Mode structure and polaritonic contributions to the Casimir effect in a magneto-dielectric cavity

We present a full analysis of the mode spectrum in a cavity formed by two parallel plates, one of which is a magneto-dielectric, e.g. a metamaterial, while the other one is metallic, and obtain dispersion relations in closed form. The optical properties of the cavity walls are described in terms of realistic models for the effective permittivity and the permeability. Surface polaritons, i.e. electromagnetic modes that have at least partly an evanescent character, are shown to dominate the Casimir interaction at small separations. We analyze in detail the s-polarized polaritons, which are a characteristic feature of a magneto-dielectric configuration, and discuss their role in the repulsive Casimir force.Comment: 14 pages, 8 figure

Magnetic near fields as a probe of charge transport in spatially dispersive conductors

We calculate magnetic field fluctuations above a conductor with a nonlocal response (spatial dispersion) and consider a large range of distances. The cross-over from ballistic to diffusive charge transport leads to reduced noise spectrum at distances below the electronic mean free path, as compared to a local description. We also find that the mean free path provides a lower limit to the correlation (coherence) length of the near field fluctuations. The short-distance behavior is common to a wide range of materials, covering also semiconductors and superconductors. Our discussion is aimed at atom chip experiments where spin-flip transitions give access to material properties with mesoscopic spatial resolution. The results also hint at fundamental limits to the coherent operation of miniaturized atom traps and matter wave interferometers.Comment: 11 page

Modified and controllable dispersion interaction in a 1D waveguide geometry

Dispersion interactions such as the van der Waals interaction between atoms or molecules derive from quantum fluctuations of the electromagnetic field and can be understood as the exchange of virtual photons between the interacting partners. Any modification of the environment in which those photons propagate will thus invariably lead to an alteration of the van der Waals interaction. Here we show how the two-body dispersion interaction inside a cylindrical waveguide can be made to decay asymptotically exponentially, and how this effect sensitively depends on the material properties and the length scales of the problem, eventually leading to the possibility of controllable interactions. Further, we discuss the possibility to detect the retarded van der Waals interaction by resonant enhancement of the interaction between Rydberg atoms in the light of long-range potentials due to guided modes.Comment: 9 pages, 6 figure

Thermal effects in the magnetic Casimir-Polder interaction

We investigate the magnetic dipole coupling between a metallic surface and an atom in a thermal state, ground state and excited hyperine state. This interaction results in a repulsive correction and - unlike the electrical dipole contribution - depends sensitively on the Ohmic dissipation in the material

Polaritonic states in a dielectric nanoguide: localization and strong coupling

Propagation of light through dielectrics lies at the heart of optics. However, this ubiquitous process is commonly described using phenomenological dielectric function $\varepsilon$ and magnetic permeability $\mu$, i.e. without addressing the quantum graininess of the dielectric matter. Here, we present a theoretical study where we consider a one-dimensional ensemble of atoms in a subwavelength waveguide (nanoguide) as fundamental building blocks of a model dielectric. By exploring the roles of the atom-waveguide coupling efficiency, density, disorder, and dephasing, we establish connections among various features of polaritonic light-matter states such as localization, super and subradiance, and strong coupling. In particular, we show that coherent multiple scattering of light among atoms that are coupled via a single propagating mode can gives rise to Rabi splitting. These results provide important insight into the underlying physics of strong coupling reported by recent room-temperature experiments with microcavities and surface plasmons.Comment: 10 pages, 6 figure

Chiral emission into nanophotonic resonators

Chiral emission, where the handedness of a transition dipole determines the direction in which a photon is emitted, has recently been observed from atoms and quantum dots coupled to nanophotonic waveguides. Here, we consider the case of chiral light-matter interactions in resonant nanophotonic structures, deriving closed-form expressions for the fundamental quantum electrodynamic quantities that describe these interactions. We show how parameters such as the position dependent, directional Purcell factors and mode volume can be calculated using computationally efficient two dimensional eigenmode simulations. As an example, we calculate these quantities for a prototypical ring resonator with a geometric footprint of only 4.5~$\mu$m$^2$, showing that perfect directionality with a simultaneous Purcell enhancement upwards of 400 are possible. The ability to determine these fundamental properties of nanophotonic chiral interfaces is crucial if they are to form elements of quantum circuits and networks

Feynman Diagrams for Dispersion Interactions Out of Equilibrium -- Two-Body Potentials for Atoms with Initial Excitation

Diagrammatic techniques are well-known in the calculation of dispersion interactions between atoms or molecules. The multipolar coupling scheme combined with Feynman ordered diagrams significantly reduces the number of graphs compared to elementary stationary perturbation theory. We review calculations of van der Waals-Casimir-Polder forces, focusing on two atoms or molecules one of which is excited. In this case, calculations of the corresponding force are notorious for mathematical issues connected to the spontaneous decay of the excitation. Treating such unstable states in a full non-equilibrium theory provides a physical interpretation of apparent contradictions in previous results and underlines the importance of decay processes for the intermolecular potential. This may have important implications on reactions in biological systems, where excited states may be relatively long-lived and the resonant intermolecular force may result in directed Brownian motion.Comment: Proceedings of Quantum Field Theory under External Conditions (QFExt) 201

Large suppression of quantum fluctuations of light from a single emitter by an optical nanostructure

We investigate the reduction of the electromagnetic field fluctuations in resonance fluorescence from a single emitter coupled to an optical nanostructure. We find that such hybrid system can lead to the creation of squeezed states of light, with quantum fluctuations significantly below the shot noise level. Moreover, the physical conditions for achieving squeezing are strongly relaxed with respect to an emitter in free space. A high degree of control over squeezed light is feasible both in the far and near fields, opening the pathway to its manipulation and applications on the nanoscale with state-of-the-art setups.Comment: 10 pages, 5 figure