Modern Physics Letters A

Contaminants on the boundary surfaces lead to electric potential inhomogeneities. The resulting poorly defined electric force leads to ambiguities in precision Casimir force measurements. We experimentally demonstrate that with UV light followed by Ar ion beam radiation the electrostatic effects from these patch potentials can be eliminated. The cleaning procedure discussed reduces the sphere-plate potential difference to near zero. In addition, the UV radiation results in vacuum chamber pressures being reduced by a factor of 10 from the removal of volatile molecular species. This leads to very stable and near zero sphere-plate potential differences. The reported combination UV and Ar ion in situ cleaning procedure will find wide application.

Many precision experiments have been done in the Casimir regime and in short range gravity when the separation between the interacting bodies is in the sub-micron range. Experimental complexity is minimized when one of the bodies is a sphere and the other one is a plate, making the alignment between the two bodies ubiquitous. Our group has produced the most precise Casimir measurements, and the best limits on predicted Yukawa-like potentials by measuring a force between a $R\sim 150\mu \mathrm{\text{m}}$ sphere attached to a ${(500\mu \mathrm{\text{m}})}^2$ micro-mechanical oscillator and a planar source mass. By replacing the spherical surface with a fraction of a $500\mu \mathrm{\text{m}}$ long cylinder with $R\sim 150\mu$m, the force sensitivity can be greatly enhanced. Here, it is paramount to know the angular deviation between the long axis of the cylinder and both the axis of rotation of the oscillator and the plate. Tests between a cylinder and a structure etched into a silicon wafer show that deviations of $20\mu$rad are readily accessible. Additionally, a scaled up experiment is used to investigate if capacitance measurements can determine the orientation of the cylinder with respect to a plane with the required precision.

The dependence of the Casimir force on the optical properties and geometry of interacting materials makes possible to tailor the actuation dynamics of micro/nano actuators. In this research, we study the dynamical sensitivity of micro- and nanoelectromechanical systems on geometry by comparing the plate-plate and sphere-plate configurations, and taking into account the optical properties of the interacting materials. In fact, for conservative systems bifurcation analysis and phase portraits show that the geometry and the optical properties strongly influence the stability of an actuating device in a way that geometries that lead to weaker Casimir forces (sphere-plate geometry) favor more stable behavior. In addition, for non-conservative periodically driven systems, the Melnikov and Poincare portrait analysis shows that stronger Casimir forces lead to increased chaotic behavior, which more pronounced for the plate-plate geometry, that prohibits the long term prediction of the actuating dynamics of the system.

We find the low-temperature behavior of the Casimir-Polder free energy and entropy for an atom interacting with real graphene sheet possessing nonzero energy gap and chemical potential. Employing the formalism of the polarization tensor, it is shown that the Casimir-Polder entropy goes to zero by the power law with vanishing temperature, i.e., the Nernst heat theorem is satisfied. This result is discussed in connection with the problems connected with account of free charge carriers in the Lifshitz theory.

We investigate Bose-Einstein condensation of a gas of non-interacting Bose particles moving in the background of a periodic lattice of delta functions. In the one-dimensional case, where one has no condensation in the free case, we showed that this property persist also in the presence of the lattice. In addition we formulated some conditions on the spectral functions which would allow for condensation.

A new solution for an analytic spectrum of particle creation by an accelerating mirror (dynamical Casimir effect) is given. It is the first model to simultaneously radiate thermally and emit a finite number of particles.

We consider experiments on measuring the Casimir interaction which have been performed in the last four years. The emphasis is made on measuring differences in the Casimir pressures under a transition of the plate metal from normal to superconducting state and on the Casimir metrology platform using a commercial micromechanical sensor. In both cases several problems in the comparison between experiment and theory are discussed.

The Casimir energy for a massless, neutral scalar field in presence of a point interaction is analyzed using a general zeta-regularization approach developed in earlier works. In addition to a regular bulk contribution, there arises an anomalous boundary term which is infinite despite renormalization. The intrinsic nature of this anomaly is briefly discussed.

We provide a brief review of the contribution of thermally excited carriers to dispersion forces. In a metal, these carriers generate charge and current fluctuations whose spectral frequencies are comparable to $k_{B}T/\hslash$. They are very likely responsible for the “plasma vs. Drude” anomaly.

We find the low-temperature behavior of the Casimir-Polder free energy for a polarizable and magnetizable atom interacting with a plate made of ferromagnetic dielectric material. It is shown that the corresponding Casimir-Polder entropy goes to zero with vanishing temperature, i.e., the Nernst heat theorem is satisfied, if the dc conductivity of the plate material is disregarded in calculations. If the dc conductivity is taken into account, the Nernst theorem is violated. These results are discussed in light of recent experiments.

