Two corrections to the Lamb shift, induced by the polarization operator insertions in the external photon lines are calculated. PACS numbers: 12.20.Ds, 31.30.Jv Typeset using REVTEX

In contrast to classical empty space, the quantum vacuum fundamentally alters the properties of embedded particles. This paradigm shift allows one to explain the discovery of the celebrated Lamb shift in the spectrum of the hydrogen atom. Here, we engineer a synthetic vacuum, building on the unique properties of ultracold atomic gas mixtures, offering the ability to switch between empty space a...

We present a calculation scheme for the two-loop vacuum polarization correction of order α2 to the Lamb shift of hydrogen-like high-Z atoms. The interaction with the external Coulomb field is taken into account to all orders in (Zα). By means of a modified potential approach the problem is reduced to the evaluation of effective one-loop vacuum polarization potentials. An expression for the ener...

New corrections to the energy of S-levels of positronium of order mα which are as large as several hundred kilohertz are obtained. A new recoil correction of order α(Zα)(m/M)m to the Lamb shift in hydrogen is calculated. This correction turns out to be too small from the phenomenological point of view. 1. Recent progress in the spectroscopy of positronium [1, 2, 3, 4, 5] triggered theoretical w...