Lamb shift discovery

Many experiments on the precise measurement of the classic Lamb shift were performed since its experimental discovery in 1947. We have collected modern post 1979 experimental results in Table 12.2. Two entries in this Table are changed compared to the original published experimental results [16, 15]. These alterations reflect recent improvements of the theory used for extraction of the Lamb shift value from the raw experimental data. 

The discovery of the 25 — 2P Lamb shift has led to the development of the theory of quantum electrodynamics. Today, radio frequency measurements of this splitting have reached the uncertainty limits imposed by the 100 MHz natural linewidth of the 2P state. The considerably sharper optical two-photon resonances used in optical experiments leave significant room for future improvements. 

Breit was the first to suggest [3] that the unanticipated results of hyperfine measurements [4,5] may be explained if the electron g value deviates slightly from 2, the Dirac value. This observation was soon confirmed by the experiment of Kusch and Foley [6]. Together with the discovery of the Lamb shift in the spectrum of hydrogen atom, this provided a timely stimulus for the renormalization... 

Hydrogen-like atoms have served extensively as very successful probes of the basic aspects of the laws of physics. It is the detailed investigation of the hydrogen atom that led to the development of quantum mechanics and it is the discovery of the Lamb shift in 1947 [1] that motivated the description of physical processes via quantum field theory. Clearly, it is by further precision measurements that unexpected features of physical law can be discovered. 

The 1S-2S transition in muonium has also been measured by laser spectroscopy. The transition is induced by a two-photon Doppler-free process and detected through the subsequent photoionization of the 2S state in the laser field. The key to success in this experiment was the production of muonium into vacuum from the surface of heated W or of Si02 powder. The discovery experiment(33) was done at the KEK facility in Japan with a pulsed muon beam and an intense pulsed laser system. A subsequent experiment(34) done with the pulsed beam at RAL and a similar pulsed laser has improved the signal substantially and has achieved a a precision of about lO" in the 1S- 2S interval, thus determining the Lamb shift in the IS state to about 1% accuracy (Fig. 22). The precision of this experiment should be greatly improved in a new experiment now underway at RAL. This experiment will provide a precise... 

In the historical development of science, experimental progress in the accuracy of measurements have often brought about a refinement of theoretical models or even the introduction of new concepts [14.1]. Examples are A. Einstein s theory of special relativity based on the interferometric experiments of Michel son and Morley [14.2] M. Planck s introduction of quantum physics for the correct explanation of the measured spectral distribution of black-body radiation, the introduction of the concept of electron spin after the spectroscopic discovery of the fine structure in atomic spectra [14.3] or the test of quantum-electrodynamics by precision measurements of the Lamb shift [14.4]. 

With the envisioned higher resolution, it should be possible to determine a better value of the electron/proton mass ratio from a precise measurement of the isotope shift. And a measurement of the absolute frequency or wavelength should provide a new value of the Rydberg constant with an accuracy up to 1 part in 10, as limited by uncertainties in the fine structure constant and the mean square radius of the proton charge distribution. A comparison with one of the Balmer transitions, or with a transition to or between Rydberg states could provide a value for the IS Lamb shift that exceeds the accuracy of the best radiofrequency measurements of the n=2 Lamb shift. Such experiments can clearly provide very stringent tests of quantum electrodynamic calculations, and when pushed to their limits, they may well lead to some surprising fundamental discovery. 

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