The effect of resonances in the photon emission rate in radiative heat generation and transfer, and Casimir friction at the relative sliding of two plates of polar dielectrics is studied. Resonances are of a different origin in the frequency range of the normal (NED) and anomalous (AED) Doppler effect. In the NED domain, resonances are associated with resonant photon tunneling between surface phonon/plasmon polaritons. In the AED domain resonances are associated with the instantaneous generation of excitations in both plates. While in the NED domain the resonances are finite, in the ADE domain singular resonances are possible even in the presence of dissipation in the system.

The Casimir energy is constructed for a system consisting of two semi-infinite slabs of anisotropic material. Each of them is characterized by bulk complex dielectric permittivity tensor and surface conductivity on the free boundary. We found general form of the scattering matrix and Fresnel coefficients for each part of the system by solving Maxwell equations in the anisotropic media.

Our recent theoretical developments related to the nonrelativistic and relativistic fluctuation-electromagnetic interactions of bodies with different temperatures moving translationally and (or) rotationally relative to each other are briefly summarized. Three basic geometrical configurations and physical systems are discussed: “a small particle and a thick plate” (i); “a small particle in a radiative vacuum background” (ii) and “two thick plates in relative motion” (iii) — classical Casimir-Lifshitz configuration with allowance for relative motion and different temperatures of plates. For configuration 3, it is shown that the theory of friction and heat exchange by Levin-Polevoi-Rytov proves to be quite adequate contrary to the settled point of view of many authors.

Dispersion forces start to play an important role when the bodies are separated by the distances smaller than 100 nm. Such small gaps characterize modern nano- or microelectromechanical systems. Although the forces were reliably measured and compared to the theory in the range of 30–100 nm, severe problems appear at distances shorter than 30nm due to jump-to-contact instability. In this paper we propose a new measurement method, which does not suffer the short-distance instability. The method is based on the shape of an adhered cantilever that is sensitive to the forces acting near the adhered end. Two values are measured simultaneously: the dispersion pressure at minimal separation (close to contact) and the adhesion energy. Roughness of interacting surfaces plays a crucial role. We discuss possible realization of this experiment and propose the choice of optimal parameters.

Casimir interaction of two SiO₂ glass half spaces being substrates for Chern-Simons boundary layers is studied. The separation between two half spaces at which the Casimir energy minimum occurs is strongly increased for dielectric SiO₂ glass substrates in comparison with previously considered metal Au and semiconductor Si substrates. Strong reduction in the Casimir force due to presence of Chern-Simons layers is found for SiO₂ glass substrate. Influence of modification of the infrared absorption on the Casimir force is studied.

We investigate the Casimir pressure between two dissimilar plates separated by a layer of magnetic fluid. Numerical computations of the Casimir pressure are performed for Au and SiO₂ plates with an intervening layer of water and water-based ferrofluid obtained on addition to water a 5% volume fraction of magnetite nanoparticles with 10 nm diameter. It is shown that an addition of nanoparticles leads to a widening of separation region, where the Casimir interaction is repulsive. This result does not depend on whether the plasma or the Drude model is used for extrapolation of the optical data of Au to low frequencies. The effect of enhanced repulsion due to the presence of ferrofluid may be useful for preventing stiction of closely spaced elements in various microdevices.

We critically review the possibilities of a repulsive Casimir interaction between materials which carry Chern-Simons surface actions for the electromagnetic field.

We obtain new expressions for the Casimir energy between plates that are mimicked by the most general possible boundary conditions allowed by the principles of quantum field theory. This result enables to provide the quantum vacuum energy for scalar fields propagating under the influence of a one-dimensional crystal represented by a periodic potential formed by an infinite array of identical potentials with compact support.

We consider polarizable sheets modeled by a lattice of delta function potentials. The Casimir interaction of two such lattices is calculated at nonzero temperature. The heat kernel expansion for periodic singular background is discussed in relation with the high temperature asymptote of the free energy.

The Casimir free energy and pressure of thin peptide films deposited on a dielectric substrate are investigated in the region of parameters where they change their sign. Numerical computations are performed for a modelled peptide film on a silica glass plate. The Casimir free energy is computed at room temperature as a function of the film thickness and the fraction of water contained in the film. It is shown that the values of the Casimir pressure change from negative to positive when the film thickness decreases to below some value in the region from 115 to 133 nm depending on the fraction of water in the film. Possible applications of the obtained results to the problem of stability of peptide coatings are discussed.

