True photo-counting statistics of multiple on-off detectors

We derive a closed photo-counting formula, including noise counts and a finite quantum efficiency, for photon number resolving detectors based on on-off detectors. It applies to detection schemes such as array detectors and multiplexing setups. The result renders it possible to compare the corresponding measured counting statistics with the true photon number statistics of arbitrary quantum states. The photo-counting formula is applied to the discrimination of photon numbers of Fock states, squeezed states, and odd coherent states. It is illustrated for coherent states that our formula is indispensable for the correct interpretation of quantum effects observed with such devices.Comment: 7 pages, 4 figure

How ripples turn into dots: modeling ion-beam erosion under oblique incidence

Pattern formation on semiconductor surfaces induced by low energetic ion-beam erosion under normal and oblique incidence is theoretically investigated using a continuum model in form of a stochastic, nonlocal, anisotropic Kuramoto-Sivashinsky equation. Depending on the size of the parameters this model exhibits hexagonally ordered dot, ripple, less regular and even rather smooth patterns. We investigate the transitional behavior between such states and suggest how transitions can be experimentally detected.Comment: 11 pages, 4 figures, submitted for publication, revised versio

Use of tunable nanopore blockade rates to investigate colloidal dispersions

Tunable nanopores in elastomeric membranes have been used to study the dependence of ionic current blockade rate on the concentration and electrophoretic mobility of particles in aqueous suspensions. A range of nanoparticle sizes, materials and surface functionalities has been tested. Using pressure-driven flow through a pore, the blockade rate for 100 nm carboxylated polystyrene particles was found to be linearly proportional to both transmembrane pressure (controlled between 0 and 1.8 kPa) and particle concentration (between 7 x 10^8 and 4.5 x 10^10 mL^-1). This result can be accurately modelled using Nernst-Planck transport theory. Using only an applied potential across a pore, the blockade rates for carboxylic acid and amine coated 500 nm and 200 nm silica particles were found to correspond to changes in their mobility as a function of the solution pH. Scanning electron microscopy and confocal microscopy have been used to visualise changes in the tunable nanopore geometry in three dimensions as a function of applied mechanical strain. The pores observed were conical in shape, and changes in pore size were consistent with ionic current measurements. A zone of inelastic deformation adjacent to the pore has been identified as critical in the tuning process

Spontaneous decay of excited atomic states near a carbon nanotube

Spontaneous decay process of an excited atom placed inside or outside (near the surface) a carbon nanotube is analyzed. Calculations have been performed for various achiral nanotubes. The effect of the nanotube surface has been demonstrated to dramatically increase the atomic spontaneous decay rate -- by 6 to 7 orders of magnitude compared with that of the same atom in vacuum. Such an increase is associated with the nonradiative decay via surface excitations in the nanotube.Comment: 8 pages, 3 figure

Diverse Supernova Sources for the r-Process

(Abridged) It is shown that a semi-quantitative agreement with the gross solar r-process abundance pattern near and above mass number A=130 can be obtained by a superposition of two distinctive kinds of supernova r-process events. These correspond to a low frequency case L and a high frequency case H, which takes into account the low abundance of I129 and the high abundance of Hf182 in the early solar nebula. The lifetime of Hf182 associates the events in case H with the most common Type II supernovae. These events would be mainly responsible for the r-process nuclei near and above A=195. They would also make a significant amount of the nuclei between A=130 and 195, including Hf182, but very little I129. In order to match the solar r-process abundance pattern and to satisfy the I129 and Hf182 constraints, the events in case L, which would make the r-process nuclei near A=130 and the bulk of those between A=130 and 195, must occur 10 times less frequently but eject 10--20 times more r-process material in each event. We speculate that the usual neutron star remnants, and hence prolonged ejection of r-process material, are associated with the events in case L, whereas the more frequently occurring events in case H have ejection of other r-process material terminated by black hole formation during the neutrino cooling phase of the protoneutron star.Comment: 23 pages, AAS LATEX, 8 Postscript figure

High domain wall velocities induced by current in ultrathin Pt/Co/AlOx wires with perpendicular magnetic anisotropy

Current-induced domain wall (DW) displacements in an array of ultrathin Pt/Co/AlOx wires with perpendicular magnetic anisotropy have been directly observed by wide field Kerr microscopy. DWs in all wires in the array were driven simultaneously and their displacement on the micrometer-scale was controlled by the current pulse amplitude and duration. At the lower current densities where DW displacements were observed (j less than or equal to 1.5 x 10^12 A/m^2), the DW motion obeys a creep law. At higher current density (j = 1.8 x 10^12 A/m^2), zero-field average DW velocities up to 130 +/- 10 m/s were recorded.Comment: Minor changes to Fig. 1(b) and text, correcting for the fact that domain walls were subsequently found to move counter to the electron flow. References update

Sub-binomial light

The click statistics from on-off detector systems is quite different from the counting statistics of the more traditional detectors. This necessitates introduction of new parameters to characterize the nonclassicality of fields from measurements using on-off detectors. To properly replace the Mandel Q_M parameter, we introduce a parameter Q_B. A negative value represents a sub-binomial statistics. This is possible only for quantum fields, even for super-Poisson light. It eliminates the problems encountered in discerning nonclassicality using Mandel's Q_M for on-off data.Comment: 3 figure