The dispersion interaction between two pointlike particles confined in a dielectric slab between two plates of another dielectric medium is studied within a continuum (Lifshitz) theory. The retarded (Casimir-Polder) interaction at large interparticle distances is found to be strongly enhanced as the mismatch between the dielectric permittivities of the two media is increased. The large-distance interaction is multiplied due to confinement by a factor of $(33{\gamma }^{5/2}+13{\gamma }^{-3/2})/46$ at zero temperature, and by $(5{\gamma }^2+{\gamma }^{-2})/6$ at finite temperature, $\gamma ={ϵ}_{\mathrm{in}}(0)/{ϵ}_{\mathrm{out}}(0)$ being the ratio between the static dielectric permittivities of the inner and outer media. This confinement-induced amplification of the dispersion interaction can reach several orders of magnitude.

• Received 17 August 2005

DOI:https://doi.org/10.1103/PhysRevLett.95.223203