Atom field interactions and entanglement

Quantum optics methods have been employed to discover novel, powerful mechanisms for:

  1. atom-atom and
  2. photon-photon interactions and entangelment.
  3. Translational-internal entanglement in a single particle has been studied.

Long-range bath-induced dispersive interactions
The key to bath induced entanglement (BIE) is virtual quanta exchange via the bath (see topic "Quantumness control in Open Systems")
In free space the mode functions of the photonic bath are 3d plane waves, giving rise to real and virtual quanta exchange which both decay with interatomic separations r and correspond to Dicke-like cooperative emission/absorption and to cooperative Lamb shifts (i.e. resonant dipole–dipole interaction—RDDI), respectively. Whereas for interatomic separations r longer than the resonant atomic wavelength the real- and virtual-photon processes are comparable (scaling as 1/r), in the near-field zone, i.e. for small r, the RDDI retains the familiar dipole-dipole scaling as 1/r3 and can greatly exceed cooperative decay. Therefore, only in the near-field zone can free-space RDDI lead to predominantly deterministic BIE. In contrast, RDDI-induced entanglement is never deterministic at separations beyond the emission wavelength, where incoherent absorption and emission render it probabilistic.