CasimirPolder

Casimir-Polder, or the Casimir–Polder effect, is a quantum electrodynamical force arising from vacuum fluctuations of the electromagnetic field, producing a long-range interaction between neutral particles or between a neutral particle and a surface. It was predicted in 1948 by Hendrik B. Casimir and Dirk Polder, extending the London dispersion forces to include retardation effects due to the finite speed of light. The effect can be derived from quantum electrodynamics by considering the interaction of an atom’s polarizability with the quantized electromagnetic field modes under boundary conditions.

For two neutral atoms, at short separations the interaction follows the van der Waals force with a representative r^-6 dependence; at larger separations retardation becomes important and the potential scales as r^-7. For an atom near a macroscopic body such as a conducting plate, the force depends on the distance z from the surface and the material properties; in the nonretarded regime it scales roughly as z^-3, while in the retarded regime it falls off as z^-4. The magnitude is governed by the atom’s dynamic polarizability α(ω) and the electromagnetic response of the surface.

Experimental observations include measurements with atomic beams, precision spectroscopy near surfaces, and ultracold atoms or Bose–Einstein condensates in proximity to surfaces. The Casimir-Polder effect is central to studies of quantum vacuum forces, atom–surface interactions, and nanoscale physics, with implications for precision measurements and the design of micro- and nanoelectromechanical systems.