Lambskift

Lambskift, or Lamb shift, is the small energy difference between the 2S1/2 and 2P1/2 energy levels of the hydrogen atom. In the Dirac equation, these two states would be degenerate, but in reality they are split due to quantum electrodynamics effects that modify the electron’s interaction with the electromagnetic field.

The shift arises from radiative corrections, including vacuum fluctuations of the electromagnetic field and the electron’s self-energy. These effects alter the energy of the electron differently in the 2S and 2P states, producing a measurable difference. The Lamb shift corresponds to a frequency of about 1,057 MHz, or roughly a few microelectronvolts in energy.

History and theory: The shift was predicted and demonstrated experimentally in 1947 by Willis Lamb and Robert Retherford through precision microwave spectroscopy of atomic hydrogen. The result provided a pivotal test of quantum electrodynamics (QED). A quantitative explanation followed from Bethe’s calculation and was refined by subsequent QED work, which confirmed that radiative corrections account for the observed splitting.

Significance: The Lamb shift is regarded as one of the first precise empirical validations of QED and a cornerstone in modern atomic physics. It helped drive the development of high-precision spectroscopy and led to more accurate determinations of fundamental constants. While originally observed in hydrogen, the underlying radiative shift concept extends to other atomic systems and remains a standard benchmark for QED calculations. See also quantum electrodynamics; hydrogen spectrum; fine structure.