IS THERE A CLASSICAL ANALOG OF A QUANTUM TIME-TRANSLATION MACHINE?

In a recent article [D. Suter, Phys. Rev. {\bf A 51}, 45 (1995)] Suter has claimed to present an optical implementation of the quantum time-translation machine which ``shows all the features that the general concept predicts and also allows, besides the quantum mechanical, a classical description.'' It is argued that the experiment proposed and performed by Suter does not have the features of the quantum time-translation machine and that the latter has no classical analog.Comment: 7 pages, LaTe

Room-temperature high-speed nuclear-spin quantum memory in diamond

Quantum memories provide intermediate storage of quantum information until it is needed for the next step of a quantum algorithm or a quantum communication process. Relevant figures of merit are therefore the fidelity with which the information can be written and retrieved, the storage time, and also the speed of the read-write process. Here, we present experimental data on a quantum memory consisting of a single $^{13}$C nuclear spin that is strongly coupled to the electron spin of a nitrogen-vacancy (NV) center in diamond. The strong hyperfine interaction of the nearest-neighbor carbon results in transfer times of 300 ns between the register qubit and the memory qubit, with an overall fidelity of 88 % for the write - storage - read cycle. The observed storage times of 3.3 ms appear to be limited by the T$_1$ relaxation of the electron spin. We discuss a possible scheme that may extend the storage time beyond this limit.Comment: 7 pages, 6 figure

"Context effects in a negative externality experiment"

This study investigates the degree to which framing and context influence observed rates of free-riding behavior in a negative externality laboratory experiment. Building on the work of Andreoni (1995a) and Messer et al. (2007) we frame the decision not to contribute to a public fund as generating a negative externality on other group members. The experimental treatments involving 252 subjects vary communication, voting, and the status quo of the initial endowment. Results indicate that allowing groups the opportunity to communicate and vote significantly reduces rates of free-riding, and this effect is especially pronounced when initial endowments are placed in the private as opposed to the public fund.Negative externality; voluntary contribution mechanism; cheap talk; voting; status quo bias; experimental economics

Background Initialization with A New Robust Statistical Approach

© 2005 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.Initializing a background model requires robust statistical methods as the task should be robust against random occurrences of foreground objects, as well as against general image noise. The median has been employed for the problem of background initialization. However, the median has only a breakdown point of 50%. In this paper, we propose a new robust method which can tolerate more than 50% of noise and foreground pixels in the background initialization process. We compare our new method with five others and give quantitative evaluations on background initialization. Experiments show that the proposed method achieves very promising results in background initialization.Hanzi Wang and D. Sute

Nuclear spin qubits in a trapped-ion quantum computer

Physical systems must fulfill a number of conditions to qualify as useful quantum bits (qubits) for quantum information processing, including ease of manipulation, long decoherence times, and high fidelity readout operations. Since these conditions are hard to satisfy with a single system, it may be necessary to combine different degrees of freedom. Here we discuss a possible system, based on electronic and nuclear spin degrees of freedom in trapped ions. The nuclear spin yields long decoherence times, while the electronic spin, in a magnetic field gradient, provides efficient manipulation, and the optical transitions of the ions assure a selective and efficient initialization and readout.Comment: 7 page

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

Experimental Realization of 1→21 \to 2 Asymmetric Phase-Covariant Quantum Cloning

While exact cloning of an unknown quantum state is prohibited by the linearity of quantum mechanics, approximate cloning is possible and has been used, e.g., to derive limits on the security of quantum communication protocols. In the case of asymmetric cloning, the information from the input state is distributed asymmetrically between the different output states. Here, we consider asymmetric phase-covariant cloning, where the goal is to optimally transfer the phase information from a single input qubit to different output qubits. We construct an optimal quantum cloning machine for two qubits that does not require ancilla qubits and implement it on an NMR quantum information processor.Comment: 6 pages, 5 figure

Der optimale Erntezeitpunkt für tanninhaltige Futterpflanzen

Depending on the concentration in which they are fed, condensed tannins (CT) can have various beneficial or detrimental effects on ruminants. In organic farming the anthelmintic effects of CT are of special interest. In an outdoor experiment, the sea-sonal dynamics of the CT concentration of the harvestable biomass was investigated as a function of the biomass allocation to leaves and stems in Onobrychis viciifolia, Lotus corniculatus and Cichorium intybus in the course of a vegetation period in Zu-rich, Switzerland. Such knowledge is indispensable for a practical application of tan-niferous plants in farming systems. In line with our expectations, CT concentrations were higher in leaves than in stems and the leaf fraction of the harvestable biomass decreased steeply with time in all investigated plant species. In contrast to our expec-tations, within 20 weeks from sowing, the concentration of CT in leaves approximately doubled in Lotus (from 2 to 5% of DM) and in Onobrychis (from 5 to 9% of DM) and was nearly stable in Cichorium (0.5% of DM). Over time, the effect of the declining proportion of leaves in the harvestable biomass was almost exactly neutralized by the increasing concentration of CT in leaves, resulting in close to constant CT concentra-tions in the harvestable biomass during the season. We conclude that among the investigated species, the tannin concentration in Onobrychis seems most promising for the application against gastro-intestinal nematodes. As the CT concentration of harvestable biomass was found to be constant during the season, an optimal time for harvest can be determined in relation to agronomic properties such as fodder quality and yield

Mechanism of Exfoliation and Prediction of Materials Properties of Clay-Polymer Nanocomposites from Multiscale Modeling

We describe the mechanism that leads to full exfoliation and dispersion of organophilic clays when mixed with molten hydrophilic polymers. This process is of fundamental importance for the production of clay-polymer nanocomposites with enhanced materials properties. The chemically specific nature of our multiscale approach allows us to probe how chemistry, in combination with processing conditions, produces such materials properties at the mesoscale and beyond. In general agreement with experimental observations, we find that a higher grafting density of charged quaternary ammonium surfactant ions promotes exfoliation, by a mechanism whereby the clay sheets slide transversally over one another. We can determine the elastic properties of these nanocomposites; exfoliated and partially exfoliated morphologies lead to substantial enhancement of the Young's modulus, as found experimentally

Machinery use and investment on Missouri farms, 1951

This bulletin is a report on Department of Agricultural Economics Research Project Number 88, entitled 'Cost and Practice Problems of Farm Power and Machinery Modernization'--P. [2].Digitized 2007 AES.Includes bibliographical references