We have performed precision electrostatic calibrations in the sphere-plane geometry and observed anomalous behavior. Namely, the scaling exponent of the electrostatic signal with distance was found to be smaller than expected on the basis of the pure Coulombian contribution and the residual potential found to be distance dependent. We argue that these findings affect the accuracy of the electrostatic calibrations and invite reanalysis of previous determinations of the Casimir force

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A two-dimensional computational methodology has been developed that uses a phenomenological representation of initial perturbations to model the evolution of magnetically driven Rayleigh-Taylor instabilities in a hollow Z pinch. The perturbed drive current waveform and x-ray output obtained from the two-dimensional models differ qualitatively from the results of unperturbed ͑one-dimensional͒ models. Furthermore, the perturbed results reproduce the principle features measured in a series of capacitor bank-driven pulsed power experiments. In this paper we discuss the computational approach and the computational sensitivity to initial conditions ͑including the initial perturbations͒. Representative examples are also presented of instability evolution during implosions, and the results are compared with experimentally measured current waveforms and visible framing camera images of perturbed implosions. Standard magnetohydrodynamic modeling, which includes instability growth in two dimensions, is found to reproduce the features seen in experiments.

An economical, coherent, and widely tunable source does not exist spanning the far-infrared electromagnetic spectral range of 50–1000μm in wavelength. The Čerenkov free-electron laser (CFEL) is a promising candidate. This report describes an experimental investigation of a compact CFEL driven by a high-quality low-energy electron beam. Čerenkov emission and strong gain but remarkably low output coupling were observed.

We propose an experiment for generating and detecting vacuum-induced dissipative motion. A high frequency mechanical resonator driven in resonance is expected to dissipate mechanical energy in quantum vacuum via photon emission. The photons are stored in a high quality electromagnetic cavity and detected through their interaction with ultracold alkali-metal atoms prepared in an inverted population of hyperfine states. Superradiant amplification of the generated photons results in a detectable radio-frequency signal temporally distinguishable from the expected background.

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In a recent Comment, Decca et al. have discussed the origin of the anomalies recently reported by us in [Phys. Rev. A 78, 036102(R) (2008)]. Here we restate our view, corroborated by their considerations, that quantitative geometrical and electrostatic characterizations of the conducting surfaces (a topic not discussed explicitly in the literature until very recently) are critical for the assessment of precision and accuracy of the demonstration of the Casimir force, and for deriving meaningful limits on the existence of Yukawian components possibly superimposed to the Newtonian gravitational interaction.In the last decade, various efforts have been focused on demonstrating the Casimir force and exploring hypothetical short-range forces of gravitational origin [1]. Limits to the existence of these forces -or their tentative discovery -in the micrometer range rely on the control at the highest level of accuracy of the Casimir force and the related systematic effects [2,3].In this context we have investigated the celebrated sphere-plane geometry in a range of parameters for which the hypothetical Yukawian contribution of gravitational origin should be optimally detected [4]. This implies exploiting a combination of spheres with large radius of curvature, such as the one already used in [5], and small separation gaps between the sphere and the planar surface, similar to the ones explored in [6,7,8] with spheres having order of 100 µm radius of curvature. Notice that large radius of curvature and relatively large distances as in [5] are not adequately sensitive to Yukawian forces with small interaction range. Conversely, microspheres at small distances as used in [6,7,8] have small sensitivity to the amplitude of Yukawa forces, due to the smaller expected signal arising from the reduced effective surfaces of interaction. In this regard, limits to the Yukawa force based on a formal mapping between an ideal parallel plate geometry and the sphere-plane configuration actually used in the experimental setup as in [9] are invalid, as the Proximity Force Approximation (PFA), typically used for forces acting between surfaces [10], does not hold for forces of volumetric character such as the gravitational force or its hypothetical short-range relatives.In [4], we reported two anomalies in the electrostatic calibration of our apparatus, after discussing and ruling out some systematic effects. This has triggered the interest of the authors of [11] who have added two interesting points, first attempting to explain our first anomaly in terms of a systematic deviation from the ideal, singlecurvature pattern for the spherical surface, and second presenting a distance independent contact potential in one of their experimental setups. We welcome these different insights and would like to discuss here their implications in the general context of both accurate demonstrations of the Casimir force and precision experiments on Yukawian gravitational forces, as in the following.Deviation from ideal spherical geometry: Among the possible re...

We report on current efforts to detect the thermal and dissipative contributions to the Casimir force. For the thermal component, two experiments are in progress at Dartmouth and at the Institute Laue Langevin in Grenoble. The first experiment will seek to detect the Casimir force at the largest explorable distance using a cylinder-plane geometry which offers various advantages with respect to both sphere-plane and parallel plane geometries. In the second experiment, the Casimir force in the parallel plane configuration is measured with a dedicated torsional balance, up to 10 µm. Parallelism of large surfaces, critical for this configuration, is maintained through the use of inclinometer technology already implemented at Grenoble for the study of gravitationally bound states of ultracold neutrons. For the dissipative component of the Casimir force, we discuss detection techniques based upon the use of hyperfine spectroscopy of ultracold atoms and Rydberg atoms. Although quite challenging, this triad of experimental efforts, if successful, will give us a better knowledge of the interplay between quantum and thermal fluctuations of the electromagnetic field and of the nature of dissipation induced by motion of objects in quantum vacuum.