A Multimode Dial for Interatomic Interactions

I nteractions mediated by photons are ubiquitous in physical systems. For instance, the van der Waals interaction between atoms in free space—variants of which play a fundamental role in many physical, chemical, and biological processes—is mediated by photons of the electromagnetic vacuum between the atoms. Interestingly, while this interaction is weak and decays with interatomic separation when the atoms are in free space, its strength and range can be modified when the atoms are placed between the mirrors of an optical cavity. When such cavity quantum electrodynamics (QED) systems contain many atoms, they can be used to explore collective quantum phenomena. However, if the atoms dominantly couple to a single cavity light mode, as is usually the case, the photonmediated interatomic interactions are long-ranged, limiting the phenomena that can be explored. Benjamin Lev from Stanford University, California, and colleagues [1] have now engineered photon-mediated interactions in a cavity QED system that can be tuned from long range to short range. Such tunable-range interactions could be used to study collective quantum phenomena and phase transitions that are currently beyond the reach of other atomic systems and other cavity QED systems.