Enhanced Dispersion Interaction in Confined Geometry

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 (33γ^5/2+13γ^-3/2)/46 at zero temperature, and by (5γ²+γ^-2)/6 at finite temperature, γ=ϵ_in(0)/ϵ_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.