Method of extending hyperfine coherence times in Pr^3+:Y_2SiO_5

In this letter we present a method for increasing the coherence time of praseodymium hyperfine ground state transitions in Pr^3+:Y_2SiO_5 by the application of a specific external magnetic field. The magnitude and angle of the external field is applied such that the Zeeman splitting of a hyperfine transition is at a critical point in three dimensions, making the first order Zeeman shift vanishingly small for the transition. This reduces the influence of the magnetic interactions between the praseodymium ions and the spins in the host lattice on the transition frequency. Using this method a phase memory time of 82ms was observed, a value two orders of magnitude greater than previously reported. It is shown that the residual dephasing is amenable quantum error correction

Towards climate-smart dairy development

Bill & Melinda Gates Foundatio

Using the CLEANED approach to assess the environmental impacts of livestock production

Bill & Melinda Gates Foundatio

A framework for environmental ex-ante impact assessment of livestock value chains

Livestock and fish industries are a significant source of livelihoods and income globally. They are organised in complex market chains that employ at least 1.3 billion people globally and directly support the livelihoods of 600 million poor smallholder farmers in the developing world. Livestock and fish production, processing and marketing as well as the waste produced along the value chain also cause important environmental impacts. They include atmospheric and water pollution, global warming, soil degradation, water use and pollution and biodiversity loss. Efforts to maximize yields of milk and meat, and to „intensify‟ livestock and fish production, need to be balanced with long-term sustainability and overall efficiency. We must figure out how to produce, process and market livestock and fish in ways that work for individuals, communities and the planet alike. It is thus important to assess environmental impacts before embarking on large-scale development projects geared towards livestock production and aquaculture intensification and value chain transformation. Here we present a generic conceptual framework for environmental ex-ante impact assessment of livestock and fish value chains. It is taking into account all value chain components, different spatial and temporal scales and environmental impacts across different dimensions. The framework guides users through a step-wise procedure for assessing how interventions are likely to change the production system and value chain. Through providing rapid results and flagging the main environmental issues, it can support evidence-based discussions of alternative development pathways

Using the CLEANED approach to assess environmental impacts in the dairy value chain in Tanga, Tanzania

Bill & Melinda Gates Foundatio

A solid state light-matter interface at the single photon level

Coherent and reversible mapping of quantum information between light and matter is an important experimental challenge in quantum information science. In particular, it is a decisive milestone for the implementation of quantum networks and quantum repeaters. So far, quantum interfaces between light and atoms have been demonstrated with atomic gases, and with single trapped atoms in cavities. Here we demonstrate the coherent and reversible mapping of a light field with less than one photon per pulse onto an ensemble of 10 millions atoms naturally trapped in a solid. This is achieved by coherently absorbing the light field in a suitably prepared solid state atomic medium. The state of the light is mapped onto collective atomic excitations on an optical transition and stored for a pre-programmed time up of to 1 mu s before being released in a well defined spatio-temporal mode as a result of a collective interference. The coherence of the process is verified by performing an interference experiment with two stored weak pulses with a variable phase relation. Visibilities of more than 95% are obtained, which demonstrates the high coherence of the mapping process at the single photon level. In addition, we show experimentally that our interface allows one to store and retrieve light fields in multiple temporal modes. Our results represent the first observation of collective enhancement at the single photon level in a solid and open the way to multimode solid state quantum memories as a promising alternative to atomic gases.Comment: 5 pages, 5 figures, version submitted on June 27 200