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The Lamb Shift—Yesterday, Today, and Tomorrow

发布者： admin 发布时间：2010-06-06
　　

Science 4 June 2010:
Vol. 328. no. 5983, pp. 1239 - 1241
DOI: 10.1126/science.1190737

Perspectives

Physics:

The Lamb Shift—Yesterday, Today, and Tomorrow

Marlan O. Scully1 and Anatoly A. Svidzinsky2

1 Texas A&M University, College Station, TX 77843, USA.
2 Princeton University, Princeton, NJ 08544, USA.

E-mail: scully@tamu.edu

The study of the emission and absorption of radiation is the royal road that led Planck to quantum mechanics and Einstein to the concept of the photon. The experiment of Röhlsberger et al. (1) reported on page 1248 of this issue is another step along the way toward explaining changes in the spontaneous light emission from ensembles of emitters. These effects allow us to probe aspects of quantum electrodynamics (QED) in relatively low-energy nuclear experiments.

To put their experiment in perspective, we first need to compare processes with real particles versus those with virtual particles. Although virtual particles have some of the properties of real ones, the former come into existence and then quickly disappear. Spontaneous emission of real photons occurs when an atom or nucleus jumps from an excited state to a lower-energy state. More intriguing are processes in which the atom jumps to an excited state and a virtual photon is emitted, followed quickly by the reverse process in which the atom jumps back to the ground state and now absorbs a photon (see the first figure, panel A). These surreal virtual processes have real effects—they can shift the energy levels of emitting atoms, and are called Lamb shifts after Willis Lamb, who first observed them experimentally (2, 3).

 

Originally published in Science Express on 13 May 2010
Science 4 June 2010:
Vol. 328. no. 5983, pp. 1248 - 1251
DOI: 10.1126/science.1187770

Reports

Collective Lamb Shift in Single-Photon Superradiance

Ralf Röhlsberger,1,* Kai Schlage,1 Balaram Sahoo,1 Sebastien Couet,2 Rudolf Rüffer3

 

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.

 

1 Deutsches Elektronen Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany.
2 Instituut voor Kern- en Stralingsfysica and INPAC, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium.
3 European Synchrotron Radiation Facility, B.P. 220, 38043 Grenoble Cedex, France.

* To whom correspondence should be addressed. E-mail: ralf.roehlsberger@desy.de

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