An object that is immersed in a fluid and approaching a substrate may find a potential energy minimum at a certain distance due to the balance between attractive and repulsive Casimir−Lifshitz forces, a phenomenon referred to as quantum trapping. This equilibrium strongly depends on the relative values of the dielectric functions of the materials involved. Herein, we study quantum trapping effects in two exemplary planar photonic structures.
On the one hand, we investigate the building of an optical resonator based on the levitation properties of a thin bilayer film subjected to strong repulsive Casimir−Lifshitz forces at finite temperature when immersed in an adequate medium and confronted with a planar substrate . We propose a design in which cavities supporting high Q-factor optical modes at visible frequencies can be achieved by means of combining commonly found materials, such as silicon oxide, polystyrene, or gold, with glycerol as a mediating medium. The spectroscopic characterization of the optical resonator determines the size of the cavity and, indirectly, the equilibrium distance at which the bilayer structure levitates.
On the other hand, we study quantum trapping effects at finite temperature in planar nanocomposite materials and demonstrate that they are strongly dependent on the characteristics of the spatial inhomogeneity . As a model case, we consider polystyrene spherical particles embedded in an otherwise homogeneous silicon oxide material. We propose an effective medium approximation that accounts for the effect of inclusions and find that an unprecedented and counterintuitive intense repulsive Casimir−Lifshitz force arises as a result of the strong optical scattering and absorption size-dependent resonances caused by their presence.
Our results constitute a proof of concept that may open the route to the design of photonic architectures in environments in which dispersion forces play a substantial role.
 V. Esteso, S. Carretero Palacios, H. Míguez, J. Phys. Chem. Lett. 2019, 10, 5856−5860
 V. Esteso, S. Carretero Palacios, H. Míguez, J. Phys. Chem. Lett. 2022, 13, 4513−4519