We measure the Casimir force between a gold sphere and a silicon plate with nanoscale, rectangular corrugations with a depth comparable to the separation between the surfaces. In the proximity force approximation (PFA), both the top and bottom surfaces of the corrugations contribute to the force, leading to a distance dependence that is distinct from a flat surface. The measured Casimir force is found to deviate from the PFA by up to 10%, in good agreement with calculations based on scattering theory that includes both geometry effects and the optical properties of the material.
A nanopore is an analytical tool with single molecule sensitivity. For detection, a nanopore relies on the electrical signal that develops when a molecule translocates through it. However, the detection sensitivity can be adversely affected by noise and the frequency response. Here, we report measurements of the frequency and noise performance of nanopores =8 nm in diameter in membranes compatible with semiconductor processing. We find that both the high frequency and noise performance are compromised by parasitic capacitances. From the frequency response we extract the parameters of lumped element models motivated by the physical structure that elucidates the parasitics, and then we explore four strategies for improving the electrical performance. We reduce the parasitic membrane capacitances using: (1) thick Si(3)N(4) membranes; (2) miniaturized composite membranes consisting of Si(3)N(4) and polyimide; (3) miniaturized membranes formed from metal-oxide-semiconductor (MOS) capacitors; and (4) capacitance compensation through external circuitry, which has been used successfully for patch clamping. While capacitance compensation provides a vast improvement in the high frequency performance, mitigation of the parasitic capacitance through miniaturization offers the most promising route to high fidelity electrical discrimination of single molecules.
We report measurements of the Casimir force between a gold sphere and a silicon surface with an array of nanoscale, rectangular corrugations using a micromechanical torsional oscillator. At distances between 150 and 500 nm, the measured force shows significant deviations from the pairwise additive formulism, demonstrating the strong dependence of the Casimir force on the shape of the interacting bodies. The observed deviation, however, is smaller than the calculated values for perfectly conducting surfaces, possibly due to the interplay between finite conductivity and geometry effects. DOI: 10.1103/PhysRevLett.101.030401 PACS numbers: 03.70.+k, 12.20.Fv, 12.20.Ds, 42.50.Lc The Casimir force is the interaction between neutral conductors that can be understood as resulting from the alteration of the zero point energy of the electromagnetic field in the presence of boundaries [1]. For two perfect metallic planar surfaces, the force is attractive and is given by F c 2 @cA=240z4 , where c is the speed of light, @ is the Planck's constant=2, z is the separation between the plates, and A is the area of the plates. There exists a close connection between the Casimir force between conductors and the van der Waals (vdW) force between molecules. For the former, the quantum fluctuations are often associated with the vacuum electromagnetic field, while the latter commonly refers to the interaction between fluctuating dipoles. In simple geometries such as two parallel planes, the Casimir force can be interpreted as an extension of the vdW force in the retarded limit. The interaction between molecules in the two plates is summed to yield the total force. However, such summation of the vdW force is not always valid for extended bodies because the vdW force is not pairwise additive. The interaction between two molecules is affected by the presence of a third molecule. One important characteristic of the Casimir force is its strong dependence on geometry [2]. The Casimir energy for a conducting spherical shell [3] or a rectangular box [4,5] has been calculated to have opposite sign to parallel plates. Whether such geometries exhibit repulsive Casimir forces remains a topic of current interest [6].In recent years, there have been a number of precision measurements of the Casimir force [7][8][9][10][11][12][13][14][15]. These experiments yield agreement with the theoretical calculations to accuracies of better than 1% when nonideal behavior of the metallic surfaces [16][17][18] are taken into account. The vast majority of force measurements were performed between a sphere and a flat plate, two flat plates, or two cylinders. For these simple geometries, the Casimir force is not expected to show significant deviations from the pairwise additive approximation (PAA) at small separations. There has only been one experiment that involved surfaces of other geometries, where the Casimir force is measured between a sphere and a plate with small sinusoidal corrugations [19]. While this measurement shows deviations from PAA, the interpret...
We demonstrate free-space space-division-multiplexing (SDM) with 15 orbital angular momentum (OAM) states using a three-dimensional (3D) photonic integrated circuit (PIC). The hybrid device consists of a silica planar lightwave circuit (PLC) coupled to a 3D waveguide circuit to multiplex/demultiplex OAM states. The low excess loss hybrid device is used in individual and two simultaneous OAM states multiplexing and demultiplexing link experiments with a 20 Gb/s, 1.67 b/s/Hz quadrature phase shift keyed (QPSK) signal, which shows error-free performance for 379,960 tested bits for all OAM states.
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