. On page 1202 of this issue, Thompson et al. (1) describe a system that has the potential to become an interface between atoms and optical signals and provide local information storage and transmission in the quantum domain. In recent years, the processing of quantum information, where quantum-mechanical effects are used to potentially speed up computations, has been demonstrated in several systems (2– 6). With these achievements, the question of long-distance communication in the quantum realm arises (7). As in the classical communication domain, a crucial building block consists of converters that can transform quantum information from one form into another, so-called quantum hybrid systems or quantum interfaces. Currently, the most successful implementation for such quantum interfaces for long-distance quantum communication is cavity quantum elec-trodynamics, where atoms interact with light in a cavity. Recently, the transfer of information between atomic states by single light particles (photons) or the entanglement of their states has been demonstrated (8– 10). However , a technological challenge is still the fast, effi cient, and faithful transfer of information between atoms and photons. To enhance the interaction between photons and atoms, both need to be tightly confi ned at the same location , and trapped for a suffi ciently long time to allow the information transfer. The smaller the space in which both are confi ned, the stronger the interaction is, and the faster the interface operates. In 1999, Ye et al. (11) trapped atoms in an optical cavity and demonstrated the control of the interaction between atoms and single photons. This technique was later used by Stute et al. (8) to demonstrate a quantum network. In a quest to increase the coupling strength between atoms and pho-tons, Colombe et al. (12) combined a cavity, formed by …