LambVerschiebung

Lamb Verschiebung, known in English as the Lamb shift, is the small energy difference between the 2S1/2 and 2P1/2 electron states in the hydrogen atom (and in hydrogen-like systems). In Dirac theory these states are degenerate, but quantum electrodynamics corrections lift this degeneracy, producing the Lamb shift. The observed transition frequency is about 1057.8 MHz, corresponding to an energy difference of roughly 4.4 microelectronvolts.

Discovered experimentally in 1947 by Willis Lamb and his colleague Retherford using microwave spectroscopy of atomic hydrogen, the result provided a critical test for quantum electrodynamics and prompted theories incorporating radiative corrections such as electron self-energy and vacuum polarization. Bethe's initial nonrelativistic calculation explained the magnitude, while later fully relativistic QED treatments by Schwinger, Feynman, and others yielded precise agreement with measurements.

Mechanism: The shift arises from the interaction of the bound electron with vacuum fluctuations and its own electromagnetic field, leading to self-energy corrections and vacuum polarization that depend on the electric field seen by the electron in specific orbital states. The effect scales roughly as Z^4 in hydrogen-like ions, making measurements across systems a sensitive probe of QED across regimes.

Significance: The Lamb shift was a pivotal empirical validation of quantum electrodynamics and influenced the refinement of fundamental constants and precision spectroscopy. It remains a benchmark observable in atomic structure and tests of quantum field theory.

German usage: In German-language literature, the term is Lamb-Verschiebung or Lambverschiebung.