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During the past few decades, abundant evidence for physics beyond the two standard models of particle physics and cosmology was found. Yet, we are tapping into the dark regarding our understanding of the dark sector. For more than a century, open problems related to the nature of the vacuum remain unresolved. Besides the traditional high-energy frontier and cosmology, technological advancement provides complementary access to new physics via high-precision experiments. Among the latter, the Casimir And Non-Newtonian force EXperiment (\cannex{}) has successfully completed its proof-of-principle phase and will soon commence operation. Benefiting from its plane parallel plate geometry, both interfacial and gravity-like forces are maximized, leading to increased sensitivity. A wide range of dark sector forces, Casimir forces in and out of thermal equilibrium, and gravity will be tested. This article describes the final experimental design, its sensitivity, and expected results.

For systems in equilibrium, quantum statistical physics provides a number of general theorems and relations that are not tied to specific microscopic models, one example being the fluctuation-dissipation theorem. Much less is known for nonequilibrium situations. In this work, we discuss certain properties of the power-spectrum tensor for systems in general steady-states, i.e. stationary states not necessarily corresponding to equilibrium configurations. In our analyses, we do not make any direct connection to specific models for the underlying microscopic dynamics and, therefore, our results can be applied to a large variety of systems. We also connect the power-spectrum tensor to other quantities that characterize these systems and, where appropriate, compare with the equilibrium counterparts. As an application, we consider the specific problem of quantum friction, where, at zero temperature, a contactless quantum-electrodynamic drag force acts on a particle that moves in close proximity to an arrangement of material bodies. Specifically, we show how the additional information about the system's physics facilitates the derivation of more precise constraints on the power spectrum and its functional dependencies., Comment: 13 pages, 1 figure

We describe a numerical time-domain approach for high-accuracy calculations of Casimir-Polder forces near micro-structured materials. The use of a time-domain formulation enables the investigation of a broad range of materials described by advanced material models, including nonlocal response functions. We validate the method by a number of example calculations for which we thoroughly investigate the convergence properties of the method, and comparing to analytical reference calculations, we find average relative errors as low as a few parts in a million. As an application example, we investigate the anisotropy-induced repulsive behavior of the Casimir-Polder force near a sharp gold wedge described by a hydrodynamic Drude model., Comment: 17 pages, 11 figures

Modes have steadily influenced the understanding of physical systems through time. At least since the prediction of the Casimir effect, they also play a very important role in Casimir Physics and in the understanding of the different phenomena typical of this research field. At equilibrium modes provide a direct connection between the zero-point energy and the existence of irreducible fluctuations in a quantum system, offering an anatomic view into the physics of the interaction. In nonequilibrium systems, modes can be decisive to understand the behavior of quantum fluctuation-induced phenomena, highlighting key aspects which determine their strength and their functional dependence. In this article we review some recent studies and results that highlight how modes impact Casimir physics and the central role they play in shaping our understanding of this area of research., Comment: 30 pages, 10 figures

The nonlocal response of plasmonic materials and nanostructures is usually described within a hydrodynamic approach which is based on the Euler-Drude equation. In this work, we reconsider this approach within linear response theory and employ Halevi's extension to this standard hydrodynamic model. After discussing the impact of this improved model, which we term the Halevi model, on the propagation of longitudinal volume modes, we accordingly extend the Mie-Ruppin theory. Specifically, we derive the dispersion relation of cylindrical surface plasmons. This reveals a nonlocal, collisional damping term which is related to earlier phenomenological considerations of limited-mean-free-path effects and influences both, peak width and amplitude of corresponding resonances in the extinction spectrum. In addition, we transfer the Halevi model into the time-domain thereby revealing a novel, diffusive contribution to the current which shares certain similarities with Cattaneo-type currents and analyze the resulting hybrid, diffusive-wave-like motion. Further, we discuss the relation of the Halevi model to other approaches commonly used in the literature. Finally, we demonstrate how to implement the Halevi model into the Discontinuous-Galerkin Time-Domain finite-element Maxwell solver and are able to identify an oscillatory contribution to the diffusive current. The Halevi model thus captures a number of relevant features beyond the standard hydrodynamic model. Contrary to other extensions of the standard hydrodynamic model, its use in time-domain Maxwell solvers is straightforward -- especially due its affinity to a class of descriptions that allow for a clear distinction between bulk and surface response. This is of particular importance for applications in nano-plasmonics where nano-gap structures and other nano-scale features have to be modeled efficiently and accurately., Comment: 20 pages, 7 figures, 1 tables

Efficient modeling of dispersive materials via time-domain simulations of the Maxwell equations relies on the technique of auxiliary differential equations. In this approach, a material's frequency-dependent permittivity is represented via a sum of rational functions, e.g. Lorentz-poles, and the associated free parameters are determined by fitting to experimental data. In the present work, we present a modified approach for plasmonic materials that requires considerably fewer fit parameters than traditional approaches. Specifically, we consider the underlying microscopic theory and, in the frequency domain, separate the hydrodynamic contributions of the quasi-free electrons in partially filled bands from the interband transitions. As an illustration, we apply our approach to gold and demonstrate how to treat the interband transitions within the effective model via connecting to the underlying electronic bandstructure, thereby assigning physical meaning to the remaining fit parameters. Finally, we show how to utilize this approach within the technique of auxiliary differential equations. Our approach can be extended to other plasmonic materials and leads to efficient time-domain simulations of plasmonic structures for frequency ranges where interband transitions have to be considered., Comment: 9 pages, 3 figures, 1 table

