Noninvasiveness and time symmetry of weak measurements

Measurements in classical and quantum physics are described in fundamentally different ways. Nevertheless, one can formally define similar measurement procedures with respect to the disturbance they cause. Obviously, strong measurements, both classical and quantum, are invasive -- they disturb the measured system. We show that it is possible to define general weak measurements, which are noninvasive: the disturbance becomes negligible as the measurement strength goes to zero. Classical intuition suggests that noninvasive measurements should be time symmetric (if the system dynamics is reversible) and we confirm that correlations are time-reversal symmetric in the classical case. However, quantum weak measurements -- defined analogously to their classical counterparts -- can be noninvasive but not time symmetric. We present a simple example of measurements on a two-level system which violates time symmetry and propose an experiment with quantum dots to measure the time-symmetry violation in a third-order current correlation function.Comment: 19 pages, 5 figures, more information at http://www.fuw.edu.pl/~abednorz/tasym

Alkoxylated β-Naphthol as an Additive for Tin Plating from Chloride and Methane Sulfonic Acid Electrolytes

Beta-naphthol was one of the first additives introduced for smooth and homogeneoustin electrodeposition. Although it can be oxidized under the plating conditions, forming either1,2-napthoquinone or polymeric materials based on naphthioxides, it is still in use. In this work,an investigation of its more stable form, alkoxylated beta-naphthol (ABN), on tin plating is undertaken.For this purpose, chloride based (pH ~5) and methane sulfonic acid (MSA, pH ~0.5) electrolytes,including ABN, were prepared. Reaction kinetics were studied by polarization, Tafel measurements,and cyclic voltammetry. Tin electrodeposits were obtained on flat brass substrates. Surfacemorphology and preferred crystal orientation were studied by Scanning Electron Microscopy (SEM)and X-ray Diffraction (XRD). In both studied electrolytes ABN acts as an inhibitor but in the case ofthe chloride electrolyte it is more pronounced. In the MSA electrolyte this effect was overlaid by thepresence of tin-citrate complexes. In the chloride-based electrolyte, ABN has a grain refining effect,while in the MSA electrolyte an increase of ABN concentration leads to a slight enlargement of theaverage grain size. X-ray analysis shows a constant decrease of the (101) intensity with increasingconcentration of ABN for the sample deposited from both baths

Trumpeting M Dwarfs with CONCH-SHELL: a Catalog of Nearby Cool Host-Stars for Habitable ExopLanets and Life

We present an all-sky catalog of 2970 nearby ($d \lesssim 50$ pc), bright ($J< 9$) M- or late K-type dwarf stars, 86% of which have been confirmed by spectroscopy. This catalog will be useful for searches for Earth-size and possibly Earth-like planets by future space-based transit missions and ground-based infrared Doppler radial velocity surveys. Stars were selected from the SUPERBLINK proper motion catalog according to absolute magnitudes, spectra, or a combination of reduced proper motions and photometric colors. From our spectra we determined gravity-sensitive indices, and identified and removed 0.2% of these as interloping hotter or evolved stars. Thirteen percent of the stars exhibit H-alpha emission, an indication of stellar magnetic activity and possible youth. The mean metallicity is [Fe/H] = -0.07 with a standard deviation of 0.22 dex, similar to nearby solar-type stars. We determined stellar effective temperatures by least-squares fitting of spectra to model predictions calibrated by fits to stars with established bolometric temperatures, and estimated radii, luminosities, and masses using empirical relations. Six percent of stars with images from integral field spectra are resolved doubles. We inferred the planet population around M dwarfs using $Kepler$ data and applied this to our catalog to predict detections by future exoplanet surveys.Comment: Accepted to MNRAS 22 figures, 3 tables, 2 electronic tables. Electronic tables are available as links on this pag