Optical readout of charge and spin in a self-assembled quantum dot in a strong magnetic field

We present a theory and experiment demonstrating optical readout of charge and spin in a single InAs/GaAs self-assembled quantum dot. By applying a magnetic field we create the filling factor 2 quantum Hall singlet phase of the charged exciton. Increasing or decreasing the magnetic field leads to electronic spin-flip transitions and increasing spin polarization. The increasing total spin of electrons appears as a manifold of closely spaced emission lines, while spin flips appear as discontinuities of emission lines. The number of multiplets and discontinuities measures the number of carriers and their spin. We present a complete analysis of the emission spectrum of a single quantum dot with N=4 electrons and a single hole, calculated and measured in magnetic fields up to 23 Tesla.Comment: 9 pages, 3 figures, submitted to Europhysics Letter

Experimental implementation of encoded logical qubit operations in a perfect quantum error correcting code

Large-scale universal quantum computing requires the implementation of quantum error correction (QEC). While the implementation of QEC has already been demonstrated for quantum memories, reliable quantum computing requires also the application of nontrivial logical gate operations to the encoded qubits. Here, we present examples of such operations by implementing, in addition to the identity operation, the NOT and the Hadamard gate to a logical qubit encoded in a five qubit system that allows correction of arbitrary single qubit errors. We perform quantum process tomography of the encoded gate operations, demonstrate the successful correction of all possible single qubit errors and measure the fidelity of the encoded logical gate operations

Archaeological Testing of Four Sites on Camp Bowie, Brown County, Texas

In August of 2002, a crew from the Center for Archaeological Research (CAR) of The University of Texas at San Antonio tested four sites at Camp Bowie in Brown County Texas. Three sites, 41BR471, 41BR500, and 41BR522, were prehistoric and one site, 41BR392, had both historic and prehistoric components. This work was done under Texas Antiquities Permit No. 2926 for the Adjutant General’s Department of Texas. Testing at these sites was done based on recommendations made for 41BR500 by Mauldin and Broehm (2001) and recommendations made for 41BR392, 41BR471 and 41BR522 by Greaves (2002). Testing at 41BR392 centered on a prehistoric burned rock midden. Excavations took place in and around the midden. A few bifaces and a considerable amount of lithic debris were recovered. The size, location and density of burned rock within the midden were examined as a means of investigating the internal midden structure. Analysis of these data suggest that the midden represents an earth oven. Ethnobotanical recovery revealed the presence of geophytes. Radiocarbon dates place the feature within the Late Prehistoric period. Testing at 41BR471 involved surface collection and excavation. Excavations confirmed that the site is deflated with sub-surface deposits being shallow and very minor. What remains of this site is a moderate to dense surface scatter of unmodified debitage and a few lithic cores. Testing at 41BR500 centered on a suspected buried burned rock feature discovered during the spring 2001 survey. Excavations recovered unmodified lithic debitage, biface fragments and a scraper. Excavations in a separate area of the site where high debitage density was noted recovered a Nolan dart point dating to the Middle Archaic along with a number of bifaces and a considerable amount of unmodified lithic debitage. This additional testing uncovered a single charcoal stain, and radiocarbon dates place this feature within the Late Prehistoric period. Our analysis of the distribution of the diagnostic points, the distribution of debitage, and the radiocarbon date, suggest that much of this material is in secondary context. Test excavations at 41BR522 showed very little debitage in or around the prehistoric burned rock midden. This small midden is nearly a perfect ring of burned rock surrounding a central hearth depression. Preservation was excellent for the recovery of both charred botanical remains and for examination of the midden structure. A Montell dart point, dating to the Late Archaic was recovered. As with 41BR392, the size, location and density of burned rock within the midden was examined as a means of investigating the internal midden structure. Analysis revealed the midden to be a central hearth/earth-oven type burned rock midden. Ethnobotanical recovery revealed the presence of geophytes. Radiocarbon dates place the feature within the Late Prehistoric period. Based on the results of this testing, it is recommended that sites 41BR471 and 41BR500 are not eligible to the National Register of Historic Places and do not warrant status as State Archeological Landmarks. The sites have data that are of questionable integrity, and CAR’s testing work has effectively exhausted any remaining research potential. Sites 41BR392 and 41BR522 are recommended as eligible to the National Register of Historic Places and do warrant status as State Archeological Landmarks. Both recommended sites have data with good integrity. In addition, both sites have charcoal present, and good recovery of ethnobotanical material. Data from these sites can be used to consider a variety of research questions that are significant for understanding the prehistory of the region

Managing weather and climate risks to agriculture in North America, Central America and the Caribbean

AbstractIn recent decades, numerous weather- and climate-related natural disasters have impacted North America, Central America, and the Caribbean, repeatedly demonstrating how vulnerable local agriculture is to extreme episodic events. Given this recent history, and expectations that the frequency and intensity of some episodic events will increase with climate change, it is becoming increasingly important for farmers to proactively manage weather and climate risks to agriculture to protect their livelihoods. Some farmers in this region already apply various strategies to help reduce weather and climate risks and uncertainties, including farming in multiple locations, diversifying crops and varieties, seeking alternative sources of income, and purchasing crop insurance. Such efforts often help farmers maintain a more stable income while also protecting and preserving the productivity of the land. Other farmers, however, have failed to implement basic risk management strategies despite the clear benefits. Reasons for these failures can be attributed to inadequate farmer education and training, a lack of tools to help facilitate the practical application of risk management concepts, and poor communications between the agrometeorological and farming communities. The agrometeorological community can help overcome these obstacles by building upon existing efforts that have successfully educated farmers about weather and climate risks to agriculture and have equipped farmers with the data, tools, and applications necessary to manage these risks. Farmer input is critical to preparing effective educational and training materials and developing user-friendly risk management tools. The agrometeorological community should solicit input from farmers regularly to ensure that farmers are obtaining the information necessary to effectively manage weather and climate risks to agriculture

Semiparametric Regression During 2003–2007

Semiparametric regression is a fusion between parametric regression and nonparametric regression and the title of a book that we published on the topic in early 2003. We review developments in the field during the five year period since the book was written. We find semiparametric regression to be a vibrant field with substantial involvement and activity, continual enhancement and widespread application

Magnetoelectric domains and their switching mechanism in a Y-type hexaferrite

By employing resonant X-ray microdiffraction, we image the magnetisation and magnetic polarity domains of the Y-type hexaferrite Ba$_{0.5}$Sr$_{1.5}$Mg$_2$Fe$_{12}$O$_{22}$. We show that the magnetic polarity domain structure can be controlled by both magnetic and electric fields, and that full inversion of these domains can be achieved simply by reversal of an applied magnetic field in the absence of an electric field bias. Furthermore, we demonstrate that the diffraction intensity measured in different X-ray polarisation channels cannot be reproduced by the accepted model for the polar magnetic structure, known as the 2-fan transverse conical (TC) model. We propose a modification to this model, which achieves good quantitative agreement with all of our data. We show that the deviations from the TC model are large, and may be the result of an internal magnetic chirality, most likely inherited from the parent helical (non-polar) phase.Comment: 9 figure