An atom moving in vacuum at constant velocity parallel to a surface experiences a frictional force induced by the dissipative interaction with quantum electromagnetic fluctuations. We show that the combination of nonequilibrium dynamics, anomalous Doppler effect and spin-momentum locking of light mediates an intriguing interplay between the atom's translational and rotational motion. This behavior deeply affects the drag force in a way that is reminiscent of classical rolling friction. Our fully non-Markovian and nonequilibrium description reveals counterintuitive features characterizing the atom's velocity-dependent rotational dynamics. These results prompt interesting directions for tuning the interaction and for investigating nonequilibrium dynamics as well as the properties of confined light.Quantum light-matter interactions continue to fascinate with intriguing and non-intuitive phenomena. During the last years, many interesting results involving nonequilibrium physics and light confinement in photonic and plasmonic systems have been reported. Although systems out of equilibrium are very common in nature, only recently have intense investigations unraveled their relevance for both fundamental and applied research [1,2]. On the other hand, despite light confinement is already known for inducing many fascinating effects, it still continues to surprise and is currently attracting attention for conveying spin-orbit interactions of light [3][4][5]. Here, we combine these fields of research within a larger framework: We show that, when an atom is forced to move parallel to a surface, a quantum rolling frictional dynamics results from the nonequilibrium interplay of the atomic translational and rotational motion. Despite the underlying physics resembles somewhat that of a body rolling on a surface, it features many interesting counterintuitive aspects.Due to vacuum fluctuations, light-matter interactions lead to the occurrence of non-conservative (frictional) forces on electrically neutral and non-magnetic objects [6,7]. These forces are quantum in nature and the physics behind quantum friction is related to the quantum Cherenkov effect through the anomalous-Doppler effect [8][9][10][11]. In this process, real photons are extracted from vacuum at the cost of the object's kinetic energy; they are absorbed and re-emitted producing a fluctuating momentum recoil [12]. When only the atomic translational motion is considered, spin-zero photons are absorbed and re-emitted, and a net quantum frictional force that opposes the translational motion appears. This anisotropic process was investigated in many scenarios during the last decade [6,[13][14][15][16][17][18][19][20] and its connection to nonequilibrium physics was recently highlighted [21]. In this Letter we show that, when the rotational degrees of freedom are involved in the dynamics, the atom can also exchange angular momentum, absorbing and emitting photons with nonzero spin. However, due to nonequilibrium physics, the anomalous-Doppler effect and the spinmomentum...

The impact of lossy multi-layer structures on nonequilibrium atom-surface interactions is discussed. Specifically, the focus lies on a fully non-Markovian and nonequilibrium description of quantum friction, the fluctuation-induced drag force acting on an atom moving at constant velocity and height above the multi-layer structures. Compared to unstructured bulk material, the drag force for multi-layer systems is considerably enhanced and exhibits different regimes in its velocity and distance dependences. These features are linked to the appearance of coupled interface polaritons within the superlattice structures. Our results are not only useful for an experimental investigation of quantum friction but also highlight a way to tailor the interaction by simply modifying the structural composition of the multi-layer systems.arXiv:1804.01453v1 [cond-mat.mes-hall]

No abstract

The dissipative properties of spatially nonlocal conductors are investigated in the context of quantum friction acting on an atom moving above a macroscopic body. The focus is on an extended version of the hydrodynamic model for the bulk material's electromagnetic response. It is shown that the standard hydrodynamic description is inadequate for evaluating the frictional force since it completely neglects Landau damping. The extended version of the model contains a frequencydependent compressibility factor for the Fermi liquid and qualitatively resolves this issue. For a quantitative assessment, these results are contrasted with those obtained for the more fundamental Boltzmann-Mermin model. Since the latter is technically involved, the simplicity of the extended hydrodynamic model allows for an easier analysis of the impact of nonlocality on quantum friction for other (planar) geometries. This is illustrated with an example involving a thin slab.

No abstract