An NMR Analog of the Quantum Disentanglement Eraser

We report the implementation of a three-spin quantum disentanglement eraser on a liquid-state NMR quantum information processor. A key feature of this experiment was its use of pulsed magnetic field gradients to mimic projective measurements. This ability is an important step towards the development of an experimentally controllable system which can simulate any quantum dynamics, both coherent and decoherent.Comment: Four pages, one figure (RevTeX 2.1), to appear in Physics Review Letter

Transmission of Schistosoma mansoni in Tikur Wuha area, Southern Ethiopia

Background: Although the epidemiology of schistosomiasis is well established and the disease distribution has also been mapped in Ethiopia, discovery of new foci has continuously been reported.Objectives: The objective of this study was to assess the establishment of transmission of schistosomiasis mansoni in Tikur Wuha area, southern Ethiopia.Methods: A cross-sectional epidemiological study involving 375 school children in Tikur Wuha Elementary School was conducted in December 2007 and January 2008. Stool specimens were collected and microscopically examined using Kato-Katz method. Snail survey was also conducted using scoop in Tikur Wuha River and littoral zone of Lake Awassa on the side of Tikur Wuha Kebele (administrative unit). The snails collected were checked for trematode infection by shedding. Laboratory-bred mice were exposed to schistosome cercariae and definite identification of the schistosome was made using eggs and adult worm morphology.Results: The prevalence and intensity of schistosomiasis mansoni was 12% and 69 eggs per gram (epg) of stool, respectively. Biomphalaria sudanica collected in Tikur Wuha River shed schistosome cercariae. Adult S. mansoni worms were harvested from laboratory-bred mice after 6 weeks of laboratory maintenance.Conclusion: The prevalence and intensity of schistosomiasis mansoni among school children was low and the area represents low-risk community. The finding of S. mansoni infected young children, the collection of B. sudanica infected with schistosome cercariae, and the establishment of infection in lab-bred mice all confirmed the transmissionof schistosomiasis mansoni in Tikur Wuha area. Appropriate intervention measures need to be in place to reduce morbidity and transmission of intestinal schistosomiasis in the area

Design of Strongly Modulating Pulses to Implement Precise Effective Hamiltonians for Quantum Information Processing

We describe a method for improving coherent control through the use of detailed knowledge of the system's Hamiltonian. Precise unitary transformations were obtained by strongly modulating the system's dynamics to average out unwanted evolution. With the aid of numerical search methods, pulsed irradiation schemes are obtained that perform accurate, arbitrary, selective gates on multi-qubit systems. Compared to low power selective pulses, which cannot average out all unwanted evolution, these pulses are substantially shorter in time, thereby reducing the effects of relaxation. Liquid-state NMR techniques on homonuclear spin systems are used to demonstrate the accuracy of these gates both in simulation and experiment. Simulations of the coherent evolution of a 3-qubit system show that the control sequences faithfully implement the unitary operations, typically yielding gate fidelities on the order of 0.999 and, for some sequences, up to 0.9997. The experimentally determined density matrices resulting from the application of different control sequences on a 3-spin system have overlaps of up to 0.99 with the expected states, confirming the quality of the experimental implementation.Comment: RevTeX3, 11 pages including 2 tables and 5 figures; Journal of Chemical Physics, in pres

Asmara: Africa’s Modernist City (UNESCO World Heritage Nomination)

