Resonant van der Waals Repulsion between Excited Cs Atoms and Sapphire Surface

Abstract

We explore a situation where the van der Waals long-range atom-surface interaction is repulsive. This repulsion originates in a resonant coupling between a virtual emission at 12.15 mm of a Cs ‫ء‬ ͑6D 3͞2 ͒ atom and a virtual excitation of a surface polariton in sapphire. The experimental evidence is based upon the analysis of the spectroscopic response of Cs* in the near-infrared range with a technique that probes a distance range ϳ100 nm away from the sapphire surface. We also demonstrate the critical dependence of atom-surface forces on the sapphire crystal orientation. PACS numbers: 34.50.Dy, 12.20.Fv, 71.36. + c The van der Waals (vW) force between neutral polarizable systems [1,2] represents a universal interaction of paramount importance in numerous fields of physics, chemistry, and biology. Its attractive character is essential for the cohesion of many chemical or biological systems. vW attraction between atomic systems and metallic or dielectric bodies is also a fundamental property in cavity quantum electrodynamics (QED) [3], and its main characteristics have been experimentally studied by means of mechanical approaches (atomic beam deflection produced by surfaces [4,5], energy threshold in atomic mirrors [6]), or, in our group, spectroscopic approaches (spectral monitoring of surface-induced atomic level shifts [7-10]).In the nonretarded regime, the vW interaction between an atom and a surface originates in the quantum fluctuations of the atomic dipole: The fluctuating dipole polarizes the surface, and induces a dipole image instantaneously correlated with the atomic dipole. This near-field image is responsible for the attractive character of the vW interaction, which scales in 1͞z 3 (z is the atom-surface distance) [1].Is it possible to turn this near-field attraction into a repulsion? The answer is yes, if a resonant coupling between the fluctuating atomic dipole and a surface excitation can occur [11][12][13]. For a dispersive dielectric medium with a complex permittivity´͑v͒, the well-known electrostatic image coefficient S ͑´2 1͒͑͞´1 1͒ (with 0 # S # 1) has to be generalized to a complex frequency-dependent surface response [13]:whose resonances ("surface polaritons" [14]) are determined by the poles of S͑v͒.Consider an excited atom for which one of the dipoleallowed deexcitation channels (at frequency v a ) is near resonant with a surface polariton. Because of nonradiative, virtual coupling between the atom and surface (atomic decay followed by surface excitation), the surface response at frequency v a is magnified, implying a dielectric image coefficient, 2Re͓S͑v a ͔͒, possibly larger than one-the value obtained for an ideal reflector. Because of the resonant enhancement, S is complex and the image dipole is dephased as well. When this image is phase reversed, the near-field vW attraction is turned into a near-field vW repulsion, also scaling in 1͞z 3 . This is one among the rare situations of a long-range, state-selective repulsion exerted by a cavity wall on an atom, at distances spanning f...

van der Waals interaction of excited media

“…At some points it is about three orders of magnitude. But our result (44) coincides with the well known theoretical results 9 10 11 12 and experimental ones 10,13,14 . Thus, failure of the polarizabilities of atoms (37) and (38) but they contain the so-called coherent polarizabilities The analysis of the interaction between two atoms enabled us to calculate the van der Waals potential for the interaction of a single atom with a semi-infinite medium.…”

“…The propagator B g obeys equation (13). For the sake of simplicity, in equation (13) we take into account only interaction of atom B with the vacuum, which is described by the mass operator given in Fig.2a, where the solid line represents 0 B g .…”

“…The same separation of channels appears in Γ-operator technique 20 . Now we take into account the higher orders of perturbation technique and use the well known Dyson equation for photon and electron propagators (13) and (16). It is easy to show that we should substitute complete electron and photon propagators satisfying the Dyson equations (13) and (16) into the equation ( 58) instead of free field propagators and add a term appearing in the fourth order of perturbation technique and shown in fig.9.…”

Temperature dependence of the magnetic Casimir-Polder interaction

“…Before addressing these, we start with thermal equilibrium free energies, however. This may be not an unrealistic assumption in spectroscopic experiments where Casimir-Polder energies are measured with atoms near the window of a vapor cell [56]. From the theoretical viewpoint, thermal equilibrium provides an unambiguous definition of the entropy related to the atom-surface interaction.…”

Selective reflection technique as a probe to monitor the growth of metallic thin film on dielectric surfaces

“…The technique was used, for instance, (i) to measure the van der Waals (vW) atom-surface interaction for atomic short-lived excited states [14,15]; (ii) to measure resonant effects between atomic transitions and surface polariton modes that might change the vW interaction into repulsive [16] or induce a surface temperature dependence of the vW force [17]; (iii) to probe linewidth modifications due to atom-atom collisions [18,19]. Furthermore, the SR lineshape is modified if an intermediary layer is introduced between the substrate and the vapor [20,21] and this reflection technique has therefore been suggested as an adequate tool to probe films thickness in such structures.…”