Collective Lamb Shift in Single-Photon Superradiance

All Together Now An atom, when excited, will typically decay with a characteristic decay time. An ensemble of atoms, collectively coupled together with just one of the atoms excited will conspire to decay much faster than the single atom case. This enhancement of light-matter interaction is known as superradiance. Röhlsberger et al. (p. 1248, published online 13 May; see the cover; see the Perspective by Scully and Svidzinsky) present the realization of an artificial superradiant system comprising resonant iron atoms embedded in a semiconductor cavity and excited by synchrotron radiation and report the signature collective Lamb shift expected from the cooperative interaction and enhanced decay rate. The availability of such a controlled system to look closer at this effect should shed light on its role in natural and complex light-harvesting systems, and possibly allow the production of more efficient solar cells. Superradiance is observed from an ensemble of iron atoms excited by synchrotron radiation. Superradiance, the cooperative spontaneous emission of photons from an ensemble of identical atoms, provides valuable insights into the many-body physics of photons and atoms. We show that an ensemble of resonant atoms embedded in the center of a planar cavity can be collectively excited by synchrotron radiation into a purely superradiant state. The collective coupling of the atoms via the radiation field leads to a substantial radiative shift of the transition energy, the collective Lamb shift. We simultaneously measured the temporal evolution of the superradiant decay and the collective Lamb shift of resonant 57Fe nuclei excited with 14.4–kilo–electron volt synchrotron radiation. Our experimental technique provides a simple method for spectroscopic analysis of the superradiant emission.