In January 2016, the State of Eritrea submitted its first ever application to UNESCO for inscription on the World Heritage List (WHL). The nominated site was the country’s modernist capital, Asmara. The 1,300-page Nomination Dossier represents the distillation of nearly two decades of collaborative research by professionals from a wide range of disciplines in Eritrea and overseas, supported by many national and international government agencies and non-governmental organisations. This paper seeks to summarise the enormous quantity of work contained in the Nomination Dossier and its most important propositions and findings. Asmara is an outstanding example of a colonial capital that bears witness to the universal encounter with modernity in the twentieth century and consequent postcolonial experiences. The historic urban landscape embodies in a whole city the unity of innovative urban planning and modernist architecture combined with local natural and cultural conditions. An urban planning process based on functional and racial zoning demonstrates the Italian colonial response from the late-nineteenth century to the challenges of modern urban requirements in a highland African setting. The architectural character exemplifies a period of intense development in the 1930s that coincided with the global proliferation and artistic apogee of pre-war modernism and its various forms. The research challenges conventional perceptions based on universalistic norms, inviting a reassessment of how colonial heritage and modernism are perceived beyond the Eurocentric gaze. Eritrea’s decision to conserve Asmara’s early colonial era architecture represents a profoundly different attitude towards architectural heritage and its interpretation and treatment compared with many other post-colonial settings. Asmara’s nomination also presents an opportunity to encourage critical reflections on cultural relations and heritage globally, and to promote stability and prosperity locally. The three main aims of the research are: to implement the necessary measures for managing the conservation of Asmara’s heritage assets; to ensure the city’s successful inscription on the WHL; and to contribute to redressing the comparative under-representation of African and modernist sites on the WHL

Spintronics and Quantum Dots for Quantum Computing and Quantum Communication

Control over electron-spin states, such as coherent manipulation, filtering and measurement promises access to new technologies in conventional as well as in quantum computation and quantum communication. We review our proposal of using electron spins in quantum confined structures as qubits and discuss the requirements for implementing a quantum computer. We describe several realizations of one- and two-qubit gates and of the read-in and read-out tasks. We discuss recently proposed schemes for using a single quantum dot as spin-filter and spin-memory device. Considering electronic EPR pairs needed for quantum communication we show that their spin entanglement can be detected in mesoscopic transport measurements using metallic as well as superconducting leads attached to the dots.Comment: Prepared for Fortschritte der Physik special issue, Experimental Proposals for Quantum Computation. 15 pages, 5 figures; typos corrected, references adde

Generation and Suppression of Decoherence in Artificial Environment for Qubit System

It is known that a quantum system with finite degrees of freedom can simulate a composite of a system and an environment if the state of the hypothetical environment is randomized by external manipulation. We show theoretically that any phase decoherence phenomena of a single qubit can be simulated with a two-qubit system and demonstrate experimentally two examples: one is phase decoherence of a single qubit in a transmission line, and the other is that in a quantum memory. We perform NMR experiments employing a two-spin molecule and clearly measure decoherence for both cases. We also prove experimentally that the bang-bang control efficiently suppresses decoherence.Comment: 25 pages, 7 figures; added reference

A Method for Modeling Decoherence on a Quantum Information Processor

We develop and implement a method for modeling decoherence processes on an N-dimensional quantum system that requires only an $N^2$-dimensional quantum environment and random classical fields. This model offers the advantage that it may be implemented on small quantum information processors in order to explore the intermediate regime between semiclassical and fully quantum models. We consider in particular $\sigma_z\sigma_z$ system-environment couplings which induce coherence (phase) damping, though the model is directly extendable to other coupling Hamiltonians. Effective, irreversible phase-damping of the system is obtained by applying an additional stochastic Hamiltonian on the environment alone, periodically redressing it and thereby irreversibliy randomizing the system phase information that has leaked into the environment as a result of the coupling. This model is exactly solvable in the case of phase-damping, and we use this solution to describe the model's behavior in some limiting cases. In the limit of small stochastic phase kicks the system's coherence decays exponentially at a rate which increases linearly with the kick frequency. In the case of strong kicks we observe an effective decoupling of the system from the environment. We present a detailed implementation of the method on an nuclear magnetic resonance quantum information processor.Comment: 12 pages, 9 figure

Experimental Implementation of Hogg's Algorithm on a Three-Quantum-bit NMR Quantum Computer

Using nuclear magnetic resonance (NMR) techniques with three-qubit sample, we have experimentally implemented the highly structured algorithm for the 1-SAT problem proposed by Hogg. A simplified temporal averaging procedure was employed to the three-qubit spin pseudo-pure state. The algorithm was completed with only a single evaluation of structure of the problem and the solutions were found with probability 100%, which outperform both unstructured quantum and the best classical search algorithm.Comment: Revtex, 14 pages and 1 table, 4 EPS figure