Fluctuations are ubiquitous in nature. They are one of the fundamental building blocks of quantum mechanics and are responsible for a wide variety of phenomena in many areas of physics, ranging from biology to cosmology. Far from any classical intuition, quantum fluctuations are for instance responsible for the appearance of forces between non-magnetic and electrically neutral objects in vacuum, which seem to arise out of nothing. Ever since, quantum fluctuations have fascinated basic research providing new insights into physics and their understanding is becoming increasingly important for various future technologies. -- Fluktuationen sind allgegenw\"{a}rtig. Sie bilden einen fundamentalen Baustein der Quantenmechanik und sind verantwortlich f\"{u}r die unterschiedlichsten Ph\"{a}nomene, angefangen in der Biologie bis hin zur Kosmologie. Fern jeder klassischen Intuition findet man zum Beispiel Kr\"{a}fte zwischen nichtmagnetischen und elektrisch neutralen Objekten. Einzig bedingt durch Quantenfluktuationen entstehen diese Kr\"{a}fte wie aus dem Nichts. Seit jeher begeistern sie die Grundlagenforschung mit neuen Einsichten und gewinnen immer mehr an Bedeutung f\"{u}r verschiedene Zukunftstechnologien., Comment: 8 pages, 4 figures, 4 pictures. Overview paper in German. Appeared in a modified form in the May issue of the Physik Journal (journal of the German Physical Society - DPG)

When two or more objects move relative to one another in vacuum, they experience a drag force which, at zero temperature, usually goes under the name of quantum friction. This contactless non-conservative interaction is mediated by the fluctuations of the material-modified quantum electrodynamic vacuum and, hence, is purely quantum in nature. Numerous investigations have revealed the richness of the mechanisms at work, thereby stimulating novel theoretical and experimental approaches and identifying challenges as well as opportunities. In this article, we provide an overview of the physics surrounding quantum friction and a perspective on recent developments., Comment: 15 pages, 2 figures

We investigate the nonconservative open-system dynamics of an atom in a generic complex structured electromagnetic environment at temperature $T$. In such systems, when the atom moves along a translation-invariant axis of the environment, a frictional force acts on the particle. The effective viscosity due to friction results from the nonequilibrium interaction with the fluctuating (quantum) electromagnetic field, which effectively sets a privileged reference frame. We study the impact of both quantum or thermal fluctuations on the interaction and highlight how they induce qualitatively different types of viscosity, i.e. quantum and black-body friction. To this end, we develop a self-consistent non-Markovian description that contains the latter as special cases. In particular, we show how the interplay between the nonequilibrium dynamics, the quantum and the thermal properties of the radiation, as well as the confinement of light at the vacuum-material interface is responsible for several interesting and intriguing features. Our analyses is relevant for a future experimental test of noncontact friction and the resulting electromagnetic viscosity., Comment: 16 pages, 8 figures

We show that the performance and functionality of atom-chips can be transformed by using graphene-based van der Waals heterostructures to overcome present limitations on the lifetime of the trapped atom cloud and on its proximity to the chip surface. Our analysis involves Green-function calculations of the thermal (Johnson) noise and Casimir-Polder atom-surface attraction produced by the atom-chip. This enables us to determine the lifetime limitations produced by spin-flip, tunneling and three-body collisional losses. Compared with atom-chips that use thick metallic conductors and substrates, atom-chip structures based on two-dimensional materials reduce the minimum attainable atom-surface separation to a few 100 nm and increase the lifetimes of the trapped atom clouds by orders of magnitude so that they are limited only by the quality of the background vacuum. We predict that atom-chips with two-dimensional conductors will also reduce spatial fluctuations in the trapping potential originating from imperfections in the conductor patterns. These advantages will enhance the performance of atom-chips for quantum sensing applications and for fundamental studies of complex quantum systems., Comment: 22 pages, 14 figures

Thermodynamic principles are often deceptively simple and yet surprisingly powerful. We show how a simple rule, such as the net flow of energy in and out of a moving atom under nonequilibrium steady state condition, can expose the shortcomings of many popular theories of quantum friction. Our thermodynamic approach provides a conceptual framework in guiding atom-optical experiments, thereby highlighting the importance of fluctuation-dissipation relations and long-time correlations between subsystems. Our results introduce consistency conditions for (numerical) models of nonequilibrium dynamics of open quantum systems., Comment: 10 pages, 1 figure

We study the role of surface polaritons in the zero-temperature Casimir effect between two graphene layers that are described by the Dirac model. A parametric approach allows us to accurately calculate the dispersion relations of the relevant modes and to evaluate their contribution to the total Casimir energy. The resulting force features a change of sign from attractive to repulsive as the distance between the layers increases. Contrary to similar calculations that have been performed for metallic plates, our asymptotic analysis demonstrates that at small separations the polaritonic contribution becomes negligible relative to the total energy.

The motion-induced drag force acting on a particle moving parallel to an arrangement of $N$ objects is analyzed. Particular focus is placed on the nonequilibrium statistics of the interaction and on the interplay between the system's geometry and the different dissipative processes occurring in realistic setups. We show that the drag force can exhibit a markedly nonadditive enhancement with respect to the corresponding additive approximation. The specific case of a planar cavity -- a relevant configuration for many experiments -- is calculated, showing an enhancement of about one order of magnitude. This and similar configurations are of significant potential interest for future measurements that aim to detect the drag force., Comment: 9 pages, 3 figures

We present a bi-orthogonal approach for modeling the response of localized electromagnetic resonators using quasinormal modes, which represent the natural, dissipative eigenmodes of the system with complex frequencies. For many problems of interest in optics and nanophotonics, the quasinormal modes constitute a powerful modeling tool, and the bi-orthogonal approach provides a coherent, precise, and accessible derivation of the associated theory, enabling an illustrative connection between different modeling approaches that exist in the literature.

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 frequency-dependent 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., Comment: 12 pages, 5 figures