Evolution of entanglement between distinguishable light states

We investigate the evolution of quantum correlations over the lifetime of a multiphoton state. Measurements reveal time-dependent oscillations of the entanglement fidelity for photon pairs created by a single semiconductor quantum dot. The oscillations are attributed to the phase acquired in the intermediate, nondegenerate, exciton-photon state and are consistent with simulations. We conclude that emission of photon pairs by a typical quantum dot with finite polarization splitting is in fact entangled in a time-evolving state, and not classically correlated as previously regarded.     

Mid-infrared luminescence from coupled quantum dots and wells

Coupled nanostructures have been developed in the InAs/InSb/GaSb materials system in order to extend the emission wavelength further into the infrared, beyond 2 μm. The samples studied consist of a single narrow InAs quantum well grown below a layer of InSb quantum dots in a GaSb matrix, in which the coupling has been altered by changing the thickness of a GaSb spacer layer. The overall transition energy of the combined dot–well system is generally reduced with respect to the dots and well only but the dependence on spacer thickness is more complex than that expected from a simple envelope function model.     

Weak and very weak Bernoulli partitions

The definitions of weak and very weak Bernoulli are reformulated to allow conditioning with respect to the entire past. For skew products which are measurable with respect to an independent generator of the base this reformulation allows one to state simple necessary and sufficient conditions for weak and very weak Bernoulli. We use these ideas to give a simple example of a partition which is very weak but not weak Bernoulli.This research was done while the author visited Stanford, supported in part by N. S. F. Grant MP 575-08324.     

Crystal morphology, composition, and dissolution behavior of carbonated apatites prepared at controlled pH and temperature

A range of carbonated apatites was prepared by aqueous precipitation at 37, 60, and 85°C and at controlled pH values varying from 6.00–9.50 in 0.25 increments. The products were analyzed for Ca, P, Sr, Mg, Na, F, and carbonate. Their initial dissolution rates were measured in a pH 4.5, 0.01 mol · liter⁻¹ acetate buffer. Information about crystal morphologies and crystal defects was obtained by x-ray diffraction and high-resolution transmission electron microscopy (TEM). The molar ratios of the products, together with their Sr and Mg contents, increased with increasing pH. Initial dissolution rates of the products, when adjusted for carbonate content, were in the order 37 > 60 > 85°C whereas apparent particle sizes determined by TEM and x-ray diffraction were ordered 37 < 60 < 85°C. Carbonated apatites precipitated at pHs of 7.0 or less were observed to have planar defects parallel to (100) that were identified as unit-cell-thick intergrowths of octacalcium phosphate. Carbonated apatites precipitated at higher pHs and noncarbonated apatites did not have these defects. A crystal growth mechanism is proposed to account for the presence of the (100) defects.     

Une remarque sur les isomorphismes de schemas de Bernoulli qui preservent certains facteurs

By slightly strengthening the hypothesis, we quickly arrive at, in a new case, some results from the paperRemarques sur les systèmes dynamiques donnés avec plusieurs facteurs.     

Phase transitions in tungsten trioxide at low temperatures

Capacitance and electrical resistivity measurements have been made on stoichiometric and on oxygen-deficient tungsten trioxide crystals from 4.2 to 300°K. X ray oscillation and rotation photographs were made on single crystals of both materials near 200°K and near 300°K. Capacitance and resistivity anomalies identify phase transitions near 40, 65, 130, 220, and 260°K in stoichiometric WO₃. Resistivity anomalies occur near 80, 130, 220, and 260°K in oxygen-deficient tungsten trioxide. Capacitance measurements suggest that the transformation at 130°K of a low-temperature phase to a high-temperature phase of stoichiometric WO₃ is associated with a doubling of thec-parameter of the unit cell. Resistivity measurements establish probable conduction mechanisms in each phase of stoichiometric and of oxygen-deficient tungsten trioxide, and show that oxygen-deficient tungsten trioxide undergoes a semiconductor-to-metal transition near 220°K. Electronic phenomena that do not appear to be associated with structural phase transformations are observed near 16°K in stoichiometric WO₃.