We demonstrate how the nonrelativistic high energy asymptotics for the photoionization cross sections of systems bound by a central field can be obtained without solving the wave equations. The earlier analysis carried out for s bound states is extended for p states. We show that the physically expected asymptotics for ionization of fullerenes is not reproduced by the model potentials employed nowadays.

We compute the resonance energy transfer (RET) in a system composed of two quantum emitters near a host dielectric matrix in which metallic inclusions are inserted until the medium undergoes a dielectric-metal transition at percolation. We show that there is no peak in the RET rate at percolation, in contrast to what happens with the spontaneous emission rate of an emitter near the same critical medium. This result suggests that RET does not strongly correlate with the local density of states.

A resonant process of annihilation and production of high-energy electron-positron pairs in an external electromagnetic field is studied theoretically. This process is the annihilation channel of an electron-positron scattering. It is shown that the resonance in an external electromagnetic field is possible only when the certain combination of electron and positron initial energies is more than threshold energy. Also, the angle between initial electron and initial positron momenta directions must be small and satisfy the resonant conditions. This angle is determined by the high-energy of the initial pair and the threshold energy. An emerging electron-positron pair also flies out in a narrow cone along the direction of the initial pair and must be ultrarelativistic. For each fixed angle, energies of the final electron and positron can take from one to two values. It is shown that the resonant differential cross section can significantly exceed the corresponding Bhabha cross section without an external field.

The contemporary theoretical investigation researches the resonant emission of high-energy gamma-quanta within the process of scattering of ultrarelativistic electrons on a nucleus in the external electromagnetic field. With implementation of the resonant conditions under the field ambience the particle in the intermediate state re-modulates into the real form. Therefore, the phenomenon examination determines the functional splitting of the second order process into a pair of first-order effects that possess a possibility to develop within two reaction channels. Consequently, the first channel characterizes the kinematics of electron scattering by a nucleus and following radiation of a spontaneous gamma-quantum. The second channel delineates the spontaneous gamma-quantum radiation by an electron with subsequent scattering on a nucleus. It is important to emphasize that within a specific range of observation the calculations derive three discrete magnitudes for the resonant frequency dependency on the angle of spontaneous photon radiation. As a result, the work represents an estimation of the resonant differential scattering cross-section in ratio to the scattering cross-section computed without the external field. In conclusion, various scientific facilities may verify the project data simulation (SLAC, FAIR, XFEL, ELI, XCELS).

The resonant production of electron-positron pairs by a hard gamma-ray on nucleus in an external electromagnetic field is studied theoretically. The main property of this process is that the initial process of the second order in the fine structure constant in an external field effectively splits into two successive processes of the first order due to the fact that in resonant conditions intermediate virtual electron (positron) becomes a real particle. One of these processes is a single-photoproduction of electron-positron pair in a laser field (laser-stimulated Breit-Wheeler process) another is a laser-assisted scattering of electron (positron) on nucleus (laser-assisted Mott scattering). It is shown that the resonances are possible only for the energies of the initial hard gamma-ray more than the characteristic threshold energy. Resonant differential cross section of this process is obtained. It is shown that the resonant differential cross section can significantly exceed the corresponding cross section without an external field. The obtained results may be experimentally verified using the facilities of pulsed laser radiation (SLAC, FAIR, XFEL, ELI, XCELS).

We theoretically investigate the properties of a single-emitter laser with coherent pump: two-level atom interacting with a single damping cavity mode which is resonantly excited by a coherent field. With the help of numerical simulation of the master equation we show that such pumping mechanism is more preferably than incoherent pump for achieving of sub-Poissonian photon statistics.

The contemporary research scrutinizes the resonant Breit-Wheeler process in the field of a plane monochromatic electromagnetic wave. Implementing the weak external field condition the processes of electron-positron pair production advances pre-eminently with participation of restrictively two field photons. Thus, within the resonant state the represented process effectively splits into two first-order processes with respect to the fine-structure constant. In details, the effect indicates the single photon pair production with consequent absorption of gamma quantum by an electron (positron) in the field of the wave. We analyze the resonance kinematics precisely. The study determines specific regions in which the interference of resonant amplitudes is absent. Additionally, the computation obtains a resonant differential cross section for the described areas. The corresponding resonant differential cross section significantly exceeds the correlating Breit-Wheeler cross-section without an external field. Various scientific facilities of pulsed laser radiation may experimentally verify the results of these calculations (SLAC, FAIR, XFEL, ELI, XCELS).

We consider a quantum kinetic equation for $e^{-}{e}^{+}$ plasma created from vacuum under the action of a strong time-dependent linearly polarized electric field. Simplification of the collision integral for photon emission along the polarization direction of the field is discussed.