Inhomogeneity-Induced Casimir Transport of Nanoparticles

Abstract

This letter proposes a scheme for transporting nanoparticles immersed in a fluid, relying on quantum vacuum fluctuations. The mechanism lies in the inhomogeneity-induced lateral Casimir force between a nanoparticle and a gradient metasurface, and the relaxation of the conventional Dzyaloshinskiǐ-Lifshitz-Pitaevskiǐ constraint, which allows quantum levitation for a broader class of material configurations. The velocity for a nanosphere levitated above a grating is calculated and can be up to a few microns per minute. The Born approximation gives general expressions for the Casimir energy which reveal size-selective transport. For any given metasurface, a certain particlemetasurface separation exists where the transport velocity peaks, forming a "Casimir passage". The sign and strength of the Casimir interactions can be tuned by the shapes of liquid-air menisci, potentially allowing real-time control of an otherwise passive force, and enabling interesting on-off or directional switching of the transport process.

Thermal spin photonics in the near-field of nonreciprocal media

“…It is well-known that light carrying momentum and spin/orbital angular momentum can exert optical forces and torques on small absorptive particles in its path. Many works have explored this light-matter interaction in optical tweezers [35,48,49] by non-thermal means and in entirely passive systems where forces and torques originate from intrinsic quantum and thermal fluctuations [50][51][52]. We are interested in the latter for non-intrusive (without disturbing thermal equilibrium) detection of the persistent phenomena.…”

Nonequilibrium Casimir effects of nonreciprocal surface waves

“…We note that the lateral Casimir forces for equilibrium systems have been studied previously in Ref. [31][32][33][34][35]. In these systems, lateral force can only arise from nonuniform lateral configurations.…”

Numeric corrections to the proximity-force approximation for lateral Casimir forces

“…k0 = 2π/L. but also in cases of Casimir transport [22] where lateral Casimir forces (F l ≡ η l ×F PFA l ) exerting on a small sphere from a complicated inhomogeneous plate (schematically shown in Fig. 1) are considered and rigorous computations become cumbersome.…”

“…Quantifying η allows simple and fast evaluation of Casimir interactions based on the PFA. This is important not only in cases of < 0.1 where most experiments are involved and exact calculations become impractical [21], but also in cases of Casimir transport [22] where lateral Casimir forces (F l ≡ η l ×F PFA l ) exerting on a small sphere from a complicated inhomogeneous plate (schematically shown in Fig. 1) are considered and rigorous computations become cumbersome.…”

“…4, for increasing r/p. We apply our method to gradient gratings where lateral Casimir forces include displacement-induced and inhomogeneity-induced two components [22],…”